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There is scarce information concerning the role of sporadic clones in the dissemination of antimicrobial resistance genes (ARGs) within the nosocomial niche. We confirmed that the clinical Escherichia coli M19736 ST615 strain, one of the first isolates of Latin America that harbors a plasmid with an mcr-1 gene, could receive crucial ARG by transformation and conjugation using as donors critical plasmids that harbor bla CTX-M-15 , bla KPC-2 , bla NDM-5 , bla NDM-1 , or aadB genes. Escherichia coli M19736 acquired bla CTX-M-15 , bla KPC-2 genes, the maintenance pattern of the plasmids changed. In addition, when the evolved XDR- bla NDM-5 M19736 strains disseminated simultaneously the acquired conjugative plasmids in different combinations though selection was ceftazidime in all cases. Finally, we isolated and characterized the extracellular vesicles (EVs) from the native and evolved XDR- bla NDM-1 , and aadB genes, being only blaNDM-1 maintained at 100% on the 10th day of subculture. In addition, when the evolved MDR- E. coli M19736 acquired sequentially bla CTX-M-15 and bla NDM-1 genes, the maintenance pattern of the plasmids changed. In addition, when the evolved XDR- E. coli M19736 acquired in an ulterior step the paadB plasmid, a different pattern of the plasmid's maintenance was found. Interestingly, the evolved E. coli M19736 strains disseminated simultaneously the acquired conjugative plasmids in different combinations though selection was ceftazidime in all cases. Finally, we isolated and characterized the extracellular vesicles (EVs) from the native and evolved XDR- E. coli M19736 strains. Interestingly, EVs from the evolved XDR- E. coli M19736 harbored bla CTX-M-15 though the pDCAG1-CTX-M-15 was previously lost as shown by WGS and experiments, suggesting that EV could be a relevant reservoir of ARG for susceptible bacteria. These results evidenced the genetic plasticity of a sporadic clone of E. coli such as ST615 that could play a relevant transitional link in the clinical dynamics and evolution to multidrug/extensively/pandrug-resistant phenotypes of superbugs within the nosocomial niche by acting simultaneously as a vector and reservoir of multiple ARGs which later could be disseminated., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Carrera Páez, Olivier, Gambino, Poklepovich, Aguilar, Quiroga and Centrón.)

