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Considering that plasmid conjugation is a major driver for the dissemination of antimicrobial resistance in bacteria, this study aimed to investigate the effects of residual concentrations of antimicrobial growth promoters (AGPs) in poultry litter on the frequencies of IncFII-FIB plasmid conjugation among Escherichia coli organisms. A 2 × 5 factorial trial was performed in vitro, using two types of litter materials (sugarcane bagasse and wood shavings) and five treatments of litter: non-treated (CON), herbal alkaloid sanguinarine (SANG), AGPs monensin (MON), lincomycin (LCM) and virginiamycin (VIR). E. coli H2332 and E. coli J62 were used as donor and recipient strains, respectively. The presence of residues of monensin, lincomycin and virginiamycin increased the frequency of plasmid conjugation among E. coli in both types of litter materials. On the contrary, sanguinarine significantly reduced the frequency of conjugation among E. coli in sugarcane bagasse litter. The conjugation frequencies were significantly higher in wood shavings compared with sugarcane bagasse only in the presence of AGPs. Considering that the presence of AGPs in the litter can increase the conjugation of IncFII-FIB plasmids carrying antimicrobial resistance genes, the real impact of this phenomenon on the dissemination of antimicrobial resistant bacteria in the poultry production chain must be investigated., (© 2022 Society for Applied Microbiology.)

Background: Early in vitro studies suggested that flavophospholipol has plasmid-curing effects and could inhibit conjugation by disrupting pilus formation between bacteria., Objectives: This 36-day controlled-challenge study aimed to evaluate the anti-conjugative and plasmid-curing effect of flavophospholipol in vivo on plasmid-mediated antimicrobial resistance (AMR) in MDR transconjugant Salmonella Enteritidis in chickens., Methods: A total of 270-day-old chicks were randomly assigned to four control and four treatment groups with two doses of in-feed flavophospholipol (10 ppm and 64 ppm) and in the presence and absence of ampicillin in drinking water. Chicks were orally challenged with Salmonella Enteritidis with known plasmid-encoded AMR factors. Cloacal swabs were collected on Day 7, 14 and 23. On Day 35, all chickens were euthanized, and caecal tissue and content were collected. Antimicrobial susceptibility testing was done with a panel of 12 antimicrobials and interpreted according to CLSI breakpoints., Results: Flavophospholipol given in-feed at 64 ppm had an anti-conjugative effect. There was a significant reduction of acquisition of resistance to ampicillin, streptomycin and tetracycline by the recipient strains of Salmonella Enteritidis in treatment groups given flavophospholipol in-feed at 64 ppm ( P <  0.05). This was not seen with flavophospholipol given in-feed at 10 ppm., Conclusions: The results demonstrate that flavophospholipol given in-feed at 64 ppm had an anti-conjugative effect. The results also suggest that AMR is reduced through other mechanisms of action, which are yet to be determined. There is insufficient evidence that flavophospholipol at 64 ppm in feed alone or with sub-therapeutic levels of antibiotics had a plasmid-curing effect., (© The Author(s) 2021. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy.)

Aims: To determine the association between multicellular behaviour, integron status and antibiotic resistance among 87 Ethiopian Salmonella enterica isolates of animal and human origin., Methods and Results: Isolates were characterized for their biofilm forming ability, antimicrobial susceptibility and the presence and characteristics of a class 1 integron and Salmonella genomic island 1 (SGI1). The majority of isolates grown at environmental temperatures (20°C) exhibited robust biofilm formation (72·4%) and displayed RDAR colony morphology on Congo red agar plates. The presence of a class 1 integron correlated with the extent of drug resistance and ability to exhibit multicellular behaviour., Conclusions: Although cellulose production and RDAR morphology correlated with increased multicellular behaviour, neither was required for biofilm formation. Contrary to previous reports, colony morphology was generally consistent within a serovar. No integrons were detected in isolates deficient for multicellular behaviour, indicating a potential role of bacterial community formation in transfer of genetic elements among environmental isolates., Significance and Impact of Study: Infection by Salm. enterica is a major public health problem worldwide. The dominance of multidrug resistance and multicellular behaviour in Salmonella isolates of Ethiopian origin highlights a need for integrated surveillance and further detailed phenotypic and molecular studies of isolates from this region., (© 2014 The Society for Applied Microbiology.)

Objectives: The aim of this study was to elucidate the role of two novel membrane fusion proteins (MFPs) in the susceptibility of Acinetobacter baumannii to antimicrobial agents., Methods: The genome sequence of A. baumannii ATCC 17978 contains two open reading frames (ORFs) annotated as AdeT in the NCBI genome database. Both the putative efflux genes display >30% similarity to known MFPs. The antimicrobial susceptibility profiles of Escherichia coli KAM32 cells carrying the genes were monitored by the broth dilution method. Different efflux pump inhibitors were used for fluorimetric efflux assays. The functions of putative ORFs were confirmed in A. baumannii by insertional inactivation and complementation., Results: E. coli cells carrying the ORFs had decreased susceptibility to antibiotics, disinfectants, dyes and detergents, with enhanced efflux activity. Inactivation of the ORFs and further characterization in A. baumannii confirmed its role in antimicrobial resistance by active efflux., Conclusions: This report describes the functions of novel resistance determinants, members of the MFP family, for the first time in A. baumannii.

