Search

Background: The resurgence of colistin has become critical in combating multidrug-resistant Gram-negative bacteria. However, the emergence of mobilized colistin resistance (mcr) genes presents a crucial global challenge, particularly in the Arab world, which includes regions with unique conditions and ongoing conflicts in some parts. Methods: To address this issue, a systematic review was conducted using multiple databases, including Cochrane, PubMed, Scopus, Web of Science, and Arab World Research Source. Results: A total of 153 studies were included, revealing substantial heterogeneity in the prevalence of mcr genes across 15 Arab countries, with notable findings indicating that Egypt and Lebanon reported the highest number of cases. The analysis indicated that the most prevalent sequence types were ST10, ST101, and ST1011, all of which are Escherichia coli strains linked to significant levels of colistin resistance and multiple antimicrobial resistance profiles. Conclusions: By analyzing the diverse findings from different Arab countries, this review lays a critical foundation for future research and highlights the necessity for enhanced surveillance and targeted interventions to address the looming threat of colistin resistance in the region. Systematic review registration: PROSPERO CRD42024584379. [ABSTRACT FROM AUTHOR]

Abstract Pasteurella aerogenes has been implicated in reproductive disorders in sows, yet its prevalence and characteristics in vaginal discharge are not well understood. This study aimed to detect P. aerogenes in sow vaginal discharge samples and investigate its antibiotic resistance profile, toxin genes, and toxicity. P. aerogenes was isolated from 40% (8/20) of samples. Antimicrobial susceptibility testing revealed universal resistance to amoxicillin-clavulanate (4:1), with 87.5% of isolates also resistant to oxytetracycline, amoxicillin, ceftriaxone, and enrofloxacin. The colistin resistance gene mcr-2 was detected in 75% of isolates, while class 1 integron (int1) was found in 12.5%. The pax toxin gene cluster was present in 75% of isolates. Toxicity assays using Panagrellus redivivus demonstrated dose-dependent effects of P. aerogenes supernatant containing pax toxins. This study represents the first report of P. aerogenes isolation from sow vaginal discharge in Thailand. The high prevalence of antibiotic resistance, presence of the mcr-2 gene, and toxicity of pax toxin-positive isolates suggest that P. aerogenes may be an underestimated factor in swine reproductive health. These findings highlight the need for further investigation into the role of P. aerogenes in sow reproductive disorders and its potential impact on swine production.

Abstract Background Carbapenemase-producing Klebsiella pneumoniae (CRKP) presents a significant challenge to antimicrobial therapy, especially when compounded by resistance to colistin. The objective of this study was to explore molecular epidemiological insights into strains of clinical K. pneumoniae that produce carbapenemases and exhibit resistance to colistin. Eighty clinical isolates of CRKP were obtained from Milad Hospital in Tehran, Iran. Antimicrobial susceptibility and colistin broth disk elution were determined. PCR assays were conducted to examine the prevalence of resistance-associated genes, including bla KPC , bla IMP , bla VIM , bla OXA−48 , bla NDM and mcr-1 to -10. Molecular typing (PFGE) was used to assess their spread. Results Colistin resistance was observed in 27 isolates (33.7%) using the Broth Disk Elution method. Among positive isolates for carbapenemase genes, the most frequent gene was bla OXA−48 , identified in 36 strains (45%). The mcr-1 gene was detected in 3.7% of the obtained isolates, with none of the other of the other mcr genes detected in the studied isolates. Conclusion To stop the spread of resistant K. pneumoniae and prevent the evolution of mcr genes, it is imperative to enhance surveillance, adhere rigorously to infection prevention protocols, and implement antibiotic stewardship practices.

Background: Carbapenemase-producing Klebsiella pneumoniae (CRKP) presents a significant challenge to antimicrobial therapy, especially when compounded by resistance to colistin. The objective of this study was to explore molecular epidemiological insights into strains of clinical K. pneumoniae that produce carbapenemases and exhibit resistance to colistin. Eighty clinical isolates of CRKP were obtained from Milad Hospital in Tehran, Iran. Antimicrobial susceptibility and colistin broth disk elution were determined. PCR assays were conducted to examine the prevalence of resistance-associated genes, including blaKPC, blaIMP, blaVIM, blaOXA−48, blaNDM and mcr-1 to -10. Molecular typing (PFGE) was used to assess their spread. Results: Colistin resistance was observed in 27 isolates (33.7%) using the Broth Disk Elution method. Among positive isolates for carbapenemase genes, the most frequent gene was blaOXA−48, identified in 36 strains (45%). The mcr-1 gene was detected in 3.7% of the obtained isolates, with none of the other of the other mcr genes detected in the studied isolates. Conclusion: To stop the spread of resistant K. pneumoniae and prevent the evolution of mcr genes, it is imperative to enhance surveillance, adhere rigorously to infection prevention protocols, and implement antibiotic stewardship practices. [ABSTRACT FROM AUTHOR]

Antibiotic resistance has emerged as a significant global public health issue, driven by the rapid adaptation of microorganisms to commonly prescribed antibiotics. Colistin, previously regarded as a last-resort antibiotic for treating infections caused by Gram-negative bacteria, is increasingly becoming resistant due to chromosomal mutations and the acquisition of resistance genes carried by plasmids, particularly the mcr genes. The mobile colistin resistance gene (mcr-1) was first discovered in E. coli from China in 2016. Since that time, studies have reported different variants of mcr genes ranging from mcr-1 to mcr-10, mainly in Enterobacteriaceae from various parts of the world, which is a major concern for public health. The co-presence of colistin-resistant genes with other antibiotic resistance determinants further complicates treatment strategies and underscores the urgent need for enhanced surveillance and antimicrobial stewardship efforts. Therefore, understanding the mechanisms driving colistin resistance and monitoring its global prevalence are essential steps in addressing the growing threat of antimicrobial resistance and preserving the efficacy of existing antibiotics. This review underscores the critical role of colistin as a last-choice antibiotic, elucidates the mechanisms of colistin resistance and the dissemination of resistant genes, explores the global prevalence of mcr genes, and evaluates the current detection methods for colistin-resistant bacteria. The objective is to shed light on these key aspects with strategies for combating the growing threat of resistance to antibiotics. [ABSTRACT FROM AUTHOR]

Abstract Background Camels harbouring multidrug-resistant Gram-negative bacteria are capable of transmitting various microorganisms to humans. This study aimed to determine the distribution of anti-microbial resistance among Escherichia coli (E. coli) isolated from the feces of apparently healthy camels in Egyptian abattoirs. Additionally, we sought to characterize Shiga toxin-producing E. coli (STEC) strains, assess their virulence potential, and investigate the possibility of camels spreading carbapenem- and colistin-resistant E. coli. Methods 121 fecal swaps were collected from camels in different abattoirs in Egypt. Isolation and identification of E. coli were performed using conventional culture techniques and biochemical identification. All isolates obtained from the examined samples underwent genotyping through polymerase chain reaction (PCR) of the Shiga toxin-encoding genes (Stx1 and Stx2), the carbapenemase-encoding genes (bla KPC , bla OXA−48 , bla NDM , and bla VIM ), and the mcr genes for mcr-1 to mcr-5. Result Bacteriological examination revealed 75 E. coli isolates. PCR results revealed that one strain (1.3%) tested positive for Stx1, and five (6.6%) were positive for Stx2. Among the total 75 strains of E. coli, the overall prevalence of carbapenemase-producing E. coli was 27, with 7 carrying bla OXA48, 14 carrying bla NDM , and 6 carrying bla VIM . Notably, no strains were positive for bla KPC but a high prevalence rate of mcr genes were detected. mcr-1, mcr-2, mcr-3, and mcr-4 genes were detected among 3, 2, 21, and 3 strains, respectively. Conclusion The results indicate that camels in Egypt may be a primary source of anti-microbial resistance (AMR) E. coli, which could potentially be transmitted directly to humans or through the food chain.

Background: The resurgence of colistin has become critical in combating multidrug-resistant Gram-negative bacteria. However, the emergence of mobilized colistin resistance (mcr) genes presents a crucial global challenge, particularly in the Arab world, which includes regions with unique conditions and ongoing conflicts in some parts. Methods: To address this issue, a systematic review was conducted using multiple databases, including Cochrane, PubMed, Scopus, Web of Science, and Arab World Research Source. Results: A total of 153 studies were included, revealing substantial heterogeneity in the prevalence of mcr genes across 15 Arab countries, with notable findings indicating that Egypt and Lebanon reported the highest number of cases. The analysis indicated that the most prevalent sequence types were ST10, ST101, and ST1011, all of which are Escherichia coli strains linked to significant levels of colistin resistance and multiple antimicrobial resistance profiles. Conclusions: By analyzing the diverse findings from different Arab countries, this review lays a critical foundation for future research and highlights the necessity for enhanced surveillance and targeted interventions to address the looming threat of colistin resistance in the region. Systematic review registration: PROSPERO CRD42024584379.

