Characterization of integrons and antimicrobial resistance in Salmonella from broilers in Shandong, China

Abstract Salmonella spp. are one of the most important foodborne bacterial pathogens in human beings and animals. This study aimed to analyze the prevalence and characterization of Salmonella from broilers in Shandong, China. A total of 67 Salmonella were recovered from 600 rectal swabs collected from three large-scale intensive broiler farms (67/600, 11.2％) between May to October 2018. Among Salmonella isolates, the most common serovars were S. Enteritidis and S. Typhimurium. The highest occurrence of resistance observed was for PB (100％), and followed by AMP (68.7％). The multi-drug resistant (MDR) Salmonella isolation rate was observed to be 53.7％. Four β-lactamase genes were detected among the isolates, all the isolates carried blaTEM (67/67, 100％), followed by blaOXA (19/67, 28.4％), blaCTX-M (17/67, 25.4％), and blaPSE (7/67, 10.4％); four plasmid-mediated quinolone resistance gene were detected among the isolates, the prevalent resistance genes was aac(6’)-Ib-cr (18/67, 26.9％), followed by oqxB (9/67, 13.4％), qnrB (6/67, 9.0％), and qnrD (1/67, 1.5％); the prevalent rate of mcr-1 was 6.0％(4/67). Class 1 integrons were detected in 26.9％ of these isolates and contained seven groups of resistance gene cassettes. MLST analysis revealed seven sequence types, and ST11 was the most frequent sequence types. This study indicated that reduction of Salmonella and strict control on the use of antibiotics in more than 5000 million broilers in Shandong are the vitally important measure to keep public health.