There is emerging evidence that food of animal origin may be responsible for the spread of multidrug resistant extraintestinal pathogenic Escherichia coli in the community. Here, we describe the emergence of colistin resistance gene, mcr-1, in a strain belonging to the dominant uropathogenic E. coli ST69 lineage. E. coli strain CFSAN061770 was isolated during monitoring of the popular Egyptian raw milk cheese, karish cheese, for the presence of colistin resistance. The complete genome of E. coli strain CFSAN061770 comprises a chromosome of 5,292,297 bp with a G + C content of 50.6%. Further, three plasmids named pEGY1-MCR-1, pEGY2 and pEGY3 of 228,947 bp, 103,234 bp and 87,012 bp were detected, respectively. Plasmid pEGY1-MCR-1 belongs to the IncHI2 incompatibility group and carries the colistin resistance mcr-1 gene flanked by two ISApl1 elements and forms a composite transposon. It mediates resistance to aminoglycosides (aadA1 and aadA2), phenicol (cmlA1 and floR), sulfonamides (sul3), and tetracycline (tet(A)), and these loci were found clustered in a multidrug resistant region. Plasmid pEGY3 carries a complex multiple resistance locus (CMR) (aph(3')-Ia, strA, strB, sul2, and bla TEM-1 ) encoding resistance to different classes of antibiotics. Interestingly, the closest plasmids to plasmid pEGY1-MCR-1 detected from the NCBI Blast search belonged to the incompatibility group IncHI2 and were from the Kingdom of Saudi Arabia and Qatar which suggests a dissemination of pEGY1-MCR-1-like plasmids in the Middle East. Most striking, and of great public health concern is that strain CFSAN061770 carries five virulence genes (iss, fimH, iutA, kpsMIII and kpsTIII) which were identified in clinical extraintestinal pathogenic E. coli. Besides that, it carries the astA gene, which codes for the enteroaggregative E. coli heat-stable toxin 1 (EAST1)., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Bacterial infections in immunocompromised patients are associated with a high mortality and morbidity rate. In this high-risk group, the presence of multidrug-resistant (MDR) bacteria, particularly bacteria that harbor a transferable antibiotic resistance gene, complicates the management of bacterial infections. In this study, we investigated the presence of the transferable colistin resistance mcr genes in patients with leukemia in Spain., Methods: 217 fecal samples collected in 2013-2015 from 56 patients with acute leukemia and colonized with MDR Enterobacteriaceae strains, were screened on September 2017 for the presence of the colistin resistance mcr genes (mcr-1 to -5) by multiplex PCR. mcr positive strains selected on LBJMR and MacConkey supplemented with colistin (2 μg/ml) media were phenotypically and molecularly characterized by antimicrobial susceptibility testing, minimum inhibitory concentration, multilocus sequence typing and plasmid characterization., Results: Among 217 fecal samples, 5 samples collected from 3 patients were positive for the presence of the mcr-1 colistin-resistance gene. Four Escherichia coli strains were isolated and exhibited resistance to colistin with MIC = 4 μg/ml. Other genes conferring the resistance to β-lactam antibiotics have also been identified in mcr-1 positive strains, including bla TEM-206 and bla TEM-98 . Three different sequence types were identified, including ST1196, ST140 and ST10. Plasmid characterization allowed us to detect the mcr-1 colistin resistance gene on conjugative IncP plasmid type., Conclusion: To the best of our knowledge, we have identified the mcr-1 gene for the first time in leukemia patients in Spain. In light of these results, strict measures have been implemented to prevent its dissemination., (Copyright © 2019 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.)

There is a global concern about the increasing resistance of bacterial pathogens to colistin, an antibiotic of last resort for the treatment of multidrug-resistant Gram-negative bacterial infections (e.g. carbapenemase-producing Enterobacteriaceae). In this study, an increasing prevalence of colistin resistance in raw and treated wastewater was demonstrated using a new developed SYBR Green-based real-time PCR assay for specific detection and quantification of the plasmid-mediated mcr-1 gene. Raw and treated wastewater samples were collected from a wastewater treatment plant in Girona (Spain) at two different time periods (November 2011-January 2012 and December 2016-February 2017). In both periods, the absolute abundance of the mcr-1 gene was significantly higher (P <0.05) in raw sewage samples, suggesting that conventional wastewater treatment reduces colistin-resistant bacteria. Moreover, the analysis revealed an increase from 1-2 orders of magnitude in the absolute abundance of mcr-1 between the studied periods (winter 2011 versus winter 2016, P <0.05), suggesting that colistin resistance has increased over time. This study gives evidence of the growing spread of mcr-1 and provides a real-time PCR assay for its rapid detection and quantification., (Copyright © 2017 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.)