Background: Camels harbouring multidrug-resistant Gram-negative bacteria are capable of transmitting various microorganisms to humans. This study aimed to determine the distribution of anti-microbial resistance among Escherichia coli (E. coli) isolated from the feces of apparently healthy camels in Egyptian abattoirs. Additionally, we sought to characterize Shiga toxin-producing E. coli (STEC) strains, assess their virulence potential, and investigate the possibility of camels spreading carbapenem- and colistin-resistant E. coli. Methods: 121 fecal swaps were collected from camels in different abattoirs in Egypt. Isolation and identification of E. coli were performed using conventional culture techniques and biochemical identification. All isolates obtained from the examined samples underwent genotyping through polymerase chain reaction (PCR) of the Shiga toxin-encoding genes (Stx1 and Stx2), the carbapenemase-encoding genes (blaKPC, blaOXA−48, blaNDM, and blaVIM), and the mcr genes for mcr-1 to mcr-5. Result: Bacteriological examination revealed 75 E. coli isolates. PCR results revealed that one strain (1.3%) tested positive for Stx1, and five (6.6%) were positive for Stx2. Among the total 75 strains of E. coli, the overall prevalence of carbapenemase-producing E. coli was 27, with 7 carrying blaOXA48, 14 carrying blaNDM, and 6 carrying blaVIM. Notably, no strains were positive for blaKPC but a high prevalence rate of mcr genes were detected. mcr-1, mcr-2, mcr-3, and mcr-4 genes were detected among 3, 2, 21, and 3 strains, respectively. Conclusion: The results indicate that camels in Egypt may be a primary source of anti-microbial resistance (AMR) E. coli, which could potentially be transmitted directly to humans or through the food chain. [ABSTRACT FROM AUTHOR]

The emergence of mobilized colistin resistance (mcr) genes has raised significant concerns as they pose a public health issue. The prevalence of mcr genes, particularly the newly discovered mcr-9 gene, in non-typhoidal Salmonella (NTS) isolates remains unclear. We characterized mcr-9.1-producing NTS isolates from China. Among 7,106 NTS isolates from diarrhea cases in 32 provinces during 2010–2020, 11 mcr-9.1-producing isolates were identified and were all not resistant to colistin. Five isolates belonged to Salmonella Thompson and sequence type (ST) 26, two belonged to Salmonella Typhimurium and ST34, two belonged to Salmonella Typhimurium and ST36, and two belonged to Salmonella 1,4,[5],12:i:- and ST34. Plasmids harboring mcr-9.1 tended to possess the IncHI2 backbone and were ~ 300 kb long. All mcr-9.1 genes shared the same flanking sequence, rcnR-rcnA-pcoS-IS903-mcr-9.1-wbuC. According to the NCBI data, we found that NTS serves as the primary host of mcr-9.1, although the prevalence of specific serotypes differed between domestic and international settings. Notably, most data came from developed countries, such as the USA. mcr-9.1 tended to be transferred as a gene cassette or to be mobilized by a conjugational plasmid in multiple bacteria across humans, animals, and the environment. Furthermore, mcr-9.1 frequently co-existed and was co-transferred with various genes encoding resistance to first-line drugs, reducing the effectiveness of available therapeutic options. In summary, although mcr-9 does not mediate colistin resistance, it can silently spread with some genes encoding resistance to first-line drugs, and therefore warrants research attention. [ABSTRACT FROM AUTHOR]

Background and Aim: Since first reported in 2015, the mobile colistin resistance (mcr-1) gene has been found in increasing numbers worldwide. However, only a few studies have been carried out in Morocco. Herein, we aimed to investigate the prevalence of colistin resistance and mcr-like genes among Enterobacteriaceae clinical isolates from the North-West of Morocco. Materials and Methods: The prevalence of colistin resistance was investigated among 338 Enterobacteriaceae clinical isolates. These isolates were collected from Tangier and Tetouan cities between December 2020 and May 2021. The isolates included Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), Enterobacterspp, Citrobacter freundii (C. freundii), and Proteus mirabilis (P. mirabilis). Antibacterial susceptibility tests were performed using disc diffusion assay and minimal inhibitory concentrations (MIC). All isolates that were found resistant to colistin were subjected to PCR and sequencing techniques to screen them for the presence of mcr-like genes (mcr-1 to mcr-5). Results: 22.78% of isolates were multidrug-resistant (MDR), among which 57.14% of P. mirabilis isolates, 30% of Enterobacter spp isolates, 22.22% of K. pneumoniae isolates, and 22.05% of E. coli isolates. Colistin resistance was found in 51 of 338 isolates, including 33 E. coli, 11 K. pneumoniae, and 7 P. mirabilis. The mcr-1 gene was detected in 3 E. coli isolates. Mcr-2 to mcr-5 genes were absent in this study. Sequencing of PCR amplicons revealed 99–100% similarity to mcr-1 gene. Conclusion: This is the first study conducted in Morocco to investigate the prevalence of colistin resistance among clinical isolates, and it has revealed the first three mcr-1 genes circulating in Morocco. This could lead to the dissemination of these genes throughout Morocco. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance (AMR) is a global threat that requires serious attention, particularly when it is developed against colistin, which is considered one of the 'last resort' antibiotics in the poultry industry. This study aimed to investigate the AMR profile of Enterobacteriaceae isolates from different poultry species, detect colistin resistance and investigate the existence of mcr genes in multi and extreme-resistant isolates. A total of 233 birds, chickens, ducks, turkeys, and quails, of various ages and breeds were collected from several localities of the Sharkia governorate and analyzed bacteriologically. The disc diffusion and E-test assays scrutinized the patterns of antibiotic, multidrug-resistant (MDR), and colistin resistance. The PCR assay was carried out to detect the mcr variants. Bacteriological examination revealed the incidence of 42.3% (99/233) of different Enterobacteriaceae members with a high predominance of E. coli, Salmonella, and Klebsiella species. Disc diffusion findings disclosed that 78.78% of isolates were resistant to colistin but E-test detected 19.19% only. Observed colistin resistance was strongly linked to the distribution of plasmid mcr-operons. The mcr 1, 2, 3, 4, and 7.1 genes were detected in 42.1, 63.15, 57.89, 52.63, and 47.36% of the phenotypic resistant isolates, and about 36.84% harbored at least four mcr clusters. However, the mcr5 gene was not discovered. The statistical assessment revealed a significant association between colistin resistance and MDR (p≤0.05). Moreover, there was a strong correlation between Mcr-abundance and doxycycline, fosfomycin, beta-lactams, imipenem, and tobramycin resistances. In conclusion, this study highlights the alarming occurrence of colistin-resistant Enterobacteriaceae in various poultry aspects. An urgent strategy must be adopted to avert the spread of this phenomenon. [ABSTRACT FROM AUTHOR]

Multi-drug resistance poses a serious threat to the public health worldwide. The situation becomes worse when multidrug-resistant bacteria develop resistance against last resort antibiotics such as colistin attributed to plasmid-borne mcr genes. Humans and non-human animals including pigs and chickens are the main reservoirs of these mcr genes harboring bacteria which have now disseminated globally, thus, causing difficulties in treating bacterial infections. Several mcr-gene-containing bacterial (MGCB) species have been found in diverse ecosystems, including aquatic, soil, botanical, wildlife, animal, and public environments. Environmental samples have shown to contain the mcr-1, mcr-2, mcr-3, mcr-5, mcr-7, and mcr-8 genes variants. The genes are found in Escherichia coli, Enterobacter, Klebsiella, Proteus, Salmonella, Citrobacter, Pseudomonas, Acinetobacter, Kluyvera, Aeromonas, Providencia, and Raulotella isolates. The routes of transmission of MGCB are contact with reservoirs that contain mcr, consumption of contaminated animal-/plant-based foods or water, trade and travel that involve animal-/plant-based foods. An updated and precise estimation of prevelance as well as mechanism of colistin resistance mediated by mcr genes is inevitable to regulate the spread of colistin resistance by implementing effective strategies. Hence, this review presents a comprehensive overview of epidemiology and the various mechanisms of colistin resistance that are currently not clearly understood. [ABSTRACT FROM AUTHOR]

Antibiotic resistance has emerged as a significant global public health issue, driven by the rapid adaptation of microorganisms to commonly prescribed antibiotics. Colistin, previously regarded as a last-resort antibiotic for treating infections caused by Gram-negative bacteria, is increasingly becoming resistant due to chromosomal mutations and the acquisition of resistance genes carried by plasmids, particularly the mcr genes. The mobile colistin resistance gene (mcr-1) was first discovered in E. coli from China in 2016. Since that time, studies have reported different variants of mcr genes ranging from mcr-1 to mcr-10, mainly in Enterobacteriaceae from various parts of the world, which is a major concern for public health. The co-presence of colistin-resistant genes with other antibiotic resistance determinants further complicates treatment strategies and underscores the urgent need for enhanced surveillance and antimicrobial stewardship efforts. Therefore, understanding the mechanisms driving colistin resistance and monitoring its global prevalence are essential steps in addressing the growing threat of antimicrobial resistance and preserving the efficacy of existing antibiotics. This review underscores the critical role of colistin as a last-choice antibiotic, elucidates the mechanisms of colistin resistance and the dissemination of resistant genes, explores the global prevalence of mcr genes, and evaluates the current detection methods for colistin-resistant bacteria. The objective is to shed light on these key aspects with strategies for combating the growing threat of resistance to antibiotics.

