title: Analysis of the mechanisms of quinolone resistance in clinical isolates of Citrobacter freundii.
abstract: The presence of gyrA, gyrB and/or parC mutations, quinolone uptake, outer membrane protein profiles and epidemiological relationship were studied in 12 clinical isolates of Citrobacter freundii. No alterations were observed in the gyrB gene of any of the strains, or gyrA or parC of the four quinolone-susceptible strains (nalidixic acid MIC of 2-4 mg/L, and a ciprofloxacin MIC of 0.006-0.06 mg/L). The quinolone-resistant strains were classified into two groups: one group (group A) composed of strains resistant to nalidixic acid but not to ciprofloxacin and another (group B) including those resistant to both antibiotics with a mutation at codon 83 of the gyrA gene (Thr-->Ile), but no alteration in either parC or gyrB genes. In group B, three of the four resistant isolates, with a nalidixic acid MIC > 1024 mg/L and ciprofloxacin MIC of 8-32 mg/L, showed concomitant mutations at codons 83 and 87 of the gyrA gene (Thr-->Ile and Asp-->Tyr, respectively) as well as a single mutation in codon 80 of the parC gene (Ser-->Ile). The fourth isolate did not possess the mutation at codon 87 of gyrA. Two strains belong to the same clone and, although they had the same type of mutations in the gyrA and parC genes, showed different MICs of ciprofloxacin. This difference was related to an efflux pump mechanism. Mutations in the gyrA and parC genes play the main role in quinolone resistance development in Citrobacter freundii, although other factors such as overexpression of efflux pumps can play a complementary role and thus modulate the final quinolone MIC.
authors.affiliation: Departament de Microbiologia, IDIBAPS, Hospital Clínic, Facultat de Medicina, Universitat de Barcelona, Villarroel 170, 08036-Barcelona, Spain.
authors.forename: M M
authors.initials: MM
authors.lastname: Navia
authors.forename: J
authors.initials: J
authors.lastname: Ruiz
authors.forename: A
authors.initials: A
authors.lastname: Ribera
authors.forename: M T
authors.initials: MT
authors.lastname: de Anta
authors.forename: J
authors.initials: J
authors.lastname: Vila
mesh_terms: D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry; D002939:Ciprofloxacin / Q000378:metabolism / Q000494:pharmacology*; D016971:Citrobacter freundii / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D027081:DNA Gyrase; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D004756:Enterobacteriaceae Infections / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D016133:Polymerase Chain Reaction / Q000379:methods
chemical_list: D000890:Anti-Infective Agents; D001425:Bacterial Outer Membrane Proteins; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II