Objectives To characterize putative AmpC-hyperproducing third-generation cephalosporin-resistant E. coli from dairy farms and their phylogenetic relationships; to identify risk factors for their presence; and to assess evidence for their zoonotic transmission into the local human population. Methods Proteomics was used to explain differences in antimicrobial susceptibility. WGS allowed phylogenetic analysis. Multilevel, multivariable logistic regression modelling was used to identify risk factors. Results Increased use of amoxicillin/clavulanate was associated with an increased risk of finding AmpC hyperproducers on farms. Expansion of cephalosporin resistance in AmpC hyperproducers was seen in farm isolates with marR mutations (conferring cefoperazone resistance) or when AmpC was mutated (conferring fourth-generation cephalosporin and cefoperazone resistance). Phylogenetic analysis confirmed the dominance of ST88 amongst farm AmpC hyperproducers but there was no evidence for acquisition of farm isolates by members of the local human population. Conclusions Clear evidence was found for recent farm-to-farm transmission of AmpC-hyperproducing E. coli and of adaptive mutations to expand resistance. Whilst there was no evidence of isolates entering the local human population, efforts to reduce third-generation cephalosporin resistance on dairy farms must address the high prevalence of AmpC hyperproducers. The finding that amoxicillin/clavulanate use was associated with an increased risk of finding AmpC hyperproducers is important because this is not currently categorized as a highest-priority critically important antimicrobial and so is not currently targeted for specific usage restrictions in the UK.
Cefalexin is a widely used 1 st generation cephalosporin, and resistance in Escherichia coli is caused by Extended-Spectrum (e.g., CTX-M) and AmpC β-lactamase production and therefore frequently coincides with 3 rd generation cephalosporin resistance. However, we have recently identified large numbers of E. coli isolates from human infections, and from cattle, where cefalexin resistance is not β-lactamase mediated. Here we show, by studying laboratory selected mutants, clinical isolates, and isolates from cattle, that OmpF porin disruption or downregulation is a major cause of cefalexin resistance in E. coli . Importantly, we identify multiple regulatory mutations that cause OmpF downregulation. In addition to mutation of ompR , already known to downregulate OmpF and OmpC porin production, we find that rseA mutation, which strongly activates the Sigma E regulon, greatly increasing DegP production, which degrades OmpF, OmpC and OmpA. Furthermore, we reveal that mutations affecting lipopolysaccharide structure, exemplified by the loss of GmhB, essential for lipopolysaccharide heptosylation, also modestly activate DegP production, resulting in OmpF degradation. Remarkably, given the critical importance attached to such systems for normal E. coli physiology, we find evidence for DegP-mediated OmpF downregulation, gmhB and rseA loss of function mutation in E. coli isolates derived from human infections. Finally, we show that these regulatory mutations enhance the ability of group 1 CTX-M β-lactamase to confer reduced carbapenem susceptibility, particularly those mutations that cause OmpC in addition to OmpF downregulation.
18Objectives. To characterise putative AmpC hyper-producing 3 rd generation cephalosporin-19 resistant E. coli from dairy farms and their phylogenetic relationships as well as to identify risk 20 factors for their presence; to assess evidence for their zoonotic transmission into the local 21 human population 22Methods. Proteomics was used to explain differences in antimicrobial susceptibility. Whole 23 genome sequencing allowed phylogenetic analysis. Multilevel, multivariable logistic 24 regression modelling was used to identify risk factors. 25Results. Increased use of amoxicillin-clavulanate was associated with an increased risk of 26finding AmpC hyper-producers on farms. Expansion of cephalosporin resistance in AmpC 27hyper-producers was seen in farm isolates with marR mutations (conferring cefoperazone 28 resistance) or when AmpC was mutated (conferring 4 th generation cephalosporin and 29 cefoperazone resistance). Phylogenetic analysis confirmed the dominance of ST88 amongst 30 farm AmpC hyper-producers but there was no evidence for acquisition of farm isolates by 31 members of the local human population. 32Conclusions. In this two-year surveillance study of 53 dairy farms, AmpC hyper-production 33 was the cause of cefotaxime resistance in 46.2% of E. coli. There was evidence of recent 34 farm-to-farm transmission and of adaptive mutations to expand resistance. Whilst there was 35 no evidence of isolates entering the local human population, efforts to reduce 3 rd generation 36 cephalosporin resistance on dairy farms must address the high prevalence of AmpC hyper-37 producers. The finding that amoxicillin-clavulanate use was associated with increased risk of 38 finding AmpC hyper-producers is important because this is not currently categorised as a 39 highest-priority critically important antimicrobial and so is not currently targeted for specific 40 usage restrictions in the UK. 41 42 43
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.