title: Quinolone Resistance Mechanisms Among Salmonella enterica in Malaysia.
abstract: The prevalence of quinolone-resistant Salmonella enterica is on the rise worldwide. Salmonella enterica is one of the major foodborne pathogens in Malaysia. Therefore, we aim to investigate the occurrence and mechanisms of quinolone resistance among Salmonella strains isolated in Malaysia. A total of 283 Salmonella strains isolated from food, humans, and animals were studied. The disk diffusion method was used to examine the quinolone susceptibility of the strains, and the minimum inhibitory concentration (MIC) values of nalidixic acid and ciprofloxacin were also determined. DNA sequencing of the quinolone resistance-determining regions (QRDRs) of gyrase and topoisomerase IV genes and the plasmid-borne qnr genes was performed. The transfer of the qnr gene was examined through transconjugation experiment. A total of 101 nalidixic acid-resistant Salmonella strains were identified. In general, all strains were highly resistant to nalidixic acid (average MICNAL, 170 μg/ml). Resistance to ciprofloxacin was observed in 30.7% of the strains (1 ≤ MICCIP ≤ 2 μg/ml). Majority of the strains contained missense mutations in the QRDR of gyrA (69.3%). Silent mutations were frequently detected in gyrB (75.2%), parC (27.7%), and parE (51.5%) within and beyond the QRDRs. Novel mutations were detected in parC and parE. The plasmid-borne qnrS1 variant was found in 36.6% of the strains, and two strains were found to be able to transfer the qnrS1 gene. Overall, mutations in gyrA and the presence of qnrS1 genes might have contributed to the high level of quinolone resistance among the strains. Our study provided a better understanding on the status of quinolone resistance among Salmonella strains circulating in Malaysia.
authors.affiliation: 1 Microbiology Division, Faculty of Science, Institute of Biological Sciences, University of Malaya , Kuala Lumpur, Malaysia .
authors.forename: Kwai Lin
authors.initials: KL
authors.lastname: Thong
authors.affiliation: 1 Microbiology Division, Faculty of Science, Institute of Biological Sciences, University of Malaya , Kuala Lumpur, Malaysia .
authors.forename: Soo Tein
authors.initials: ST
authors.lastname: Ngoi
authors.affiliation: 1 Microbiology Division, Faculty of Science, Institute of Biological Sciences, University of Malaya , Kuala Lumpur, Malaysia .
authors.forename: Lay Ching
authors.initials: LC
authors.lastname: Chai
authors.affiliation: 2 Department of Medical Microbiology, Faculty of Medicine, University of Malaya , Kuala Lumpur, Malaysia .
authors.forename: Cindy Shuan Ju
authors.initials: CS
authors.lastname: Teh
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology; D003227:Conjugation, Genetic; D027081:DNA Gyrase / Q000235:genetics / Q000378:metabolism; D027101:DNA Topoisomerase IV / Q000235:genetics / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008296:Malaysia / Q000453:epidemiology; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism; D015995:Prevalence; D015363:Quinolones / Q000494:pharmacology*; D012480:Salmonella Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D019779:Salmonella enterica / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D015363:Quinolones; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase