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Molecular epidemiology and antibiotic resistance phenotypes and genotypes of salmonellae from food supply chains in China

Chao, Guoxiang, Wang, Chao, Wu, Tianqi, Zhang, Xiaorong, Chen, Jianhao, Qi, Xiaoxing, Cao, Yongzhong, Wu, Yantao, Jiao, Xinan
Food control 2017 v.77 pp. 32-40
Salmonella, ampicillin, animal production, antibiotic resistance, beta-lactamase, cefoperazone, ceftriaxone, chickens, ciprofloxacin, clones, food animals, food supply chain, genetic resistance, genotype, humans, molecular epidemiology, multigene family, multilocus sequence typing, multiple drug resistance, phenotype, serotypes, swine, China, Indiana
Salmonella is an important zoonotic agent and a vehicle for antibiotic resistance genes. Here, 294 isolates from humans and food-producing animals were subjected to serotyping, multilocus sequence typing, and assessment of phenotypic (15 antibiotics) and genotypic (32 resistance genes) antimicrobial resistance. Twenty-two serotypes and 35 sequence types (STs) were identified, the most common STs being ST11, including S. Enteritidis from chickens and humans; ST17, including S. Indiana from chickens; and ST40, including S. Derby from pigs and humans. Antimicrobial resistance phenotypes and genotypes exhibited ST- and serovar-specific features. ST11, clonal complex (CC) 19, ST40, and ST155 were moderately multidrug-resistant (MDR) clones, most of the isolates of which were resistant to between 3 and 6 antibiotics. Isolates of a super-MDR clone, ST17, demonstrated resistance against 9 to 14 antimicrobials, in particular, ampicillin, amoxicillin-clavulanic acid, cefotaxime, cefepime, cefoperazone, ceftriaxone, and ciprofloxacin. Consistent with this, ST17 (S. Indiana) was associated with a gene cluster comprising blaCTX-M (and/or blaOXA-1-like together with blaTEM-1-like), sul1, aacC4, aac(6)-1b, floR, and dfrA17, while the moderately-MDR clones (ST11, S. Enteritidis) were more closely linked to the blaTEM-1-like gene. The similar genetic clones isolated from animals and humans indicate a common ancestor, and implicate animals as a major salmonellae source. Antibiotic abuse in animal production appears to be the origin of MDR and super-MDR isolates, the latter being closely associated with the β-lactamase genes blaCTX-M, blaOXA-1-like, and blaTEM-1-like. Carried by chickens, ST17 (S. Indiana) is an emerging super-MDR clone whose associated resistance genes are expanding to other ST clones and serotypes being transmitted to animals and humans.