Detection of Extended-Spectrum Beta-Lactamase-Producing and Carbapenem-Resistant Bacteria from Mink Feces and Feed in the United States

Antibiotic-resistant infections caused by extended-spectrum beta-lactamases (ESBLs) and carbapenemases are increasing worldwide. Bacteria resistant to extended-spectrum cephalosporins and last resort carbapenems have been reported from food animals and their environments. Other concentrated nonfood-producing animals such as mink farming can be a reservoir of bacteria resistant to these critically important antibiotics. The objective of this study was to determine the prevalence of ESBL-producing bacteria and carbapenem-resistant (CR) bacteria from mink fecal (n = 42) and feed (n = 8) samples obtained from a commercial mink farm in the United States. The most prevalent ESBL-producing bacteria identified from the fecal samples were Escherichia coli (93%), Klebsiella pneumoniae (76%), and Proteus species (88%). E. coli (100%) and K. pneumoniae (75%) were also the most prevalent ESBL-producing bacteria identified from feed samples. All ESBL E. coli isolates were resistant to penicillin and most cephem beta-lactam antibiotics. Among the ESBL E. coli isolates, co-resistance was observed to ciprofloxacin (33%) and gentamicin (28%) indicating multidrug resistance. ESBL E. coli isolates predominantly carried bla(CTX-M-14) and bla(CTX-M-15) genes. Although all feed K. pneumoniae isolates carried bla(CTX-M-9), all fecal K. pneumoniae isolates carried bla(SHV). CR Pseudomonas species (7%), Hafnia alvei (24%), and Myroides odoratimimus (9.5%) were detected from fecal samples. H. alvei (37.5%) was the only CR bacteria detected from the feed samples. All CR isolates were polymerase chain reaction negative for the tested carbapenemases that are commonly reported, which may indicate intrinsic rather than acquired resistance. This study indicates that mink production can be a reservoir for bacteria resistant to the highest priority critically important antibiotics for human health.