ABSTRACT Antibiotic resistance has become a worldwide public health and biosafety problem. The clinical efficacy of colistin was jeopardized by the report of the first mobile colistin resistance (mcr) gene, and subsequently, the mcr-gene family of mcr-1 to mcr-10 has been identified. Cronobacter is an emerging foodborne opportunistic pathogen, which can cause neonatal meningitis, bacteremia, and necrotizing enterocolitis (NEC) by contaminating food. However, the entire picture of foodborne Cronobacter carriage of the mcr genes is not known. Here, we investigated the mcr genes of Cronobacter isolates (N = 877) by whole-genome sequencing. We found 133 of 877 previously undescribed Cronobacter isolates carrying mcr genes. Further genomic analysis revealed that these mcr genes mainly belonged to the mcr-9 and mcr-10. Genomic analysis of the flanking structures of mcr genes revealed that two core flanking structures were prevalent in foodborne Cronobacter isolates, and the flanking structure carrying IS1R was found for the first time in this study. These findings suggest that foodborne Cronobacter isolates carrying the mcr genes already pose a threat to human health. IMPORTANCE Cronobacter is an emerging foodborne opportunistic pathogen, which can cause neonatal meningitis, bacteremia, and NEC by contaminating food. However, the entire picture of foodborne Cronobacter carriage of the mcr genes is not known. Here, we investigated the mcr genes of Cronobacter isolates by whole-genome sequencing and found 133 previously undescribed Cronobacter isolates carrying mcr genes. Further genomic analysis revealed that these mcr genes mainly belonged to the mcr-9 and mcr-10. Genomic analysis of the flanking structures of mcr genes revealed that two core flanking structures were prevalent in foodborne Cronobacter isolates, and the flanking structure carrying IS1R was found for the first time in this study.

Abstract Colistin is frequently used as a growth factor or treatment against infectious bacterial diseases in animals. The Veterinary Division of the European Medicines Agency (EMA) restricted colistin use as a second-line treatment to reduce colistin resistance. In 2020, 282 faecal samples were collected from chickens, cattle, sheep, goats, and pigs in the south of France. In order to track the emergence of mobilized colistin resistant (mcr) genes in pigs, 111 samples were re-collected in 2021 and included pig faeces, food, and water from the same location. All samples were cultured in a selective Lucie Bardet Jean-Marc Rolain (LBJMR) medium and colonies were identified using MALDI-TOF mass spectrometry and then antibiotic susceptibility tests were performed. PCR and Sanger sequencing were performed to screen for the presence of mcr genes. The selective culture revealed the presence of 397 bacteria corresponding to 35 different bacterial species including Gram-negative and Gram-positive. Pigs had the highest prevalence of colistin-resistant bacteria with an abundance of intrinsically colistin-resistant bacteria and from these samples one strain harbouring both mcr-1 and mcr-3 has been isolated. The second collection allowed us to identify 304 bacteria and revealed the spread of mcr-1 and mcr-3 in pigs. In the other samples, naturally, colistin-resistant bacteria were more frequent, nevertheless the mcr-1 variant was the most abundant gene found in chicken, sheep, and goat samples and one cattle sample was positive for the mcr-3 gene. Animals are potential reservoir of colistin-resistant bacteria which varies from one animal to another. Interventions and alternative options are required to reduce the emergence of colistin resistance and to avoid zoonotic transmissions.

Simple Summary: The extensive use of colistin in livestock is recognized as the main cause of the emergence of colistin resistance in Gram-negative bacteria. This phenomenon represents a public health concern, as colistin is one of the last-resort antibiotics against multidrug-resistant deadly infections in human medicine. In the present survey, DNA extracted from cloacal swabs from 195 broiler chickens in Tunisia was tested by PCR for the ten mobilized colistin resistance (mcr) genes known so far. Of the 195 animals tested, 81 (41.5%) were mcr-1 positive. These results confirm the urgent nature of antimicrobial resistance in the Tunisian poultry sector and suggest the need for cautious use of colistin in the veterinary field. Colistin is a polymyxin antibiotic that has been used in veterinary medicine for decades, as a treatment for enterobacterial digestive infections as well as a prophylactic treatment and growth promoter in livestock animals, leading to the emergence and spread of colistin-resistant Gram-negative bacteria and to a great public health concern, considering that colistin is one of the last-resort antibiotics against multidrug-resistant deadly infections in clinical practice. Previous studies performed on livestock animals in Tunisia using culture-dependent methods highlighted the presence of colistin-resistant Gram-negative bacteria. In the present survey, DNA extracted from cloacal swabs from 195 broiler chickens from six farms in Tunisia was tested via molecular methods for the ten mobilized colistin resistance (mcr) genes known so far. Of the 195 animals tested, 81 (41.5%) were mcr-1 positive. All the farms tested were positive, with a prevalence ranging from 13% to 93%. These results confirm the spread of colistin resistance in livestock animals in Tunisia and suggest that the investigation of antibiotic resistance genes by culture-independent methods could be a useful means of conducting epidemiological studies on the spread of antimicrobial resistance. [ABSTRACT FROM AUTHOR]

ABSTRACT Antimicrobial resistance is an increasing threat to human and animal health. Due to the rise of multi-, extensive, and pandrug resistance, last resort antibiotics, such as colistin, are extremely important in human medicine. While the distribution of colistin resistance genes can be tracked through sequencing methods, phenotypic characterization of putative antimicrobial resistance (AMR) genes is still important to confirm the phenotype conferred by different genes. While heterologous expression of AMR genes (e.g., in Escherichia coli) is a common approach, so far, no standard methods for heterologous expression and characterization of mcr genes exist. E. coli B-strains, designed for optimum protein expression, are frequently utilized. Here, we report that four E. coli B-strains are intrinsically resistant to colistin (MIC 8–16 μg/mL). The three tested B-strains that encode T7 RNA polymerase show growth defects when transformed with empty or mcr-expressing pET17b plasmids and grown in the presence of IPTG; K-12 or B-strains without T7 RNA polymerase do not show these growth defects. E. coli SHuffle T7 express carrying empty pET17b also skips wells in colistin MIC assays in the presence of IPTG. These phenotypes could explain why B-strains were erroneously reported as colistin susceptible. Analysis of existing genome data identified one nonsynonymous change in each pmrA and pmrB in all four E. coli B-strains; the E121K change in PmrB has previously been linked to intrinsic colistin resistance. We conclude that E. coli B-strains are not appropriate heterologous expression hosts for identification and characterization of mcr genes. IMPORTANCE Given the rise in multidrug, extensive drug, and pandrug resistance in bacteria and the increasing use of colistin to treat human infections, occurrence of mcr genes threatens human health, and characterization of these resistance genes becomes more important. We show that three commonly used heterologous expression strains are intrinsically resistant to colistin. This is important because these strains have previously been used to characterize and identify new mobile colistin resistance (mcr) genes. We also show that expression plasmids (i.e., pET17b) without inserts cause cell viability defects when carried by B-strains with T7 RNA polymerase and grown in the presence of IPTG. Our findings are important as they will facilitate improved selection of heterologous strains and plasmid combinations for characterizing AMR genes, which will be particularly important with a shift to Culture-independent diagnostic tests where bacterial isolates become increasingly less available for characterization.

Background: Antimicrobial resistance (AMR) is a global threat that requires serious attention, particularly when it is developed against colistin, which is considered one of the ‘last-resort’ antibiotics for curing an infection. This study aimed to investigate the AMR profile of the Klebsiella (K.) pneumoniae clinical isolates and to obtain the comprehensive characteristics of the carbapenemases among the carbapenem-resistant K. pneumoniae (CR-KP) when isolated. In addition, to detect the colistin resistance and investigate the MCR genes in the clinical K. pneumoniae isolates for the first time in Jordan. Methods: A total of 179 K. pneumoniae isolates were cultured and they were confirmed using the VITEK 2 system and PCR. The antibiotic susceptibilities, extended-spectrum beta-lactamase (ESβL), multidrug-resistant (MDR), and CR-KP were determined by using the VITEK 2 system, disc diffusion, and the minimum inhibitory concentration (MIC) test. PCR was performed to detect the MCR and carbapenemase genes. Results: The rates of ESβL, MDR, and CR-KP were 48 %, 62 %, and 12.8 %, respectively. High colistin resistance of 49.7 % (89/179) was found. Only one MCR-1 (1.1 %) out of the 89 colistin resistance isolates was detected. Many of the isolates harbored the ESβL genes. In particular, the carbapenem genes were detected in 26 isolates, with 46 % KPC enzyme genes (12/26), 23 % IMP genes (6/26), 19 % OXA-48 genes (5/26), 11.5 % NDM-1 genes (3/26) but no VIM gene was found. The statistical analyses revealed a significant association between colistin resistance and MDR (P ≤ 0.05, Chi-square test). An association between colistin resistance and the Piperacillin, Ceftazidime, Cefpodoxime, Imipenem, Aztreonam, and Tobramycin resistance was noted. Conclusion: The study’s findings demonstrated the presence of the MCR-1 gene in the K. pneumoniae clinical isolates for the first time in Jordan and indicated that the KPC and IMP encoded carbapenemases were the most prevalent K. pneumoniae carbapenemases in Jordan patients.