One mcr-1-carrying Salmonella enterica serovar Indiana strain D90, was identified from 1320 Salmonella enterica isolates from poultry slaughterhouse in 2012 in China. The objective of this study was to verify the transferability of the mcr-1 gene and also completely characterize the sequence of the strain at the whole-genome level. Broth matting assays were carried out to detect the transferability and whole-genome sequencing (WGS) of S. enterica serovar Indiana D90 was performed using the PacBio RS II system. Open reading frames were assigned using Rapid Annotation using Subsystem Technology (RAST) and analysed by BLASTn and BLASTp. Salmonella Pathogenisity Islands (SPIs) were annotated by SPIFinder platform. The complete genome sequence of S. enterica serovar Indiana D90 contained a circular 4,779,514-bp chromosome and four plasmids. Genome analysis and sequencing revealed that 24 multi-drug resistance (MDR) genes were located on plasmids. The largest plasmid pD90-1, was found to be of an IncHI2/HI2A/Q1/N type that encoded a bla CTX-M-65 gene along with 20 additional antimicrobial resistance genes. A 60.5-kbp IncI2 plasmid pD90-2 contained a nikA-nikB-mcr-1 genetic structure, that can be successfully transferred to E. coli and S. enterica serovar Typhimurium at low transfer rates. Interestingly, comparative sequence analysis revealed the plasmids pD90-1 and pD90-2 showed considerable nucleotide similarity to pHNSHP45-2 and pHNSHP45, respectively. Moreover, the genome and the plasmid pD90-2 also showed high similarity to one carbapenem resistant S. enterica serovar Indiana strain, C629 and its plasmid pC629, respectively. This is the first report of the complete nucleotide sequence of one mcr-1-carrying MDR S. enterica serovar Indiana strain., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Addressing the emergence of antimicrobial resistance (AMR) poses a significant challenge in veterinary and public health. In this study, we focused on determining the presence, phenotypic background, and genetic epidemiology of plasmid-mediated colistin resistance (mcr) in Escherichia coli bacteria isolated from camels farmed in the United Arab Emirates (UAE). Fecal samples were collected from 50 camels at a Dubai-based farm in the UAE and colistin-resistant Gram-negative bacilli were isolated using selective culture. Subsequently, a multiplex PCR targeting a range of mcr-genes, plasmid profiling, and whole-genome sequencing (WGS) were conducted. Eleven of fifty camel fecal samples (22%) yielded colonies positive for E. coli isolates carrying the mcr-1 gene on mobile genetic elements. No other mcr-gene variants and no chromosomally located colistin resistance genes were detected. Following plasmid profiling and WGS, nine E. coli isolates from eight camels were selected for in-depth analysis. E. coli sequence types (STs) identified included ST7, ST21, ST24, ST399, ST649, ST999, and STdaa2. Seven IncI2(delta) and two IncX4 plasmids were found to be associated with mcr-1 carriage in these isolates. These findings represent the first identification of mcr-1-carrying plasmids associated with camels in the Gulf region. The presence of mcr-1 in camels from this region was previously unreported and serves as a novel finding in the field of AMR surveillance. [ABSTRACT FROM AUTHOR]

Addressing the emergence of antimicrobial resistance (AMR) poses a significant challenge in veterinary and public health. In this study, we focused on determining the presence, phenotypic background, and genetic epidemiology of plasmid-mediated colistin resistance (mcr) in Escherichia coli bacteria isolated from camels farmed in the United Arab Emirates (UAE). Fecal samples were collected from 50 camels at a Dubai-based farm in the UAE and colistin-resistant Gram-negative bacilli were isolated using selective culture. Subsequently, a multiplex PCR targeting a range of mcr-genes, plasmid profiling, and whole-genome sequencing (WGS) were conducted. Eleven of fifty camel fecal samples (22%) yielded colonies positive for E. coli isolates carrying the mcr-1 gene on mobile genetic elements. No other mcr-gene variants and no chromosomally located colistin resistance genes were detected. Following plasmid profiling and WGS, nine E. coli isolates from eight camels were selected for in-depth analysis. E. coli sequence types (STs) identified included ST7, ST21, ST24, ST399, ST649, ST999, and STdaa2. Seven IncI2(delta) and two IncX4 plasmids were found to be associated with mcr-1 carriage in these isolates. These findings represent the first identification of mcr-1-carrying plasmids associated with camels in the Gulf region. The presence of mcr-1 in camels from this region was previously unreported and serves as a novel finding in the field of AMR surveillance.

