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ARS Home » Research » Publications at this Location » Publication #336600
Title: Plasmid mediated colistin resistance in food animal intestinal contents detected by selective enrichment

Author
item Cook, Kimberly - Kim
item Meinersmann, Richard - Rick
item LADELY, SCOTT - Former ARS Employee
item Plumblee Lawrence, Jodie
item WHITAKER, RACHEL - Food Safety Inspection Service (FSIS)
item WILLIAMS, KAY - Food Safety Inspection Service (FSIS)
item DESSAI, UDAY - Food Safety Inspection Service (FSIS)
item Thacker, Eileen

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 1/12/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Colistin is classified as an antibiotic that is critically important for human medicine in treatment of multi-drug resistant infections. Recently a plasmid-mediated colistin resistance gene (mcr-1) was discovered in China followed by global reports of mcr-1 genes in bacterial isolates from humans and livestock sources. The presence of colistin resistance on a plasmid greatly increases the likelihood that it will be transferred among bacteria; increasing the incidence of resistance and potentially limiting the lifespan of this critically important antibiotic. Therefore, the objective of this study was to determine the prevalence of plasmid-mediated colistin resistance in species of the family Enterobacteriaceae associated with U.S. food animal production. Cecal (intestinal) samples from over 2,000 swine, turkey, chicken and beef cattle were selectively enriched in buffered peptone water with colistin (2 ug/ml) in overnight incubations and plated onto MacConkey’s agar with colistin. Isolates were screened by PCR targeting the mcr-1 gene. Two E. coli isolates from swine intestinal contents were positive for the mcr-1 gene making the overall prevalence of plasmid mediated colistin resistance 0.1% for food animals at slaughter. One isolate was resistant to four other drugs (ampicillin, streptomycin, sulfisoxazole, and tetracycline) and the second isolate was only resistant to colistin. The isolates that did carry the gene were not strains commonly associated with those known to cause human disease. This study demonstrated that plasmid-mediated colistin resistance is rare in animals at slaughter and suggests that there is limited potential for widespread dissemination of the gene via food animal production.

Technical Abstract: Colistin (polymyxin E) is a cationic polypeptide antibiotic that has broad-spectrum activity against Gram-negative bacteria. It is classified as critically important in human medicine for treating hard-to-treat multi-drug resistant infections. Recently a plasmid-mediated colistin resistance gene (mcr-1) was discovered in China followed by global reports of mcr-1 genes in bacterial isolates from humans and livestock sources, however information on prevalence of mcr-1 in the U.S. was lacking. The presence of colistin resistance on a plasmid greatly increases the likelihood that mcr-1will be horizontally transferred among a broad spectrum of bacteria including pathogens. Such dissemination of mcr-1can potentially limit the lifespan of this critically important antibiotic. Therefore, the objective of this study was to determine the prevalence of plasmid-mediated colistin resistance in members of Enterobacteriaceae associated with U.S. food animal production. Cecal (intestinal content) samples from over 2,000 swine, turkey, chicken and beef cattle were selectively enriched in buffered peptone water with colistin (2 ug/mL) in overnight incubations and plated onto MacConkey’s agar with colistin (2 ug/mL). Isolates were screened by PCR for the presence of the mcr-1 gene. Two E. coli isolates from two samples of swine intestinal contents were positive for the mcr-1 gene putting the overall prevalence of plasmid mediated colistin resistance in food animals at slaughter in the U.S. at 0.1%. One E. coli isolate was resistant to four other drugs (ampicillin, streptomycin, sulfisoxazole, and tetracycline) and the second isolate was only resistant to colistin. Both the strains of E. coli with the mcr-1gene are not commonly associated with human disease. This study demonstrated that plasmid-mediated colistin resistance is rare in animals at slaughter in the U.S. and suggests that the potential for widespread dissemination of the mcr-1gene in the country via food animal production may be limited.