ABSTRACT: Objectives: Colistin is considered a last-resort antibiotic against carbapenem-resistant isolates. Currently, this antibiotic is facing the emergence of mobilised colistin resistance (mcr) genes, which confer colistin resistance. This study conducted genomic characterisation of an atypical multidrug-resistant Escherichia coli harbouring two mcr genes in France. Samples collected from a pig farm in Avignon (Vaucluse department) were subjected to molecular screening targeting mcr variants. Methods: Samples were cultured on selective Lucie-Bardet-Jean-Marc-Rolain medium. Growing bacteria were identified using MALDI-TOF, followed by antibiotic susceptibility testing. Whole-genome sequencing and bioinformatic genome analysis were performed. Results: Selective culture of stools revealed the presence of an E. coli strain named Q4552 harbouring mcr-1.1 and mcr-3.5 genes, which is also resistant to 14 antibiotics. Genome sequencing and assembly yielded a complete and circular chromosome and eight different plasmids. Sequence analysis demonstrated an integration of a mobile genetic element carrying mcr-1.1 in the chromosome, whereas mcr-3.5 was in the plasmid and its resistome was composed of 22 resistance genes. The Q4552 strain was identified as an ST-843 clone that belonged to the clonal complex Cplx-568 and is the only ST type of this cplx-568 that has been isolated from animals, humans, and the environment. Conclusion: We report the first co-occurrence of mcr-1 and mcr-3 genes in France from a pathogenic E. coli isolated from a pig. Because this clone (ST-843) has been reported in zoonotic transmissions, programs to monitor the bacterium are urgently required to avoid its spread and zoonotic transmission to humans.

ABSTRACT Shewanella species have been identified as progenitors of several clinically important antibiotic resistance genes. The aim of our study was to analyze Shewanella baltica strains isolated from the gut contents of wild Atlantic mackerel (Scomber scombrus) for the presence of both known and novel variants of antibiotic resistance genes (ARGs), using Illumina-based whole-genome sequencing (WGS). Thirty-three S. baltica strains were isolated from Atlantic mackerel collected in the northern North Sea. WGS revealed the presence of several new variants of class C and class D beta-lactamases. Nearly 42% (14/33) of the strains carried the mobile colistin resistance gene mcr-4.3. To understand the genetic context of mcr-4.3, we determined the complete genome sequence of strain 11FHM2, using a combination of Oxford Nanopore- and Illumina-based sequencing. The complete genome sequence is 5,406,724 bp long, with one contig representing a chromosome of 5,068,880 bp and three contigs representing novel plasmids (pSBP1, 194,145 bp; pSBP2_mcr4, 86,727 bp; and pSBP3, 56,972 bp). Plasmid pSBP2_mcr4 contains the mobile colistin resistance gene mcr-4.3, as well as the mercury resistance operon merRPAT. Plasmid pSBP1 carries genes encoding resistance against copper, zinc, chromium, and arsenic. Plasmid pSBP3 does not carry any antibiotic or heavy metal resistance genes. Analysis of the flanking region of mcr-4.3 suggests that a phage integrase may be involved in the mobilization of mcr-4.3 in Shewanella spp. Our results provide insights into the mobile mcr-4.3 present in Shewanella spp. and highlight the importance of the marine environment in the emergence and dissemination of clinically important resistance genes. IMPORTANCE We identified two new plasmids in Shewanella baltica isolated from wild Atlantic mackerel (Scomber scombrus) collected from the northern North Sea, one plasmid carrying the mcr-4.3 gene for colistin resistance and the operon merRPAT for mercury resistance and the other carrying multiple heavy metal resistance genes. The marine environment has been recognized as a source of new resistance genes that are found in human pathogens. Selection pressure from heavy metals is seen in the marine environment, especially associated with human activities, such as waste discharge, mining, and in aquaculture settings. This would help maintain and disseminate these plasmids in the environment. Our study provides insights into the mobilization of colistin resistance genes in Shewanella spp. and highlights the importance of the marine environment in the emergence and dissemination of clinically important antibiotic resistance genes.

Colistin is frequently used as a growth factor or treatment against infectious bacterial diseases in animals. The Veterinary Division of the European Medicines Agency (EMA) restricted colistin use as a second-line treatment to reduce colistin resistance. In 2020, 282 faecal samples were collected from chickens, cattle, sheep, goats, and pigs in the south of France. In order to track the emergence of mobilized colistin resistant (mcr) genes in pigs, 111 samples were re-collected in 2021 and included pig faeces, food, and water from the same location. All samples were cultured in a selective Lucie Bardet Jean-Marc Rolain (LBJMR) medium and colonies were identified using MALDI-TOF mass spectrometry and then antibiotic susceptibility tests were performed. PCR and Sanger sequencing were performed to screen for the presence of mcr genes. The selective culture revealed the presence of 397 bacteria corresponding to 35 different bacterial species including Gram-negative and Gram-positive. Pigs had the highest prevalence of colistin-resistant bacteria with an abundance of intrinsically colistin-resistant bacteria and from these samples one strain harbouring both mcr-1 and mcr-3 has been isolated. The second collection allowed us to identify 304 bacteria and revealed the spread of mcr-1 and mcr-3 in pigs. In the other samples, naturally, colistin-resistant bacteria were more frequent, nevertheless the mcr-1 variant was the most abundant gene found in chicken, sheep, and goat samples and one cattle sample was positive for the mcr-3 gene. Animals are potential reservoir of colistin-resistant bacteria which varies from one animal to another. Interventions and alternative options are required to reduce the emergence of colistin resistance and to avoid zoonotic transmissions. [ABSTRACT FROM AUTHOR]

Olfa Dziri,1– 3 Raoudha Dziri,1 Allaaeddin A El Salabi,4,5 Alhussain A Alawami,4 Riadh Ksouri,6 Chedly Chouchani1– 3 1Laboratory of Microorganisms and Active Biomolecules, Faculty of Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia; 2Laboratory of Research in Sciences and Technology of Environment, Higher Institute of Sciences and Technologies of Environment of Borj Cédria, University of Carthage, Hammam-Lif, Tunisia; 3Joint Service Unit for Research Genomic Platform, Higher Institute of Environmental Sciences and Technologies of Environment of Borj Cédria, Center of Biotechnology of Borj Cédria, Hammam-Lif, Tunisia; 4Infection Control and Patient Safety Office, New Marwa Hospital, Benghazi, Libya; 5Department of Environmental Health, Faculty of Public Health, University of Benghazi, Benghazi, Libya; 6Laboratory of Aromatic and Medicinal Plants, Center of Biotechnology of Borj Cédria, Hammam-Lif, TunisiaCorrespondence: Chedly Chouchani Email chedly.chouchani@gmail.comAbstract: The current global dissemination of polymyxin E resistance constitutes a real public health threat because of the restricted therapeutic options. This review provides a comprehensive assessment of the epidemiology of polymyxin E–resistant bacteria, with special reference to colistin-resistant Gram-negative bacteria in Tunisia and neighboring countries, based on available published data to January 2020. We aimed to determine their prevalence by species and origin, shedding light on the different genes involved and illustrating their genetic support, genetic environment, and geographic distribution. We found that colistin resistance varies considerably among countries. A majority of the research has focused on Algeria (13 of 32), followed by Tunisia (nine of 32), Egypt (nine of 32), and Libya (one of 32). All these reports showed that colistin-resistant Gram-negative bacteria were dramatically disseminated in these countries, as well as in African wildlife. Moreover, high prevalence of these isolates was recorded from various sources (humans, animals, food products, and natural environments). Colistin resistance was mainly reported among Enterobacteriaceae, particularly Klebsiella pneumoniae and Escherichia coli. It was associated with chromosomal mutations and plasmid-mediated genes (mcr). Four mcr variants (mcr 1, mcr 2, mcr 3, and mcr8), mobilized by several plasmid types (IncHI2, IncP, IncFIB, and IncI2), were detected in these countries and were responsible for their rapid spread. Countrywide dissemination of high-risk clones was also observed, including E. coli ST10 and K. pneumoniae ST101 and ST11. Intensified efforts to raise awareness of antibiotic use and legalization thereon are required in order to monitor and minimize the spread of multidrug-resistant bacteria.Keywords: Gram-negative bacteria, polymyxin E resistance, chromosomal mutations, mcr genes, plasmids