Objectives: This study aimed to explore mechanism of colistin resistance amongst Klebsiella pneumoniae isolates through plasmid mediated mcr-1 gene in Pakistan. Carbapenem and Colistin resistant K. pneumoniae isolates (n = 34) stored at − 80 °C as part of the Aga Khan University Clinical Laboratory strain bank were randomly selected and subjected to mcr-1 gene PCR. To investigate mechanisms of resistance, other than plasmid mediated mcr-1 gene, whole genome sequencing was performed on 8 clinical isolates, including 6 with colistin resistance (MIC > 4 μg/ml) and 2 with intermediate resistance to colistin (MIC > 2 μg/ml). Results: RT-PCR conducted revealed absence of mcr-1 gene in all isolates tested. Whole genome sequencing results revealed modifications in Lipid A-Ara4N pathway. Modifications in Lipid A-Ara4N pathway were detected in ArnA_ DH/FT, UgdH, ArnC and ArnT genes. Mutation in ArnA_ DH/FT gene were detected in S3, S5, S6 and S7 isolates. UgdH gene modifications were found in all isolates except S3, mutations in ArnC were present in all except S1, S2 and S8 and ArnT were detected in all except S4 and S7. In the absence of known mutations linked with colistin resistance, lipid pathway modifications may possibly explain the phenotype resistance to colistin, but this needs further exploration. [ABSTRACT FROM AUTHOR]

Present study characterized five Escherichia coli co-expressing ESBL and MCR-1 recovered from food, food-producing animals, and companion animals in China. Antimicrobial susceptibility tests, conjugation experiments, and plasmid typing were performed. Whole genome sequencing (WGS) was undertaken for all five isolates using either PacBio RS II or Illumina HiSeq 2500 platforms. The cefotaxime and colistin resistance encoded by bla CTX–M and mcr-1 genes, respectively, was transferable by conjugation either together or separately for all five strains. Interestingly, the ESBL and mcr-1 genes could be co-selected by cefotaxime, while the colistin only selected the mcr-1 -carrying plasmids during the conjugation experiments. Five E. coli sequence types (ST88, ST93, ST602, ST162, and ST457) were detected. Although diverse plasmid profiles were identified, IncI2, IncFIB, and IncFII plasmid types were predominant. These five clonally unrelated isolates harbored the mcr-1 gene located on similar plasmid backbones, which showed high nucleotide similarity to plasmid pHNSHP45. The mcr-1 gene can be co-transmitted with bla CTX–M genes through IncI2 plasmids with or without IS Apl1 in our study. Characterization of these co-existence ESBL and mcr-1 isolates extends our understanding on the dissemination of these resistance markers among bacteria of diverse origins. [ABSTRACT FROM AUTHOR]

