title: 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.
authors.affiliation: Food Safety and Technology Research Center, Hong Kong PolyU Shenzhen Research Institute, Shenzhen, P. R. China.|State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Dachuan
authors.initials: D
authors.lastname: Lin
authors.affiliation: Food Safety and Technology Research Center, Hong Kong PolyU Shenzhen Research Institute, Shenzhen, P. R. China.|State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Kaichao
authors.initials: K
authors.lastname: Chen
authors.affiliation: Food Safety and Technology Research Center, Hong Kong PolyU Shenzhen Research Institute, Shenzhen, P. R. China.|State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Edward
authors.initials: E
authors.lastname: Wai-Chi Chan
authors.affiliation: Food Safety and Technology Research Center, Hong Kong PolyU Shenzhen Research Institute, Shenzhen, P. R. China.|State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Sheng
authors.initials: S
authors.lastname: Chen
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002645:Chickens; D002939:Ciprofloxacin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D005516:Food Microbiology; D005798:Genes, Bacterial; D006801:Humans; D008460:Meat / Q000382:microbiology*; D009154:Mutation; D010957:Plasmids / Q000235:genetics*; D015995:Prevalence; D012475:Salmonella / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D012480:Salmonella Infections / Q000188:drug therapy / Q000382:microbiology; D034421:Sus scrofa
chemical_list: D000900:Anti-Bacterial Agents; D002939:Ciprofloxacin