Antimicrobial resistance (AMR) is a global threat that requires serious attention, particularly when it is developed against colistin, which is considered one of the 'last-resort' antibiotics for curing an infection. This study aimed to investigate the AMR profile of the Klebsiella (K.) pneumoniae clinical isolates and to obtain the comprehensive characteristics of the carbapenemases among the carbapenem-resistant K. pneumoniae (CR-KP) when isolated. In addition, to detect the colistin resistance and investigate the MCR genes in the clinical K. pneumoniae isolates for the first time in Jordan. A total of 179 K. pneumoniae isolates were cultured and they were confirmed using the VITEK 2 system and PCR. The antibiotic susceptibilities, extended-spectrum beta-lactamase (ESβL), multidrug-resistant (MDR), and CR-KP were determined by using the VITEK 2 system, disc diffusion, and the minimum inhibitory concentration (MIC) test. PCR was performed to detect the MCR and carbapenemase genes. The rates of ESβL, MDR, and CR-KP were 48 %, 62 %, and 12.8 %, respectively. High colistin resistance of 49.7 % (89/179) was found. Only one MCR-1 (1.1 %) out of the 89 colistin resistance isolates was detected. Many of the isolates harbored the ESβL genes. In particular, the carbapenem genes were detected in 26 isolates, with 46 % KPC enzyme genes (12/26), 23 % IMP genes (6/26), 19 % OXA-48 genes (5/26), 11.5 % NDM-1 genes (3/26) but no VIM gene was found. The statistical analyses revealed a significant association between colistin resistance and MDR (P ≤ 0.05, Chi-square test). An association between colistin resistance and the Piperacillin, Ceftazidime, Cefpodoxime, Imipenem, Aztreonam, and Tobramycin resistance was noted. The study's findings demonstrated the presence of the MCR-1 gene in the K. pneumoniae clinical isolates for the first time in Jordan and indicated that the KPC and IMP encoded carbapenemases were the most prevalent K. pneumoniae carbapenemases in Jordan patients. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the percentage of healthy veal calves carrying mcr-positive E. coli strains at the time of slaughter in France. Fecal samples were selectively screened for mcr-positive E. coli isolates using media supplemented with colistin. Screening for mcr genes was also carried out in E. coli isolates resistant to critically important antimicrobials used in human medicine recovered from the same fecal samples. Overall, 28 (16.5%) out of the 170 veal calves tested carried mcr-positive E. coli. As some calves carried several non-redundant mcr-positive strains, 41 mcr-positive E. coli were recovered. Thirty-one and seven strains were positive for mcr-1 and mcr-3 genes, respectively, while no strain was positive for the mcr-2 gene. Co-carriage of mcr-1 and mcr-3 was identified in three strains. All mcr-positive E. coli isolates, except one, were multidrug-resistant, with 56.1% being ciprofloxacin-resistant and 31.7% harboring blaCTX-M genes. All mcr-3-positive E. coli carried blaCTX-M genes, mainly blaCTX-M-55. This study highlights the high prevalence of mcr-positive E. coli strains in feces of veal calves at the time of slaughter. It also points out the multidrug (including ciprofloxacin) resistance of such strains and the co-occurrence of mcr-3 genes with blaCTX-M-55 genes. [ABSTRACT FROM AUTHOR]

Colistin resistance in bacteria has become a significant threat to food safety and public health, and its development was mainly attributed to the plasmid-mediated mcr genes. This study aimed to determine the global prevalence and molecular characteristics of mcr-producing Salmonella enterica isolates. A total of 2279 mcr-producing Salmonella genomes were obtained from the public database, which were disseminated in 37 countries from five continents worldwide, including Asia, Europe, America, Australia, and Africa. Human samples (39.5%; 900/2279) were the predominant sources of mcr-producing Salmonella isolates, followed by foods (32.6%), animals (13.7%), and environment (4.4%). Furthermore, 80 Salmonella serotypes were identified, and Typhimurium and 1,4,[5],12:i:- were the predominant serotypes, accounting for 18.3% and 18.7%, respectively. Twenty mcr variants were identified, and the most common ones were mcr-9.1 (65.2%) and mcr-1.1 (24.4%). Carbapenems-resistance gene blaNDM-1 and tigecycline-resistance gene tet(X4) were identified in one isolate, respectively. Phylogenetic results indicated that mcr-producing Salmonella fell into nine lineages (Lineages I-IX), and Salmonella Typhimurium, 1,4,[5],12:i:- and 4,[5],12:i:- isolates from different countries were mixed in Lineages I, II and III, suggesting that international spread occurred. These findings underline further challenges for the spread of Salmonella-bearing mcr genes. [ABSTRACT FROM AUTHOR]

Colistin, the last resort for multidrug and extensively drug-resistant bacterial infection treatment, was reintroduced after being avoided in clinical settings from the 1970s to the 1990s because of its high toxicity. Colistin is considered a crucial treatment option for Acinetobacter baumannii and Pseudomonas aeruginosa , which are listed as critical priority pathogens for new antibiotics by the World Health Organization. The resistance mechanisms of colistin are considered to be chromosomally encoded, and no horizontal transfer has been reported. Nevertheless, in November 2015, a transmissible resistance mechanism of colistin, called mobile colistin resistance (MCR), was discovered. Up to ten families with MCR and more than 100 variants of Gram-negative bacteria have been reported worldwide. Even though few have been reported from Acinetobacter spp. and Pseudomonas spp., it is important to closely monitor the epidemiology of mcr genes in these pathogens. Therefore, this review focuses on the most recent update on colistin resistance and the epidemiology of mcr genes among non-fermentative Gram-negative bacilli, especially Acinetobacter spp. and P. aeruginosa. [ABSTRACT FROM AUTHOR]

This work aimed to evaluate phenotypically and genotypically the colistin susceptibility of 85 Salmonella Infantis strains isolated in Italy from the broiler production chain, and to apply a whole-genome approach for the determination of genes conferring antimicrobial resistance (AMR). All isolates were tested by the broth microdilution method to evaluate the colistin minimum inhibitory concentrations (MICs). A multiplex PCR was performed in all isolates for the screening of mcr-1, mcr-2, mcr-3 mcr-4, mcr-5 genes and whole-genome sequencing (WGS) of six S. Infantis was applied. Three out of 85 (3.5%) S. Infantis strains were colistin resistant (MIC values ranged from 4 to 8 mg/L) and mcr-1 positive. The mcr-1.1 and mcr-1.2 variants located on the IncX4 plasmid were detected in three different colistin-resistant isolates. The two allelic variants showed identical sequences. All six isolates harbored blaCTXM-1, aac(6′)-Iaa and gyrA/parC genes, mediating, respectively, beta-lactam, aminoglycoside and quinolone resistance. The pESI-megaplasmid carrying tet(A) (tetracycline resistance), dfrA1, (trimethoprim resistance) sul1, (sulfonamide resistance) and qacE (quaternary ammonium resistance) genes was found in all isolates. To our knowledge, this is the first report of the mcr-1.2 variant described in S. Infantis isolated from broilers chickens. Our results also showed a low prevalence of colistin- resistance, probably due to a reduction in colistin use in poultry. This might suggest an optimization of biosecurity control both on farms and in slaughterhouses. [ABSTRACT FROM AUTHOR]

Background: Pets, especially cats and dogs, represent a great potential for zoonotic transmission, leading to major health problems. The purpose of this systematic review was to present the latest developments concerning colistin resistance through mcr genes in pets. The current study also highlights the health risks of the transmission of colistin resistance between pets and humans. Methods: We conducted a systematic review on mcr-positive bacteria in pets and studies reporting their zoonotic transmission to humans. Bibliographic research queries were performed on the following databases: Google Scholar, PubMed, Scopus, Microsoft Academic, and Web of Science. Articles of interest were selected using the PRISMA guideline principles. Results: The analyzed articles from the investigated databases described the presence of mcr gene variants in pets including mcr-1, mcr-2, mcr-3, mcr-4, mcr-5, mcr-8, mcr-9, and mcr-10. Among these articles, four studies reported potential zoonotic transmission of mcr genes between pets and humans. The epidemiological analysis revealed that dogs and cats can be colonized by mcr genes that are beginning to spread in different countries worldwide. Overall, reported articles on this subject highlight the high risk of zoonotic transmission of colistin resistance genes between pets and their owners. Conclusions: This review demonstrated the spread of mcr genes in pets and their transmission to humans, indicating the need for further measures to control this significant threat to public health. Therefore, we suggest here some strategies against this threat such as avoiding zoonotic transmission. [ABSTRACT FROM AUTHOR]

Mera Mohammed Galal Anan,1 Eman Ahmed El-Seidi,1 Marwa Salah Mostafa,1 Laila Ahmed Rashed,2 Doaa Mahdy El-Wakil1 1Department of Medical Microbiology and Immunology, Faculty of Medicine, Cairo University, Cairo, Egypt; 2Department of Biochemistry and Molecular Biology, Faculty of Medicine, Cairo University, Cairo, EgyptCorrespondence: Mera Mohammed Galal AnanDepartment of Medical Microbiology and Immunology, Faculty of Medicine, Cairo University, Kasr Al-Ainy St., Cairo, 11562, EgyptTel +20 1288866285Email mira.hassan36203@postgrad.kasralainy.edu.egPurpose: Colistin represents one of the last treatment options for infections caused by multi-drug resistant (MDR) Enterobacterales. The emergence of a plasmid-mediated mobile colistin resistance-1 (mcr-1) gene has raised serious concerns about its potential dissemination among bacteria.Methods: In this study, we evaluated the chromogenic medium, CHROMID® Colistin Resistance (COLR) agar, for the rapid detection of colistin-resistant Enterobacterales using broth microdilution (BMD) as a reference method. We also attempted to detect mcr-1, − 2, − 3, − 4, and − 5 genes, as well as the insertion sequence ISApl1 via polymerase chain reaction (PCR), followed by sequencing of mcr gene(s).Results: Among the 100 studied Enterobacterales isolates, 53% of them were colistin-resistant, with higher rate among Klebsiella pneumoniae (75%) as compared to Escherichia coli (44.4%). The COLR agar showed 83.2% sensitivity and 97.9% specificity for the detection of colistin resistance. Among colistin-resistant isolates, mcr-1 gene was only detected in four (7.5%) E. coli isolates. The ISApl1 was not found among mcr-1 positive isolates. Sequencing of mcr-1 gene revealed nucleotide sequence homogeneity with the wild-type mcr-1 gene in BLAST.Conclusion: The COLR agar is a promising phenotypic method for the detection of colistin-resistant Enterobacterales. Multiplex PCR followed by sequencing can be used for mcr genes’ detection and characterization.Keywords: colistin resistance, Enterobacterales, mcr genes, CHROMID® COLR agar, multiplex PCR, sequencing

Colistin, the last resort for multidrug and extensively drug-resistant bacterial infection treatment, was reintroduced after being avoided in clinical settings from the 1970s to the 1990s because of its high toxicity. Colistin is considered a crucial treatment option for Acinetobacter baumannii and Pseudomonas aeruginosa, which are listed as critical priority pathogens for new antibiotics by the World Health Organization. The resistance mechanisms of colistin are considered to be chromosomally encoded, and no horizontal transfer has been reported. Nevertheless, in November 2015, a transmissible resistance mechanism of colistin, called mobile colistin resistance (MCR), was discovered. Up to ten families with MCR and more than 100 variants of Gram-negative bacteria have been reported worldwide. Even though few have been reported from Acinetobacter spp. and Pseudomonas spp., it is important to closely monitor the epidemiology of mcr genes in these pathogens. Therefore, this review focuses on the most recent update on colistin resistance and the epidemiology of mcr genes among non-fermentative Gram-negative bacilli, especially Acinetobacter spp. and P. aeruginosa.