Background: The mcr-1 gene has been widely reported in both bacterial chromosomes and plasmids, while its stability in these genetic materials is not well understood.Objectives: Our aim was to characterize the stability and dynamics of Tn6330 elements in both a plasmid and the chromosome in a single bacterial population.Methods: Plasmid-borne and chromosomal Tn6330 were characterized by PCR, conjugation, S1-PFGE, stability assay, single-molecule long-read sequencing and bioinformatics analysis.Results: Tn6330 was simultaneously detected in both a plasmid and the chromosome of a clinical Escherichia coli strain. The plasmid was found to comprise the IncFIB replicon and a phage-like replicon, as well as two integrons that harboured various mobile elements and resistance genes including mcr-1, floR, blaTEM-1b and strAB. Both plasmid-borne and chromosomal Tn6330 transposons could be re-organized into a circular intermediate that played a role in transmission of the mcr-1 gene. Tn6330 was found to be very stable in both the plasmid and chromosome after 30 passages of 12 h with or without colistin selective pressure. The decayed structure of Tn6330 in the genuine single DNA molecules of bacterial populations, although occurring at a very low frequency, could be detected for the first time, in which Tn6330 was degraded into a single ISApl1 element.Conclusions: Long-read sequencing technology is a good tool to study the evolution and stability of genetic elements in bacteria. The ultrastability of an mcr-1-encoding element in a bacterial plasmid and chromosome renders it unlikely to be eradicated quickly by the reduced use of colistin, and factors leading to the frequent demise of Tn6330 warrant further studies. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the prevalence and molecular characteristics of ESBL-producing Escherichia coli (ESBL-EC) in faecal samples from dairy cows in China.Methods: In total, 651 faecal samples were collected from cows distributed among the 10 provinces of China. Potential ESBL-EC isolates were cultured on selective medium. The clonal relatedness of the ESBL-EC isolates was assessed using MLST. WGS was conducted on 3 mcr-positive isolates and 14 additional randomly selected ESBL-EC isolates. Southern blot, S1-PFGE and conjugation were performed for mcr-1-carrying isolates. The genetic environment of the pMCR-JLF4 plasmid was also analysed.Results: In total, 290 unique ESBL-EC isolates were detected from 284 cows (43.6%). Alleles of CTX-M were observed in 94.1% (273/290) of all isolates. The most prevalent genotypes observed in this study were blaCTX-M-14, blaCTX-M-15, blaCTX-M-17 and blaCTX-M-55. Differentiation of 79 STs with a polyclonal structure was accomplished using MLST. Clonal complex 10 was the most prevalent major complex detected here. Furthermore, the mcr-1 gene was detected in three isolates. The complete sequence of the mcr-1-containing pMCR-JLF4 was determined. The plasmid was 66.7 kb in length, with a genetic structure of nikA-nikB-mcr-1-pap2. Conjugation analysis confirmed that the mcr-1 gene in pMCR-JLF4 was transferable without the assistance of the ISApl1 gene.Conclusions: The data presented here suggest high prevalence of ESBL-EC in Chinese cow farms. Furthermore, it was clearly demonstrated that commensal E. coli strains can be reservoirs of blaCTX-M genes, potentially contributing to the dissemination and transfer of the mcr-1 gene to pathogenic bacteria among cows. [ABSTRACT FROM AUTHOR]

Objectives: In Asian countries, blaCTX-M-55 is the second most common ESBL-encoding gene. blaCTX-M-55 frequently co-localizes with fosA and rmtB genes on epidemic plasmids, which remain sporadic outside Asia. During 2010-13, we investigated CTX-M-55-producing Escherichia coli isolates and their co-resistance to fosfomycin, aminoglycosides, fluoroquinolones and colistin as part of a global survey of ESBLs in animals in France. Methods: blaCTX-M-55, fosA, rmtB and plasmidic quinolone and colistin resistance genes were characterized by PCR, sequencing and hybridization experiments. Plasmids were classified according to their incompatibility groups and subtypes. Genotyping was performed by MLST and repetitive extragenic palindromic sequence-based PCR. Results: Twenty-one E. coli isolates from bovines (n = 16), dogs (n = 2), horses (n = 2) and a monkey harboured blaCTX -M-55, were MDR and belonged to ST744 (n = 9) and 10 other clones. blacTx-M-55 was mostly located on IncF (n = 19), but also on IncI1 (n = 2) plasmids. On IncF33:A1:B1 plasmids, blaCTX-M-55 co-localized with the rmtB and aac(6')-Ib genes and in one isolate with the fosA3 allele. Ten IncF46:A-:B20 plasmids, which were found in different clones from unrelated animals, also carried the mcr-3 gene. blaCTX-M-55-carrying IncF18:A-:B1 plasmids were found in different animal species from distinct locations and periods, and one additionally carried the fosA4 gene. One isolate harboured the mcr-1 gene, which did not co-localize with blaCTX-M-55. Conclusions: A large diversity of E. coli clones and plasmid types supported the spread of blaCTX-M-55, together with atypical resistance genes, in various animal species in France. fosA and rmtB genes are emerging among animals in Europe and this issue is of concern for public health. [ABSTRACT FROM AUTHOR]

Objectives: In Asian countries, blaCTX-M-55 is the second most common ESBL-encoding gene. blaCTX-M-55 frequently co-localizes with fosA and rmtB genes on epidemic plasmids, which remain sporadic outside Asia. During 2010-13, we investigated CTX-M-55-producing Escherichia coli isolates and their co-resistance to fosfomycin, aminoglycosides, fluoroquinolones and colistin as part of a global survey of ESBLs in animals in France.Methods: blaCTX-M-55, fosA, rmtB and plasmidic quinolone and colistin resistance genes were characterized by PCR, sequencing and hybridization experiments. Plasmids were classified according to their incompatibility groups and subtypes. Genotyping was performed by MLST and repetitive extragenic palindromic sequence-based PCR.Results: Twenty-one E. coli isolates from bovines (n = 16), dogs (n = 2), horses (n = 2) and a monkey harboured blaCTX-M-55, were MDR and belonged to ST744 (n = 9) and 10 other clones. blaCTX-M-55 was mostly located on IncF (n = 19), but also on IncI1 (n = 2) plasmids. On IncF33:A1:B1 plasmids, blaCTX-M-55 co-localized with the rmtB and aac(6')-Ib genes and in one isolate with the fosA3 allele. Ten IncF46:A-:B20 plasmids, which were found in different clones from unrelated animals, also carried the mcr-3 gene. blaCTX-M-55-carrying IncF18:A-:B1 plasmids were found in different animal species from distinct locations and periods, and one additionally carried the fosA4 gene. One isolate harboured the mcr-1 gene, which did not co-localize with blaCTX-M-55.Conclusions: A large diversity of E. coli clones and plasmid types supported the spread of blaCTX-M-55, together with atypical resistance genes, in various animal species in France. fosA and rmtB genes are emerging among animals in Europe and this issue is of concern for public health. [ABSTRACT FROM AUTHOR]

The article presents a study on isolation of the foodborne, Salmonella from food in China. Topics discussed include information on the screening of food samples for the presence of the mcr-1 gene using a quantitative Polymerase chain reaction method; discussions on the identification of Salmonella Typhimurium after phylogenetic analysis; and the information on the study reveals the presence of plasmids in the strains.

We hereby report the first characterization of mcr-3 gene from healthy animals in South Korea. Out of 636 E. coli isolates, collected between 2014- 2017, nine colistin resistant isolates were screened for the presence of mcr-1 and mcr-3 genes. Nine (1.4%) isolates had shown resistance for colistin and among them three and two isolates were mcr-1 harboring and mcr-3 harboring strains, respectively. All the colistin-resistant isolates were multidrug-resistant. mcr-1 and mcr-3 genes were confirmed to be transferred to a recipient E. coli J53 AZ R . [ABSTRACT FROM AUTHOR]

mcr-1.2 , an allelic variant of the transferable colistin resistance gene mcr-1 , was characterized in a colistin-resistant blood isolate of Escherichia coli . It was harbored by an IncX4-type plasmid (33,293 bp). Despite its low prevalence, the potentially worrying spread of the mcr-1 gene, particularly its mcr-1.2 variant, in Italy requires increasing surveillance. [ABSTRACT FROM AUTHOR]

Objective: Colistin is our last line of defense in the treatment of infections caused by multidrug-resistant gram-negative pathogens. However, resistance against colistin has been observed worldwide. In a recent study, a plasmid-mediated colistin resistance gene (mcr-1) was identified for the first time. The purpose of the present study was to conduct an in silico search for the mcr-1 gene and the plasmid harboring it in a cohort of human gut microbiomes, which have already been deposited in public metagenome databases in different geographies. Materials and Methods: The gut metagenomes of 344 Chinese and 145 European individuals were investigated. Each metagenome sample consisted of sequencing reads obtained from next-generation sequencing. Each DNA read was aligned against the entire mcr-1 and pHNSHP45 plasmid sequences using the BLASTn program. A nucleotide identity threshold of 95% similarity was set, and the reads aligned under that similarity were filtered out. Results: According to our investigation, 6 out of the 344 individuals in the Chinese cohort harbored the mcr-1 gene and close homologs of pHNSHP45 plasmid in their gut microbiota, whereas no related genetic elements were found in the European cohort. Conclusion: As the human gut microbiome is one of the key reservoirs of the resistome, the presence of the mcr-1 gene in human microbiota is alarming. It can be said that the dissemination of colistin resistance genes will be more prevalent in the clinic. Further investigations, such as the surveillance of dissemination of related genes, in countries where colistin resistance has become a serious problem, like Turkey, should be considered. [ABSTRACT FROM AUTHOR]

• We identified mcr-1 gene in fifteen clinical isolates of Enterobacteriaceae. • The mcr-1 -harboring plasmids belonged to different incompatibility group (IncI2, IncX4 and IncP1). • One mcr-1- bearing isolate EC09 was susceptible to colistin with MIC of 0.5 mg/L. • EC09 demonstrated lowest transcription level of mcr-1 gene. Colistin resistance mediated by plasmids for their rapid dissemination in Enterobacteriaceae is alarming. We aimed to characterize the genetic features of mcr-1 gene as well as the role of promoters in gene expression and levels of colistin resistance among clinical isolates of Enterobacteriaceae. Methods: Clinical isolates of Enterobacteriaceae were collected in thirteen cities in China and screened for mcr-1 gene using polymerase chain reaction (PCR) amplification and sequencing. Antimicrobial susceptibility testing, transformation assay and plasmid sequencing, quantitative real-time PCR were performed for mcr -1-positive isolates. Promoter-probe vector pKK232-8 was utilized to assess the activity of the mcr-1 promoters. This study identified the mcr-1 gene in 15 clinical isolates of Enterobacteriaceae, among which 14 were resistant to colistin, with MICs of 4–8 mg/L, while one mcr-1- bearing isolate EC09 was susceptible to colistin, with an MIC of 0.5 mg/L. Moreover, mcr-1 -harbouring plasmids from 10 clinical isolates were transferrable via transformation and belonged to different incompatibility groups (IncI2 and IncX4). Plasmid pEC09 failed to transform and belonged to IncP1. A genetic structure containing the mcr-1-pap2 element was detected in these plasmids. EC09 demonstrated the lowest transcription level of mcr-1 gene, as determined by quantitative real-time PCR, which was in accordance with its susceptibility to colistin. Furthermore, the promoter activity of mcr-1 in pEC09 was the lowest, as determined by promoter-probe vector pKK232-8. Promoter variations were associated with expression of the mcr-1 gene and ultimately the levels of colistin resistance. [ABSTRACT FROM AUTHOR]

To date, the genomic characterization of foodborne bacteria carrying the mobile colistin resistance gene mcr-1 and transferability of mcr-1 -carrying plasmids between wild-type bacteria have not been studied in detail. We retrospectively investigated the prevalence of mcr-1 -positive Salmonella and Escherichia coli isolated from retail food products, food supply chain, and clinical samples across China in the last decade (2006–2017). The horizontal transfer of mcr-1 -bearing plasmids and their complete nucleotide sequence were characterized using conjugation, S1 -nuclease pulsed-field gel electrophoresis, and Southern hybridization, coupled with Illumina and Nanopore sequencing. Twelve (0.67%) mcr-1 -positive strains were identified from 1789 non-duplicated isolates, including 1283 Salmonella and 506 E. coli. Eleven (21.7‰) mcr-1 -positive E. coli strains were identified from the isolates collected during 2006–2017, which was significantly more prevalent than mcr-1 -positive Salmonella in this period (0.78‰, 1/1283; P < 0.05). All donors (nine mcr-1 -positive isolates, designated as D1–9) were multidrug resistant with diverse antimicrobial susceptibility profiles and were resistant to polymyxin B. mcr-1 -carrying plasmids in donors were successfully transferred to recipients at frequencies of 4.6 × 10−2 to 6.25 × 10−4 per recipient cell. A ~33 kb IncX4-type plasmid in D1, which carried mcr-1 with the insertion sequence IS 26 upstream, was effectively transferred to recipient R1. D2, D4, and their corresponding transconjugants harbored a ~60 kb IncI2-type plasmid with the insertion sequence IS Apl1 upstream of mcr-1. A ~60 kb conjugative mcr-1 -bearing plasmid derived from D5 also belonged to type IncI2 and contained the mcr-1 gene cassette IS Ecp1 - bla CTX-M-55 - mcr-1 -PAP2. In conclusion, mcr-1 was commonly detected in type IncI2, IncX4, and IncHI2 plasmids and mcr-1 encoding colistin resistance was successfully transferred between foodborne and clinical strains of E. coli and Salmonella isolated in China. mcr-1 gene cassettes including IS 26 - mcr-1 -PAP2, IS APl1 - mcr-1 -PAP2, and IS Ecp1 - bla CTX-M-55 - mcr-1 -PAP2 can be transferred horizontally between wild-type bacteria via conjugation. The new mcr-1 gene cassette discovered in this study provided evidence for co-transfer of mcr-1 and other antibiotic resistance genes. This finding suggests that antibiotics, other than colistin, should be used in combination for the treatment and prevention of diseases caused by foodborne pathogens. The co-transfer of mcr-1 and other antibiotic resistance genes will also enhance antibiotic resistance in foodborne pathogens. • Prevalence of mcr-1 in foodborne and clinical Salmonella and Escherichia coli was explored. • mcr-1 was detected in IncI2, IncX4, and IncHI2 plasmids in wild-type strains. • mcr-1 gene cassettes can be transferred between wild-type bacteria via conjugation. [ABSTRACT FROM AUTHOR]

Background Efficacy of Colistin the last line agent against infections due to multidrug-resistant (MDR) gram-negative pathogens, has been challenged when Liu et al. reported a plasmid-mediated gene, mcr-1 , in 2015. Thereby this plasmid-borne mcr has been reported in bacterial isolates worldwide taken from humans, animals, farms, foods, and the environment. The present work invesitigate the mcr gene among clinical isolates of Acinetobacter Baumannii at our tertiary referral hospital of India. Methods The study was conducted at Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India. MIC values for 100 consecutive non-duplicate MDR isolates of Acinetobacter were checked for Colistin. PCR amplification of mcr gene was performed followed by sequencing of the amplicons. Clinical features of patients infected with mcr positive isolates were unveiled. Clonal relatedness of these isolates was investigated by Pulsed-field gel electrophoresis (PFGE). The mcr-1 localization was checked by conjugation followed by PFGE southern hybridization. Results 20/100 (20%) isolates were colistin resistant with having MIC Values of more than 8≤ µg/mL. The 20 colistin resistances isolates were PCR positive for mcr-1 and had been assigned EMBL/GeneBank nucleotide accession numbers MH730099-MH730118. Oher antibiotic resistance gene like ESBL, NDM-1, VIM, and 16s rRNA methyl transferases like Arm A, rmtC, rmt F were also found in these isolates. Majority of these patients recovered from the infection (65%) after proper antibiotic therapy.The IS Apl1 transposable elements were not detected in these isolates. These isolates were found clonally unrelated when analyze by pulsed-field gel electrophoresis. The conjugation attempt to transfer mcr-1 to recipient's E. coli J53 failed, Southern hybridization showed that mcr-1 was found located on chromosome in multiple copies. Conclusion This is the first case of mcr-1 in a human clinical isolate in Acinetobacter Baumnnii from India. These findings highlight the vertical transferability of colistin resistance by mcr-1 gene in Acinetobacter Baumnnii with the association of known some unknown insertion sequence located on chromosome. Strategies required to contain their spread and evolution of such genes. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]