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Plasmid mediated antimicrobial resistance. Characterizing extended-spectrum lactamases in E.coli isolated from cattle

Abstract number: P1619

Boinett C.J., Coldham N., Anjum M.F., Kirchner M., Carattoli A., Woodward M.J.

Objectives: The aim of this study was to characterize plasmids harbouring CTX-M genes and other antimicrobial resistance markers, with respect to their relative plasticity and ease of dissemination.

Methods: Bovine Escherichia coli isolates (n = 52) found to posses the CTX-M gene, which encodes for a b-lactamase conferring resistance to extended spectrum b-lactams were examined. Resistance phenotypes were determined using the disk diffusion assay. Isolates were also subjected to analysis by pulse field gel electrophoresis, plasmid profiling, miniaturized DNA microarray analysis and PCR based replicon typing.

Results: All 52 isolates were found to be resistant to cefotaxime (CTX), however when analysed by PFGE, their macro-restriction profiles varied considerably with similarities between 25–100%. Analysis of the plasmid content showed that all 52 isolates harboured multiple large plasmids (50–100kb). DNA microarray analysis was used to identify genes that confer antimicrobial resistance. All the isolates were found to encode either CTX-M group 1 (CTX-M-1, -15 and -32) or CTX-M group 9 (CTX-M-14 and -14b) variants, with 3 isolates encoding both CTX-M-14 and -15 genes and the majority encoding multiple antimicrobial resistance genes. Plasmid transfer rates were determined for 26 / 52 strains by in vitro conjugation studies. The isolates for conjugation were selected on the basis of distinct plasmid profiles and also considering their antimicrobial resistance profiles. Twelve of these isolates were able to transfer plasmids conferring cefotaxime resistance to recipient E. coli K12 strains with frequency of transfer rates between 3.75×10-3 and 3.69×10-7. The majority of the isolates harboured multi-replicon plasmids, with 39 / 52 having an IncF variant.

Conclusion: These data confirm the highly variable nature of the CTX-M ESBL E. coli strains found on different farms although these were found to carry only limited CTX-M types. Interestingly 20 isolates encoded the CTX-M-15 gene, the most prevalent b-lactamase worldwide. FIA, FIB, FII replicons in E. coli have been linked with the dissemination of CTX-M-15 genes and therefore the success of plasmids harbouring this gene. It is proposed that complex methods of gene acquisition may have given rise to these CTX-M encoding strains and that the plasmids are likely to be promiscuous.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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