Colistin is a polymyxin antimicrobic mainly used to treat infection caused by multi-drug resistant Gram-negative bacteria. Mechanisms of colistin resistance are linked to the mobile colistin resistance (mcr) genes, which are transferable within mobile plasmids. Currently, there is limited research on the environmental dissemination of these genes. The behavioural and morphological characteristics of Apis mellifera L. make honey bees effective environmental bioindicators for assessing the prevalence of antimicrobial-resistant bacteria. This study aims to evaluate the colistin phenotypic and genotypic resistance in environmental Gram-negative bacteria isolated from foraging honey bees, across a network of 33 colonies distributed across the Emilia-Romagna region in Italy. Phenotypic resistances were determined through a microdilution assay using the minimum inhibitory concentration (MIC) with dilutions ranging from 0.5 μg/ml to 256 μg/ml. Strains with MIC values gather than 2 μg/ml were classified as resistant. Also, the identification of the nine mcr genes was carried out using two separate multiplex PCR assays. The study found that 68.5% of isolates were resistant and the genus with the higher resistance rates observed in Enterobacter spp. (84.5%). At least one mcr gene was found in 137 strains (53.3%). The most detected gene was mcr5 (35.3%), which was the most frequently detected gene in the seven provinces, while the least observed was mcr4 (4.8%), detected only in two provinces. These results suggested the feasibility of detecting specific colistin resistance genes in environmentally spread bacteria and understanding their distribution at the environmental level, despite their restricted clinical use. In a One-Health approach, this capability enables valuable environmental monitoring, considering the significant role of colistin in the context of public health. [Display omitted] • AMR environmental monitoring is essential to protect ecosystem health. • Honey bee colonies are crucial in environmental biomonitoring. • Colistin is an antimicrobic used to treat MDR Gram-negative bacteria. • 68.5% of isolates were colistin-resistant and mcr genes were found in 53.3% of them. • The most detected gene was mcr5 (35.3%), while the least found was mcr4 (4.8%). [ABSTRACT FROM AUTHOR]

With the rising incidences of antimicrobial resistance (AMR) and the diminishing options of novel antimicrobial agents, it is paramount to decipher the molecular mechanisms of action and the emergence of resistance to the existing drugs. Polymyxin, a cationic antimicrobial lipopeptide, is used to treat infections by Gram-negative bacterial pathogens as a last option. Though polymyxins were identified almost seventy years back, their use has been restricted owing to toxicity issues in humans. However, their clinical use has been increasing in recent times resulting in the rise of polymyxin resistance. Moreover, the detection of "mobile colistin resistance (mcr)" genes in the environment and their spread across the globe have complicated the scenario. The mechanism of polymyxin action and the development of resistance is not thoroughly understood. Specifically, the polymyxin-bacterial lipopolysaccharide (LPS) interaction is a challenging area of investigation. The use of advanced biophysical techniques and improvement in molecular dynamics simulation approaches have furthered our understanding of this interaction, which will help develop polymyxin analogs with better bactericidal effects and lesser toxicity in the future. In this review, we have delved deeper into the mechanisms of polymyxin-LPS interactions, highlighting several models proposed, and the mechanisms of polymyxin resistance development in some of the most critical Gram-negative pathogens. [ABSTRACT FROM AUTHOR]

Colistin is a polymyxin antibiotic that has been used in veterinary medicine for decades, as a treatment for enterobacterial digestive infections as well as a prophylactic treatment and growth promoter in livestock animals, leading to the emergence and spread of colistin-resistant Gram-negative bacteria and to a great public health concern, considering that colistin is one of the last-resort antibiotics against multidrug-resistant deadly infections in clinical practice. Previous studies performed on livestock animals in Tunisia using culture-dependent methods highlighted the presence of colistin-resistant Gram-negative bacteria. In the present survey, DNA extracted from cloacal swabs from 195 broiler chickens from six farms in Tunisia was tested via molecular methods for the ten mobilized colistin resistance (mcr) genes known so far. Of the 195 animals tested, 81 (41.5%) were mcr-1 positive. All the farms tested were positive, with a prevalence ranging from 13% to 93%. These results confirm the spread of colistin resistance in livestock animals in Tunisia and suggest that the investigation of antibiotic resistance genes by culture-independent methods could be a useful means of conducting epidemiological studies on the spread of antimicrobial resistance.

The WHO has classified carbapenem-resistant Enterobacteriaceae in most critical priority pathogens that pose a threat to human health. The present study investigated the prevalence of meropenem-resistant Escherichia coli (E. coli) in relation to its temporal variation in different seasons along with its resistance markers in sewage water. E. coli was selected on MacConkey agar containing meropenem (3 µg/mL). There were 27% of sites/sewage samples carrying meropenem-resistant E. coli. All E. coli were confirmed through the amplification of the uidA gene. All isolated E. coli were multidrug-resistant (MDR), and among them, 51% were extensively drug-resistant (XDR). An antibiogram determined against 15 antibiotics showed the highest resistance to ampicillin and cefotaxime (98% each) and lowest resistance to fosfomycin (2%). Phylogenetic groups and resistance gene analysis through PCR showed a significant co-occurrence of carbapenemases with extended spectrum beta lactamases (ESBLs), plasmid encoded quinolone, and colistin resistance genes. The higher number of resistance genes in E. coli isolates in community sewage indirectly indicate that these isolates circulate abundantly in the community. [ABSTRACT FROM AUTHOR]

Colistin-resistant bacteria harboring plasmid-mediated mcr genes are of concern as they may be a cause of serious nosocomial infections. It is hypothesized that cessation of colistin use as a feed additive for pigs will reduce the occurrence and distribution of mcr genes in farms. The aim of this study was to investigate this hypothesis by longitudinal monitoring and characterizing of mcr positive Escherichia coli (MCRPE) isolates after colistin was withdrawn on a central Thailand pig farm that previously had a high frequency of MCRPE. Colistin use ceased at the beginning of 2017, and subsequently 170 samples were collected from farrowing sows and suckling piglets (n = 70), wastewater (n = 50) and farm workers (n = 50) over a 3.5-year period. Bacteria were identified by MALDI-TOF mass spectrometry and minimal inhibitory concentrations were determined by broth microdilution. The antibiogram of mcr positive E. coli isolates was determined using the Vitek2 automated susceptibility machine, and multiplex and simplex PCRs were performed for mcr-1–8 genes. MCRPE containing either mcr-1 or mcr-3 were isolated from pigs throughout the investigation period, but with a declining trend, whereas MCRPE isolates were recovered from humans only in 2017. MCRPE were still being recovered from wastewater in 2020. Most MCRPE isolates possessed the virulence genes Stap, Stb, or Stx2e, reflecting pathogenic potential in pigs, and showed high rates of resistance to ampicillin, gentamicin and tetracycline. Pulsed-field gel electrophoresis and multi-locus sequence typing showed that diverse MCRPE clones were distributed on the farm. The study identified a decline of pathogenic MCRPE following withdrawal of colistin, with pigs being the primary source, followed by wastewater. However, short-term therapeutic usage of other antibiotics could enhance the re-occurrence of mcr-carrying bacteria. Factors including the environment, management, and gene adaptations that allow maintenance of colistin resistance require further investigation, and longer-term studies are needed.