Objectives: Acinetobacter baumannii has emerged as an important nosocomial pathogen in hospitalized patients, and causes a multitude of infections with significant morbidity and mortality. The aim of this study was to elucidate the role of a novel efflux pump in A. baumannii., Methods: The open reading frame ABAYE1518, annotated as a putative Methyl Viologen resistance protein in the genome of strain A. baumannii AYE, exhibits >50% similarity with members of the major facilitator superfamily (MFS) multidrug efflux pumps. The antimicrobial susceptibility profiles of Escherichia coli KAM32 cells carrying the putative efflux pump were monitored by broth dilution method. Different efflux pump inhibitors were used for fluorimetric efflux assays. The functions of the putative efflux pump were confirmed in A. baumannii by insertional inactivation and complementation. Its expression in clinical isolates was analysed by reverse transcriptase-PCR., Results: E. coli cells carrying the pump had decreased susceptibility to some antibiotics, disinfectants, dyes and detergents, with enhanced efflux activity. The pump was inactivated in a clinical isolate of A. baumannii AC0037 and further characterization confirmed its role in antimicrobial resistance by active efflux. We found increased expression of the pump in clinical isolates that also exhibited elevated tolerance to antibacterial agents., Conclusions: This report describes the functions of a novel resistance determinant, a member of the MFS efflux pumps, for the first time in A. baumannii.

Objectives: Biocides and dyes are commonly employed in hospital and laboratory settings. We investigated the biocide susceptibilities of a rapidly emerging pathogen, Acinetobacter baumannii, and the underlying molecular mechanisms, with a primary focus on resistance-nodulation-cell division (RND) efflux systems., Methods: Biocide susceptibilities, efflux and in vitro inactivation profiles were monitored in the presence/absence of efflux pump inhibitors. The RND transporters encoded by adeB and adeJ were detected by PCR; null mutants were constructed in the native host. Expression of adeB and adeJ in clinical isolates was assayed by semi-quantitative RT-PCR., Results: Susceptibility testing and phenotypic assays demonstrated the role of active efflux in mediating decreased susceptibility to biocides. Inactivation of either the adeB or adeJ transporter gene led to increased susceptibility to biocides. RT-PCR analysis exhibited increased adeB and adeJ expression in clinical isolates., Conclusions: This is the first study demonstrating the role of efflux pumps in mediating decreased susceptibility to disinfectants and other chemical substrates in A. baumannii.

Objectives: To determine the prevalence and antimicrobial resistance of Campylobacter species in swine reared in the intensive and extensive antimicrobial-free (ABF) production systems at farm and slaughter. In the ABF system, antimicrobials are neither used for growth promotion nor therapeutic purposes., Methods: Swine faecal and carcass swabs were collected from 10 groups of pigs (five each from intensive and extensive ABF farms) at the finishing farm and the slaughter plant. A total of 292 pigs at farm (extensive 118; intensive 174) and 254 carcass swabs (extensive 134; intensive 120) were collected during the study. Campylobacter species were isolated under microaerobic conditions and confirmed by biochemical testing. Up to three presumptive Campylobacter colonies per positive pig/carcass were further characterized. Speciation was done by PCR, targeting ceuE and hipO genes for Campylobacter coli and Campylobacter jejuni, respectively. The isolates were tested for their antimicrobial resistance profile using the agar dilution method against six antimicrobials., Results: A total of 526 Campylobacter isolates were cultured from 292 pigs and 254 carcasses sampled. All the isolates were found to be C. coli. Overall prevalence of C. coli was 55.8% on farm (55% extensive and 56.3% intensive) and 26% at slaughter (32.8% extensive and 18.3% intensive). There was no significant difference in C. coli between the intensive and extensive systems on the finishing farms (P = 0.83). At post-chill stage, C. coli were isolated only from the extensively reared ABF pigs. Antimicrobial resistance against ciprofloxacin (MIC > 4 mg/L) was found at the farm level in both the intensive- and extensive-reared groups. The erythromycin/nalidixic acid/tetracycline resistance pattern (3%) was the most common pattern in multidrug-resistant C. coli., Conclusions: This study highlights the high prevalence of diverse and antimicrobial-resistant C. coli in the ABF production systems of swine. This is the first study reporting the isolation of ciprofloxacin-resistant strains from ABF pigs in the USA and warrants concern.

Objectives: The objectives of this study were to determine antimicrobial resistance and to identify phage types and class 1 integrons among non-typhoidal Salmonella isolates from 24 pig farms in North Carolina collected between 1997 and 2000., Methods: A total of 1314 isolates of 30 serotypes from pig faecal samples were collected and analysed over a 3 year period. The isolates were characterized using antimicrobial susceptibility testing, phage typing, PCR and DNA sequencing for class 1 integrons., Results: A high frequency of resistance to antimicrobial agents including tetracycline (85%), ampicillin (47%), co-amoxiclav (23%) and chloramphenicol (21%) was detected. Two multidrug resistance patterns were common in Typhimurium (including variant Copenhagen): isolates with co-amoxiclav, ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and tetracycline (R-type AxACSSuT) [36%] and isolates with ampicillin, kanamycin, streptomycin, sulfamethoxazole and tetracycline (R-type AKSSuT) [45%] resistance patterns. Definitive Type 104 (DT104) was the most common (34%) among eight phage types identified. AKSSuT was found among non-DT104 phage types, particularly DT21 and DT193. Class 1 integrons were detected among various serotypes including Typhimurium, Derby, Muenchen, Worthington, Bere and Muenster. aadA was the most common resistance gene insert, and the oxa30 beta-lactamase resistance gene was also identified among serovar Muenchen., Conclusions: In this study, two most important multidrug resistance patterns (AxACSSuT and AKSSuT) and phage types of public health significance (DT104 and DT193) constituted two-thirds of the serotype Typhimurium isolates. The findings imply that pigs raised in the commercial production system may pose a risk in serving as reservoirs of resistant Salmonella.