Abstract
A total of 154 non-duplicate Salmonella isolates were recovered from 1,105 rectal swabs collected from three large-scale chicken farms (78/325, 24.0%), three large-scale duck farms (56/600, 9.3%) and three large-scale pig farms (20/180, 11.1%) between April and July 2016. Seven serotypes were identified among the 154 isolates, with the most common serotype in chickens and ducks being Salmonella enteritidis and in pigs Salmonella typhimurium. Antimicrobial susceptibility testing revealed that high antimicrobial resistance rates were observed for tetracycline (72.0%) and ampicillin (69.4%) in all sources. Class 1 integrons were detected in 16.9% (26/154) of these isolates and contained gene cassettes aadA2, aadA1, drfA1-aadA1, drfA12-aadA2, and drfA17-aadA5. Three β-lactamase genes were detected among the 154 isolates, and most of the isolates carried blaTEM−1(55/154), followed by blaPSE−1(14/154) and blaCTX−M−55 (11/154). Three plasmid-mediated quinolone resistance genes were detected among the 154 isolates, and most of the isolates carried qnrA (113/154), followed by qnrB (99/154) and qnrS (10/154). Fifty-four isolates carried floR among the 154 isolates. Multilocus sequence typing (MLST) analysis showed that nine sequence types (STs) were identified; ST11 was the most frequent genotype in chickens and ducks, and ST19 was identified in pigs. Our findings indicated that Salmonella was widespread, and the overuse of antibiotics in animals should be reduced considerably in developing countries.
Highlights
Salmonella is an important source of foodborne diseases that cause morbidity and mortality worldwide
The prevalence (9.3%) in ducks was similar to that obtained from duck farms in Sichuan province (12.0%) (Li et al, 2013) but was lower than those reported in Penang, Malaysia (39.0%) (Adzitey et al, 2012), and in South Korea (65.2%) (Cha et al, 2013)
The dominant serotype in pigs was Salmonella typhimurium, which was the most common serovar isolated from humans and it can lead to severe human and animal diseases (Deng et al, 2012), but it was different from other studies, where the dominant serotype in pig farms was Salmonella IIIb in Henan province (Kuang et al, 2015), and Salmonella derby in England and Wales (Miller et al, 2011)
Summary
Salmonella is an important source of foodborne diseases that cause morbidity and mortality worldwide. Among 94 million cases of non-typhoid Salmonella infections, it was presumed that approximately 85% of the cases were induced by food origin Salmonella (Chiu et al, 2010). In China, Salmonella causes an estimated 22.2% of foodborne diseases (Wang et al, 2007). More than 2,600 serovars are classified based on the reactivity of antisera to O and H antigens (Stevens et al, 2009), and the serovars from farms have a significant overlap with those causing illnesses in humans (Alcaine et al, 2006). Animals have been recognized as an important reservoir for Salmonella, and this pathogen can be transferred to humans via the food chain, posing a serious threat to human health (Vo et al, 2006)
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