Keywords: colistin resistance; enterobacteria; zoonotic agent; antimicrobial resistance (AMR); MCR genes EN colistin resistance enterobacteria zoonotic agent antimicrobial resistance (AMR) MCR genes 1 4 4 02/08/22 20220204 NES 220204 Currently, the use of colistin as a last-resort antibiotic in human medicine is highly compromised due to the continuous emergence of resistant enterobacteria with acquired determinants like plasmid-mediated resistance genes ( I mcr i ), mutations that activate the PmrAB system, or still unknown mechanisms. Since the I mcr-1 i plasmid-mediated colistin resistance gene was discovered in China in 2015 (Liu et al., [5]), numerous surveys have been performed worldwide to monitor the prevalence and spread of I mcr i in food animals. Among the 22 AMR genes identified in S. Derby CFSA231, only the I mcr-1 i gene was localized on the IncX4 type plasmid pCFSA231 while 20 chromosomal AMR genes, including four plasmid-mediated quinolone resistance (PMQR) genes, were mapped within a 64 kb I Salmonella i genomic island (SGI) like region. [Extracted from the article]

Abstract Background The global emergence of plasmid-mediated colistin resistance (Col-R) conferred by mcr genes in gram-negative rods (GNRs) has jeopardized the last treatment option for multidrug-resistant bacterial infections in humans. This study aimed to assess the emergence of mcr gene-mediated Col-R in GNRs isolated from humans and animals in Pakistan. Methods Animal and clinical specimens collected from various sources were prospectively analysed using standard microbiological procedures. Pathogens were identified using the API 20E and API 20NE systems (bioMerieux). Minimum inhibitory concentration (MIC) against colistin was determined using the MIC detection methods, and multiplex polymerase chain reaction (PCR) was used to amplify the mcr-1 to mcr-5 genes. Results We isolated 126 (88.1%) animal and 17 (11.9%) human Col-R phenotypes, among which there was a significant association (P 6 µg/mL and > 12 µg/mL for human and animal isolates, respectively. mcr genes were detected in 110 (76.9%) bacterial strains, of which 108 (98.2%) were mcr-1 and 2 (1.8%) were mcr-2. Conclusions The detection of a considerable number of mcr-1 and mcr-2 genes in animals is worrisome, as they are now being detected in clinical pathogens. The acquisition of mcr genes by colistin-susceptible bacteria could leave us in a post-antibiotic era.

Chongtao Du,1,* Yuyang Feng,1,* Guizhen Wang,2 Zhiyuan Zhang,1 Huimin Hu,1 Yu Yu,1 Jiayang Liu,1 Lihao Qiu,1 Hongtao Liu,1 Zhimin Guo,3 Jing Huang,3 Jiazhang Qiu1 1Key Laboratory of Zoonosis, Ministry of Education, College of Veterinary Medicine, Jilin University, Changchun 130062, People’s Republic of China; 2College of Food Engineering, Jilin Engineering Normal University, Changchun 130052, People’s Republic of China; 3Department of Clinical Laboratory, The First Hospital of Jilin University, Changchun 130021, People’s Republic of China*These authors contributed equally to this workCorrespondence: Jiazhang QiuCollege of Veterinary Medicine, Jilin University, No. 5333 Xi’an Road, Changchun 130062, People’s Republic of ChinaEmail qiujz@jlu.edu.cnJing HuangDepartment of Clinical Laboratory, The First Hospital of Jilin University, Changchun 130021, People’s Republic of ChinaEmail huangj@jlu.edu.cnObjective: A colistin-resistant Escherichia coli strain isolated from dog feces was characterized in this study.Methods and Results: A multiplex PCR assay was used to detect the presence of colistin-resistant mcr genes; it was found that E. coli QDFD216 co-harbored the mcr-1 and mcr-3 genes. Whole-genome sequencing and further bioinformatics analysis revealed that E. coli QDFD216 belonged to serotype O176:H11, fimH1311 type and ST132. The resistance genes blaCTX-M-14, mdfA, dfrA3, acrA, acrB, tolc, and sul3 were present in the chromosome. The mcr-1.1 and mcr-3.7 genes were located in two plasmids of different incompatibility groups. mcr-1.1 was carried by a IncX4-type plasmid within an typical IS 26-parA-mcr-1.1-pap2 cassette, while mcr-3.7 was encoded by an IncP1-type plasmid with a genetic structure of TnAs2-mcr-3.7-dgkA-IS 26. No additional antibiotic resistance genes were carried by either plasmid.Conclusion: This is the first report of an E. coli isolate co-harboring a mcr-1.1-carrying IncX4 plasmid and a mcr-3.7-carrying IncP1 plasmid. The evolution and mechanism of mcr gene co-existence need further study to assess its impact on public health.Keywords: colistin resistance, whole-genome sequencing, mcr genes, mcr-1, mcr-3

Jiayang Liu1 ,* Zhiyuan Zhang1 ,* Yuyang Feng,1 Huimin Hu,1 Yu Yu,1 Lihao Qiu,1 Hongtao Liu,1 Zhimin Guo,2 Jing Huang,2 Chongtao Du,1 Jiazhang Qiu1 1Key Laboratory of Zoonosis, Ministry of Education, College of Veterinary Medicine, Jilin University, Changchun 130062, People’s Republic of China; 2Department of Clinical Laboratory, The First Hospital of Jilin University, Changchun 130021, People’s Republic of China*These authors contributed equally to this workCorrespondence: Jiazhang Qiu; Chongtao DuKey Laboratory of Zoonosis, Ministry of Education, College of Veterinary Medicine, Jilin University, Changchun 130062, People’s Republic of ChinaEmail qiujz@jlu.edu.cn; duct@jlu.edu.cnBackground: The emergence and prevalence of plasmid-mediated colistin-resistant bacterial strains in recent years have raised great concerns in clinical medicine. It is urgently needed to develop a cheaper, faster, simpler, sensitive, and specific molecular detection method to identify and monitor the dissemination of the transferable resistant determinants.Methods and Results: Herein, eight pairs of primers were designed to set up a multiplex PCR method for the rapid and efficient determination of reported mcr genes. This assay can give results within 85 min (35 min for amplification and 50 min for electrophoresis). We validated the feasibility of this assay by testing the presence of mcr genes in 60 colistin-resistant isolates.Conclusion: Our multiplex PCR technique exhibits remarkable advantages in the light of clear identification, efficiency of amplification, as well as the time consuming for detection, and thus could be useful for the surveillance and epidemiological research of plasmid-mediated colistin resistance, particularly for the under-resourced laboratories.Keywords: multiplex PCR, colistin resistance, mcr genes

Colistin is an old antimicrobial that has been revitalized as last-resort treatment against multidrug-resistant (MDR) gram-negative bacterial infections. However, colistin has been widely used in agricultural production and veterinary medicine for decades, and the recent global dissemination of mobilized colistin resistance (mcr) genes from animals to humans seriously threats the clinical use of colistin. Most of the mcr-harboring isolates have been Enterobacteriaceae, such as Escherichia coli and Salmonella enterica which are common to animals and humans. An understanding of the origin, dissemination and transmission of mcr genes in bacteria common to animals and humans will facilitate the management of colistin use and relevant interventions to prevent further spread of resistance. This review aims to provide a comprehensive assessment of the global prevalence and transmission of mcr genes of animal and human commensal/pathogenic bacteria.

Abstract Background Antimicrobial resistance has become one of the most severe global threats to human and veterinary Medicine. colistin is an effective therapeutic agent against multi-drug-resistant pathogens. However, the discovery of transferable plasmids that confer resistance to colistin (mcr-1) has led to challenges in medical science. This study describes the role of wild birds in the harbouring and environmental spread of colistin-resistant bacteria, which could pose a potential hazard to human and animal health. Methods In total, 140 faecal samples from wild birds (migratory and resident birds) were tested. Twenty surface water samples were collected from the area in which wild bird trapping was conducted, and 50 human stool samples were collected from individuals residing near the surface water sources and farm buildings. Isolation and identification of Enterobacteriaceae and Pseudomonas aeruginosa from the different samples were performed using conventional culture techniques and biochemical identification. PCR amplification of the mcr genes was performed in all positive isolates. Sequencing of mcr-1 genes from three randomly selected E. coli carrying mcr-1 isolates; wild birds, water and humans was performed. Result The bacteriological examination of the samples showing isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca and P. aeruginosa. The results of multiplex PCR of the mcr genes revealed that E. coli was the most prevalent gram-negative bacterium harbouring the mcr genes, whereas a low prevalence was observed for K. pneumoniae. The prevalence of mcr-1 in resident birds, migratory birds, water sources and humans were 10.4, 20,16.6 and 9.6% while the prevalence of mcr-2 were 1.4, 3.6, 11.1 and 9.6%, respectively. Sequencing of the mcr-1 gene from the three E. coli carrying mcr-1 isolates indicated a possible correlation between the wild bird and surface water isolates. Conclusion The detection of mcr-1-positive bacteria in wild birds in Egypt indicates the possible environmental dissemination of this gene through bird activity. The impact of the interaction between domestic and wild animals on public health cannot be overlooked.

Plasmid-mediated quinolone resistance (PMQR) genes and mobile colistin resistance (MCR) genes in Escherichia coli ( E. coli ) have been widely identified, which is considered a global threat to public health. In the present study, we conducted an analysis of MCR genes ( mcr-1 , mcr-2 , mcr-3 , mcr-4 , and mcr-5 ) and PMQR genes [ qnrA , qnrB , qnrC , qnrD , qnrE1 , qnrVC , qnrS , aac(6')-Ib-cr , qepA , and oqxAB ] in E. coli from China, 1993-2019. From the 3,663 E. coli isolates examined, 1,613 (44.0%) tested positive for PMQR genes, either individually or in combination. Meanwhile, 262 isolates (7.0%) carried the MCR genes. Minimum inhibitory concentration (MIC) analyses of 17 antibiotics for the MCR gene-carrying strains revealed universal multidrug resistance. Resistance to polymyxin varied between 4 μg/mL and 64 μg/mL, with MIC50 and MIC90 at 8 μg/mL and 16 μg/mL, respectively. In addition, fluctuations in the detection rates of these resistant genes correlated with the introduction of antibiotic policies, host origin, temporal trends, and geographical distribution. Continuous surveillance of PMQR and MCR variants in bacteria is required to implement control and prevention strategies.

