title: Increasing incidence of quinolone resistance in human non-typhoid Salmonella enterica isolates in Korea and mechanisms involved in quinolone resistance.
abstract: OBJECTIVE
  We investigated the trends of nalidixic acid resistance in human non-typhoid Salmonella enterica in a Korean population, and examined some possible mechanisms involved in this resistance.
  
  
  METHODS
  A total of 261 clinical strains were tested. For all strains, the MICs of nalidixic acid were determined. Nalidixic acid-resistant strains underwent further analysis, including determination of MICs of other antibiotics, mutation analysis within the topoisomerase genes, organic solvent tolerance test, western blotting for AcrA, marOR mutation analysis, ciprofloxacin accumulation test, and PCR for the qnr gene. The clonal relationships of Salmonella strains were examined by random amplified polymorphic DNA analysis.
  
  
  RESULTS
  The incidence of nalidixic acid resistance increased from 1.8% in 1995-96 to 21.8% in 2000-02. The resistance rate was higher in S. enterica serotype Enteritidis (21.6%) than in serotype Typhimurium (12.1%). The nalidixic acid resistance rates in Salmonella Enteritidis varied according to the phage type (PT) and Salmonella Enteritidis PT 1 was most commonly associated with resistance to nalidixic acid. Several cases of clonal spread, especially by Salmonella Enteritidis PT 1, were identified. Of the 46 nalidixic acid-resistant strains, 43 had single mutations in the gyrA gene. Four strains were organic solvent-tolerant and were associated with decreased ciprofloxacin accumulation; three of these showed increased expression of AcrA and had novel mutations in marOR (84L). The qnr gene was not identified.
  
  
  CONCLUSIONS
  Recently, the rate of nalidixic acid resistance in Korean clinical Salmonella strains markedly increased and it was partly due to the clonal spread of Salmonella Enteritidis, especially PT 1. The main mechanism of nalidixic acid resistance was a mutation in the gyrA region.
authors.affiliation: Division of Infectious Diseases, Asan Medical Center, University of Ulsan College of Medicine, Songpa-gu, Seoul, Republic of Korea.
authors.forename: Sang-Ho
authors.initials: SH
authors.lastname: Choi
authors.forename: Jun Hee
authors.initials: JH
authors.lastname: Woo
authors.forename: Jung Eun
authors.initials: JE
authors.lastname: Lee
authors.forename: Su Jin
authors.initials: SJ
authors.lastname: Park
authors.forename: Eun Ju
authors.initials: EJ
authors.lastname: Choo
authors.forename: Yee Gyung
authors.initials: YG
authors.lastname: Kwak
authors.forename: Mi-Na
authors.initials: MN
authors.lastname: Kim
authors.forename: Myung-Sik
authors.initials: MS
authors.lastname: Choi
authors.forename: Nam Yong
authors.initials: NY
authors.lastname: Lee
authors.forename: Bok Kwon
authors.initials: BK
authors.lastname: Lee
authors.forename: Nam Joong
authors.initials: NJ
authors.lastname: Kim
authors.forename: Jin-Yong
authors.initials: JY
authors.lastname: Jeong
authors.forename: Jiso
authors.initials: J
authors.lastname: Ryu
authors.forename: Yang Soo
authors.initials: YS
authors.lastname: Kim
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D001434:Bacteriophage Typing; D002939:Ciprofloxacin / Q000378:metabolism; D016172:DNA Fingerprinting; D026942:DNA Topoisomerases / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005798:Genes, Bacterial; D006801:Humans; D007723:Korea; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology*; D009930:Organic Chemicals / Q000494:pharmacology; D019105:Random Amplified Polymorphic DNA Technique; D012480:Salmonella Infections / Q000382:microbiology*; D019779:Salmonella enterica / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D012703:Serotyping; D012997:Solvents / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D009930:Organic Chemicals; D012997:Solvents; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D026942:DNA Topoisomerases