Distribution and genetic characterization of fluoroquinolone resistance gene qnr among Salmonella strains from chicken in China

ABSTRACT

The prevalence and dissemination of the plasmid-mediated fluoroquinolone (FQ) resistance gene qnr in Salmonella are considered serious public health concerns worldwide. So far, no comprehensive large-scale studies have focused on the prevalence and genetic characteristics of the qnr gene in Salmonella isolated from chickens. Herein, this study aimed to investigate the prevalence, antimicrobial resistance (AMR) patterns, and molecular characteristics of chicken-originated qnr-positive Salmonella strains from chicken farms, slaughterhouses, and markets in 12 provinces of China in 2020–2021. The overall prevalence of the qnr gene was 21.13% (56/265), with the highest prevalence in markets (36.11%, 26/72), followed in farms (17.95%, 21/117), and slaughterhouses (10.53%, 9/76). Only the qnrS and qnrB genes were detected, and the prevalence rate of the qnrS gene (19.25%, 51/265) was higher than that of the qnrB gene (1.89%, 5/265). Whole genome sequencing identified 37 distinct AMR genes and 15 plasmid replicons, and the most frequent mutation in quinolone resistance determining regions was parC (T57S; 91.49%, 43/47). Meanwhile, four different qnrS and two qnrB genetic environments were discovered among 47 qnr-positive Salmonella strains. In total, 21.28% (10/47) of the strains were capable of conjugative transfer, and all were qnrS1-positive strains, with the majority of transferable plasmids being IncHI2 types ( n = 4). Overall, the prevalence of qnr-positive Salmonella strains from chickens in China and their carriage of multiple resistance and virulence genes and transferable plasmids is a major concern, which calls for continuous surveillance of qnr-positive Salmonella and the development of measures to control its prevalence and transmission.

IMPORTANCE

Salmonella is a common foodborne pathogen responsible for 155,000 deaths annually worldwide. Fluoroquinolones (FQs) are used as first-line drugs for the treatment of Salmonella infections in several countries and regions. However, the emergence and increasing prevalence of the FQ-resistant gene qnr in Salmonella isolated from chickens have been widely reported. Gaining insight into the genetic mechanisms of AMR genes in chicken could lead to the development of preventive measures to control and reduce the risk of drug resistance. In this study, we identified qnr-positive Salmonellae isolated from chickens in different regions of China and their AMR patterns and genome-wide characteristics, providing a theoretical basis for further control of their prevalence and transmission.