Carbapenem-resistant Enterobacteriaceae (CRE) present an urgent threat to public health. While carbapenem antimicrobials are restricted in food-producing animals, other β-lactams, such as ceftiofur, are used in livestock. This use may provide selection pressure favoring the amplification of carbapenem resistance but this relationship has not been established. Previously unreported from US livestock, plasmid-mediated CREs have been reported from livestock in Europe and Asia.
Environmental and fecal samples were collected from a 1,500 sow, US farrow-to-finish operation during 4 visits over a 5 month period, 2015. Samples were screened using selective media for the presence of CRE, with resulting carbapenemase-producing isolates further characterized.
Of 30 environmental samples collected from a nursery room on our initial visit, 2 (7%) samples yielded 3 isolates: 2 ST 218 Escherichia coli and 1 Proteus mirabilis, carrying the metallo-β-lactamase gene blaIMP-27 on IncQ1 plasmids. We recovered 15 IMP-27-bearing isolates of multiple Enterobacteriaceae species from 11 of 24 (46%) environmental samples from 2 farrowing rooms collected on our third visit. These isolates each also carried blaIMP-27 on IncQ1 plasmids. No CRE isolates were recovered from fecal swabs or samples in this study.
As is common in US swine production, piglets on this farm receive ceftiofur at birth, with males receiving a second dose at castration (~day 6). This selection pressure may favor the dissemination of blaIMP-27-bearing Enterobacteriaceae in this farrowing barn. The absence of this selection pressure in the nursery and finisher barns likely resulted in the loss of the ecological niche needed for maintenance of this carbapenem resistance gene.
Dixie F. Mollenkopf, Jason W. Stull, Dimitria A. Mathys, Andrew S. Bowman, Sydnee M. Feicht, Susan V. Grooters, Joshua B. Daniels and Thomas E. Wittum; Carbapenemase-Producing Enterobacteriaceae Recovered from the Environment of a Swine Farrow-to-Finish Operation in the United States; Antimicrob. Agents Chemother.; Posted Online 5 December 2016 doi:10.1128/AAC.01298-16
[Editor’s note: This study provides an opportunity to remind veterinarians of the restrictions on the extra-label use of cephalosporins (including ceftiofur). The use of ceftiofur for prevention of disease is prohibited as is use at unapproved doses, frequencies, durations, or routes of administration; or if the drug is not approved for that species and production class. Although not associated with this study, as a reminder, any extra-label use of fluorquinolones (baytril) is also illegal. Now is a good opportunity to review these restrictions with your clients to ensure they are in compliance with the regulations and that all antimicrobial decisions are based on sound diagnostics and applied in accordance with judicious use guidelines and stewardship principles.]