Increasing prevalence of ciprofloxacin-resistant food-borne Salmonella strains harboring multiple PMQR elements but not target gene mutations

Abstract

Fluoroquinolone resistance in Salmonella has become increasingly prevalent in recent years. To probe the molecular basis of this phenomenon, the genetic and phenotypic features of fluoroquinolone resistant Salmonella strains isolated from food samples were characterized. Among the 82 Salmonella strains tested, resistance rate of the three front line antibiotics of ceftriaxone, ciprofloxacin and azithromycin was 10%, 39% and 25% respectively, which is significantly higher than that reported in other countries. Ciprofloxacin resistant strains typically exhibited cross-resistance to multiple antibiotics including ceftriaxone, primarily due to the presence of multiple PMQR genes and the blaCTX-M-65, blaCTX-M-55 blaCMY-2 and blaCMY-72 elements. The prevalence rate of the oqxAB and aac(6’)-Ib-cr genes were 91% and 75% respectively, followed by qnrS (66%), qnrB (16%) and qnrD (3%). The most common PMQR combination observable was aac(6’)-Ib-cr-oqxAB-qnrS2, which accounted for 50% of the ciprofloxacin resistant strains. Interestingly, such isolates contained either no target mutations or only a single gyrA mutation. Conjugation and hybridization experiments suggested that most PMQR genes were located either in the chromosome or a non-transferrable plasmid. To summarize, findings in this work suggested that PMQRs greatly facilitate development of fluoroquinolone resistance in Salmonella by abolishing the requirement of target gene mutations.

Phenotypic and genotypic profile of clinical and animal multidrug-resistantSalmonella entericaisolates from Mexico

“…), our finding of an in vitro susceptibility above 90% for these antibiotics (except NAL) indicates still an acceptable effectiveness, however, is very likely that the percentage of AMR could increase steadily due to mobile genetic elements like plasmids, transposons or integrons and subsequently their dissemination through animal‐origin food, this scenario is observed in other countries, especially from Asia, where S. enterica isolates from pork and chicken meat have a higher resistant rate for all the antibiotic tested in comparison with our work (up to 39% for CIP, 10% for CTX and 40% for GEN) (Lin et al . ).…”

Genetic markers associated with resistance to beta-lactam and quinolone antimicrobials in non-typhoidal Salmonella isolates from humans and animals in central Ethiopia

“…We have also not detected PMQR genes in any of the isolates. Other resistance mechanisms not tested in this study such as multidrug efflux pumps, other PMQR mechanisms recently described in Salmonella such as oqxAB efflux pump [19], and altered outer membrane porins might be involved [14]. …”

“…These resistance determinants have been observed in various gram negative organisms including Salmonella [16, 17]. In recent years, the rate of resistance to ciprofloxacin has increased considerably in both clinical and food isolates of Salmonella [6, 18, 19]. …”

Antimicrobial Resistance of Salmonella enterica Serovar Typhimurium in Shanghai, China

“…Mutations at different sites contribute to different levels of resistance to ciprofloxacin, and simultaneous mutations in both gyrA and parC genes produce high levels of ciprofloxacin resistance. Besides, most isolates with decreased susceptibility to ciprofloxacin contain a mutation in gyrA or PMQR genes (Ling et al, 2003; Lin et al, 2015). In the present study, we found that six isolates had double mutations (S83F/D87N or D87G) in the gyrA gene and a single mutation (S80R) in the parC gene.…”