Emergence of β-Lactamases and Extended-Spectrum β-Lactamases (ESBLs) Producing Salmonella in Retail Raw Chicken in China

beta-Lactamases and extended-spectrum beta-lactamases (ESBLs) producing pathogenic bacteria were widely studied previously in China, but were seldom focused on foodborne Salmonella. In this study, an investigation concerning beta-lactamases and ESBLs producing Salmonella recovered from retail raw chickens was performed. Sixty of 699 foodborne Salmonella isolates were detected as beta-lactamases and ESBLs-producing ones that covered 12 Salmonella serotypes and exhibited different pulsed-field gel electrophoresis genotypes. Forty-four of 60 beta-lactamases and ESBLs-producing strains were simultaneously resistant to ampicillin, amoxicillin/clavulanic acid, ceftiofur, ceftriaxone, and cefoxitin. The most commonly detected beta-lactamases and ESBLs-encoding gene was bla(TEM-1) (n=44), followed by bla(OXA-1) (n=38), bla(CMY-2) (n=29), bla(PSE-1-like) (n=1), bla(CTX-M-3) (n=16), and bla(CTX-M-15) (n=1), respectively. Fourteen, 24, 21, and 1 isolates were detected simultaneously positive for 1, 2, 3, and 4 of the detected beta-lactamases and ESBLs-encoding genes, respectively. A Salmonella strain simultaneously co-carrying bla(TEM-1), bla(OXA-1), bla(CMY-2), and bla(CTX-M-3) was first reported in the present study. Amino acid substitution of Trp244Cys/His247Leu was detected in PSE-1, Val218Asp in CMY-2, and Asp242Gly in CTX-M-15 enzymes, respectively. A difference was found among the amino acid sequences of the detected OXA-1, CMY-2, CTX-M, PSE-1, and TEM-1. The results demonstrated that beta-lactamases and ESBLs were emerging and prevalent in foodborne Salmonella.