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Strain diversity of CTX-M-producing Enterobacteriaceae in individual pigs: insights into the dynamics of shedding during the production cycle

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The aim of this study was to evaluate population dynamics of CTX-M-producing Enterobacteriaceae in individual pigs on a farm positive for CTX-M-14-producing Escherichia coli. Fecal samples were collected once around the farrowing time from five sows and four times along the production cycle from two of their respective offspring. Multiple colonies per sample were isolated on cefotaxime-supplemented MacConkey agar with and without prior enrichment, resulting in 98 isolates identified by MALDI-TOF mass spectrometry and tested for blaCTX-M. CTX-M-positive isolates (n=86) were typed by pulsed-field gel electrophoresis (PFGE). Plasmids harboring blaCTX-M were characterized in 22 representative isolates by replicon typing and restriction fragment length polymorphism. Based on PFGE, all individuals shed unrelated CTX-M-14-producing E. coli strains during the course of life. Concomitant shedding of CTX-M-2/97-producing Proteus mirabilis or Providencia rettgeri was observed in two sows and two offspring. At least two genetically unrelated CTX-M-producing E. coli strains were isolated from approximately one fourth of the samples with remarkable differences between isolates obtained by enrichment and direct plating. A clear decrease in strain diversity was observed after weaning. Dissemination of blaCTX-M-14 within the farm was attributed to horizontal transfer of an IncK plasmid that did not carry additional resistance genes and persisted in the absence of antimicrobial selective pressure. Assessment of strain diversity was shown to be influenced by the production stage from which samples were collected as well as by the isolation method, providing useful information for design and interpretation of future epidemiological studies of CTX-M-producing Enterobacteriaceae in pig farms.

OriginalsprogEngelsk
TidsskriftApplied and Environmental Microbiology
Vol/bind80
Udgave nummer21
Sider (fra-til)6620-6626
Antal sider7
ISSN0099-2240
DOI
StatusUdgivet - 2014

ID: 123728235