Carbapenemase-producing Enterobacteriaceae recovered from the environment of a swine farrow-to-finish operation in the United States [PublishAheadOfPrint]

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 bla_IMP-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 bla_IMP-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 bla_IMP-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.

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