Distribution and Antimicrobial Resistance of Salmonella Isolated from Pigs with Diarrhea in China

Abstract

<i>Salmonella</i> can cause enteric diseases in humans and a wide range of animals, and even outbreaks of foodborne illness. The aim of this study was to investigate the frequency and distribution of serovars, and antimicrobial resistance in <i>Salmonella</i> isolates from pigs with diarrhea in 26 provinces in China from 2014 to 2016. A total of 104 <i>Salmonella</i> isolates were identified and the dominant serovar was <i>S.</i> 4,[5],12:i:- (53.9%). All <i>Salmonella</i> isolates were resistant to trimethoprim-sulfamethoxazole, and many were resistant to ampicillin (80.8%) and tetracycline (76.9%). Among 104 <i>Salmonella</i> isolates, <i>aac(6')-Ib-cr</i> was the dominant plasmid-mediated quinolone resistance gene (80.8%), followed by <i>qnrS</i> (47.1%). The pulsed-field gel electrophoresis results suggest that the <i>Salmonella</i> isolates from different regions were genetically diverse, and ST34 was the most prevalent. <i>S.</i> 4,[5],12:i:- isolates is the widespread presence of heavy metal tolerance genes. The fact that the same sequence types were found in different regions and the high similarity coefficient of <i>S.</i> 4,[5],12:i:- isolates from different regions indicate the clonal expansion of the isolates, and the isolates carried various antimicrobial resistance genes. The multidrug resistant <i>Salmonella</i> can be widely detected in pigs, which will present a challenge for farm husbandry.