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CRE from US swine farm poses threat of foodborne transmission
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Researchers detected carbapenem-resistant Enterobacteriaceae, or CRE, at a farrow-to-finish operation in the United States, according to a recently published study.
While CRE have been reported in livestock from Europe and Asia, this is the first instance in which they have been identified among U.S. livestock, raising concerns about the possibility of foodborne transmission to the consumer population.
“While they are considered ‘last line of defense’ drugs in human medicine, carbapenem antimicrobials are approved for use in food animal veterinary medicine. However, other [beta-lactams] are commonly used in almost all food animal species worldwide, including ceftiofur and cefquinome extended-spectrum cephalosporin drugs,” Thomas E. Wittum, PhD, professor and chair of veterinary preventive medicine at The Ohio State University, and colleagues wrote in Antimicrobial Agents and Chemotherapy.
“If CRE are present in food animal populations, a large number of consumers may be exposed through the food chain, resulting in a critically important emerging food safety issue.”
The researchers collected fecal samples, fecal swabs, electrostatic clothes and sterile gauze from one 1,500-sow operation during four visits in July, August, October and November 2015. As per barn protocol, piglets routinely received prophylactic Excede (ceftiofur, Zoetis) treatment at first day of life, male pigs received prophylactic ceftiofur at castration (aged 5 to 7 days) and sows received therapeutic Excenel (ceftiofur, Zoetis) if affected by metritis and other bacterial infections.
To detect carbapenem-resistant isolates in both environmental and fecal matter, the researchers incubated samples in combination with agar and biochemical assays overnight in a laboratory setting after each visit to the farm.
Laboratory analysis showed that of 30 environmental samples collected in the first visit, two (7%) samples produced three carbapenem isolates comprising Escherichia coli (n = 2) and Proteus mirabilis (n = 1), which both carried the metallo-beta-lactamase gene blaIMP-27 on IncQ1 plasmids. Further, the researchers recovered 15 blaIMP-27-bearing isolates of several Enterobacteriaceae species from 11 of 24 (46%) environmental samples collected from farrowing rooms at the third visit that also carried blaIMP-27 on IncQ1 plasmids. No such isolates were found in “harvest-ready pigs” in the finisher barn, making it unlikely that resistant enteric pathogens were passed into the food supply. The researchers said there were no CRE isolates recovered from fecal swabs or samples in the study.
They hypothesized that because the piglets received ceftiofur at birth and male piglets received a second dose at castration approximately 6 days later — a common practice in U.S. swine production — this may have selected for resistance to carbapenems in the farrowing rooms. However, because ceftiofur was not used in the nursery and finisher barns, there was no antimicrobial selection pressure on the enteric flora of the animals, resulting in the loss of an ecological niche necessary to maintain the resistance gene.
“The implication of our finding is that there is a real risk that CRE may disseminate in food animal populations and eventually contaminate fresh retail meat products,” Wittum and colleagues wrote. “Foodborne transmission may then produce a reservoir of mobile carbapenemase genes in the enteric flora of consumers.” – by Kate Sherrer
- Reference:
- Mollenkopf DF, et al. Antimicrob Agents Chemother. 2016;doi:10.1128/AAC.01298-16.
Disclosure: The researchers report no relevant financial disclosures.