Escherichia coli ST131 is one of the high-risk multidrug-resistant clones with a global distribution and the ability to persist and colonize in a variety of niches. Carbapenemase-producing E. coli ST131 strains with the ability to resist last-line antibiotics (i.e., colistin) have been recently considered a significant public health. Colistin is widely used in veterinary medicine and therefore, colistin-resistant bacteria can be transmitted from livestock to humans through food. There are several mechanisms of resistance to colistin, which include chromosomal mutations and plasmid-transmitted mcr genes. E. coli ST131 is a great model organism to investigate the emergence of superbugs. This microorganism has the ability to cause intestinal and extraintestinal infections, and its accurate identification as well as its antibiotic resistance patterns are vitally important for a successful treatment strategy. Therefore, further studies are required to understand the evolution of this resistant organism for drug design, controlling the evolution of other nascent emerging pathogens, and developing antibiotic stewardship programs. In this review, we will discuss the importance of E. coli ST131, the mechanisms of resistance to colistin as the last-resort antibiotic against resistant Gram-negative bacteria, reports from different regions regarding E. coli ST131 resistance to colistin, and the most recent therapeutic approaches against colistin-resistance bacteria. [ABSTRACT FROM AUTHOR]

Lan-Lan Zhong,1,2,* Qian Zhou,3,* Cui-Yan Tan,3,* Adam P Roberts,4,5 Mohamed Abd El-Gawad El-Sayed Ahmed,1–2,6 Guanping Chen,1,2 Min Dai,7 Fan Yang,8 Yong Xia,9 Kang Liao,10 Yingjian Liang,3 Yongqiang Yang,1,11 Siyuan Feng,1,2 Xiaobin Zheng,3,* Guo-Bao Tian1,2,*1Program in Pathobiology, The Fifth Affiliated Hospital, Zhongshan School of Medicine, Sun Yat-Sen University, Guangdong 519000, People’s Republic of China; 2Ministry of Education, Key Laboratory of Tropical Diseases Control, Sun Yat-sen University, Guangzhou 510080, People’s Republic of China; 3Department of Respiratory Medicine, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai 519000, People’s Republic of China; 4Department of Tropical Disease Biology, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, UK; 5Centre for Drugs and Diagnostics, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK; 6Department of Microbiology and Immunology, Faculty of Pharmaceutical Sciences and Drug Manufacturing, Misr University for Science and Technology (MUST), Cairo, Egypt; 7School of Laboratory Medicine, Chengdu Medical College, Chengdu 610500, People’s Republic of China; 8Department of Microbiology, School of Basic Medical Science, Xinxiang Medical University, Xinxiang 453003, People’s Republic of China; 9Department of Clinical Laboratory Medicine, The Third Affiliated Hospital of Guangzhou Medical University, Guangzhou 510150, People’s Republic of China; 10Department of Clinical Laboratory, The First Affiliated Hospital of Sun Yat-Sen University, Guangzhou 510080, People’s Republic of China; 11School of Pharmaceutical Sciences (Shenzhen), Sun Yat-sen University, Guangzhou 510006, People’s Republic of China*These authors contributed equally to this workPurpose: The discovery of the plasmid-mediated colistin resistance genes, mcr, revealed a mechanism of transmission of colistin resistance, which is a major, global public health concern especially among individuals infected with carbapenem-resistant Gram-negative bacteria. To monitor the spread and epidemiology of mcr genes, a convenient and reliable method to detect mcr genes in clinical isolates is needed, especially in the primary care institutions. This study aimed to establish a restriction endonuclease-based multiplex loop-mediated isothermal amplification (multi-LAMP) assay to detect mcr genes (mcr-1 to mcr-5) harbored by colistin-resistant bacteria.Methods: A triple-LAMP assay for mcr-1, mcr-3, and mcr-4 and a double-LAMP assay for mcr-2 and mcr-5 were established. The sensitivity and specificity of the LAMP reactions were determined via electrophoresis and visual detection.Results: The sensitivity of the LAMP assay was 10-fold greater than that of PCR, with high specificity among the screened primers. Specific mcr genes were distinguished in accordance with band numbers and the fragment length of the digested LAMP amplification products. Furthermore, the LAMP assay was confirmed as a rapid and reliable diagnostic technique upon application for clinical samples, and the results were consistent with those of conventional PCR assay.Conclusion: The multi-LAMP assay is a potentially promising method to detect mcr genes and will, if implemented, help prevent infections by drug-resistant bacteria in primary-care hospitals due to rapid and reliable surveillance. To our knowledge, this is the first study to report the application of LAMP to detect mcr-2 to mcr-5 genes and the first time that multi-LAMP has been applied to detect mcr genes.Keywords: mcr genes, colistin resistance, multi-LAMP, rapid detection, enzyme digestion

Zahra Aghapour,1,2 Pourya Gholizadeh,3 Khudaverdi Ganbarov,4 Abed Zahedi Bialvaei,5 Suhad Saad Mahmood,6 Asghar Tanomand,7 Mehdi Yousefi,8 Mohammad Asgharzadeh,9 Bahman Yousefi,9 Hossein Samadi Kafil11Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; 2Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran; 3Tuberculosis and Lung Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; 4Department of Microbiology, Baku State University, Baku, Azerbaijan; 5Department of Microbiology, Iran University of Medical Sciences, Tehran, Iran; 6Department of Biotechnology, College of Science, University of Baghdad, Baghdad, Iraq; 7Department of Microbiology, Maragheh University of Medical Sciences, Maragheh, Iran; 8Stem Cell Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; 9Biotechnology Research Center, Tabriz University of Medical Sciences, Tabriz, IranAbstract: Colistin is an effective antibiotic for treatment of most multidrug-resistant Gram-negative bacteria. It is used currently as a last-line drug for infections due to severe Gram-negative bacteria followed by an increase in resistance among Gram-negative bacteria. Colistin resistance is considered a serious problem, due to a lack of alternative antibiotics. Some bacteria, including Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacteriaceae members, such as Escherichia coli, Salmonella spp., and Klebsiella spp. have an acquired resistance against colistin. However, other bacteria, including Serratia spp., Proteus spp. and Burkholderia spp. are naturally resistant to this antibiotic. In addition, clinicians should be alert to the possibility of colistin resistance among multidrug-resistant bacteria and development through mutation or adaptation mechanisms. Rapidly emerging bacterial resistance has made it harder for us to rely completely on the discovery of new antibiotics; therefore, we need to have logical approaches to use old antibiotics, such as colistin. This review presents current knowledge about the different mechanisms of colistin resistance.Keywords: colistin, Enterobacteriaceae, two-component system, lipid A, mcr genes

The aim of this study was to determine the percentage of healthy veal calves carrying mcr-positive E. coli strains at the time of slaughter in France. Fecal samples were selectively screened for mcr-positive E. coli isolates using media supplemented with colistin. Screening for mcr genes was also carried out in E. coli isolates resistant to critically important antimicrobials used in human medicine recovered from the same fecal samples. Overall, 28 (16.5%) out of the 170 veal calves tested carried mcr-positive E. coli. As some calves carried several non-redundant mcr-positive strains, 41 mcr-positive E. coli were recovered. Thirty-one and seven strains were positive for mcr-1 and mcr-3 genes, respectively, while no strain was positive for the mcr-2 gene. Co-carriage of mcr-1 and mcr-3 was identified in three strains. All mcr-positive E. coli isolates, except one, were multidrug-resistant, with 56.1% being ciprofloxacin-resistant and 31.7% harboring blaCTX-M genes. All mcr-3-positive E. coli carried blaCTX-M genes, mainly blaCTX-M-55. This study highlights the high prevalence of mcr-positive E. coli strains in feces of veal calves at the time of slaughter. It also points out the multidrug (including ciprofloxacin) resistance of such strains and the co-occurrence of mcr-3 genes with blaCTX-M-55 genes.

Colistin resistance in bacteria has become a significant threat to food safety and public health, and its development was mainly attributed to the plasmid-mediated mcr genes. This study aimed to determine the global prevalence and molecular characteristics of mcr-producing Salmonella enterica isolates. A total of 2279 mcr-producing Salmonella genomes were obtained from the public database, which were disseminated in 37 countries from five continents worldwide, including Asia, Europe, America, Australia, and Africa. Human samples (39.5%; 900/2279) were the predominant sources of mcr-producing Salmonella isolates, followed by foods (32.6%), animals (13.7%), and environment (4.4%). Furthermore, 80 Salmonella serotypes were identified, and Typhimurium and 1,4,[5],12:i:- were the predominant serotypes, accounting for 18.3% and 18.7%, respectively. Twenty mcr variants were identified, and the most common ones were mcr-9.1 (65.2%) and mcr-1.1 (24.4%). Carbapenems-resistance gene blaNDM-1 and tigecycline-resistance gene tet(X4) were identified in one isolate, respectively. Phylogenetic results indicated that mcr-producing Salmonella fell into nine lineages (Lineages I-IX), and Salmonella Typhimurium, 1,4,[5],12:i:- and 4,[5],12:i:- isolates from different countries were mixed in Lineages I, II and III, suggesting that international spread occurred. These findings underline further challenges for the spread of Salmonella-bearing mcr genes.