Occurrence of ciprofloxacin resistance, plasmid-mediated quinolone resistance genes and virulence factors in Salmonella enterica serovar Enteritidis isolated from broilers in Thailand isolated from broilers in Thailand

Salmonella Enteritidis is one of the most common serovars associated with gastroenteritis in humans. Fluoroquinolone resistance in non-typhoidal Salmonella including S. Enteritidis has increased globally and is considered as a threat to public health. In this study, we aimed to investigate the occurrence of ciprofloxacin resistance and plasmid-mediated quinolone resistance (PMQR) genes, and examine virulence gene profiles of 69 S. Enteritidis isolates recovered from 46 boot swab and 23 intestinal samples collected from 69 commercial intensive broiler farms in Thailand. Ciprofloxacin susceptibility of these isolates was determined using microbroth dilution method. PCR was used to detect 5 common PMQR genes (qnrA, qnrB, qnrS, aac(6')-Ib-cr and qepA) and 12 important virulence genes (agfA, invA, spaN, prgH, sitC, ssaQ, mgtC, sopB, sifA, tolC, cdtB and spvC). All S. Enteritidis showed reduced susceptibility to ciprofloxacin, with the MIC values of 0.125-0.50 µg/mL. However, these isolates did not carry PMQR genes investigated. The same virulence profile was observed among 69 S. Enteritidis isolates in which 11 virulence genes, except cdtB, were detected. The presence of virulence genes identified in invasive salmonellosis in the S. Enteritidis isolates with reduced susceptibility to ciprofloxacin could be of public health concerns. Our findings underline the need for constant monitoring of ciprofloxacin-resistant S. Enteritidis in poultry production chain to reduce public health risk.