title: Analysis of the mechanism of quinolone resistance in nalidixic acid-resistant clinical isolates of Salmonella serotype Typhimurium.
abstract: Over a period of 2.5 years, 42 cases of gastro-enteritis caused by nalidixic acid-resistant Salmonella serotype Typhimurium occurred in Malaga. The epidemiological relationship among the strains involved was investigated by analysis of plasmid profile and of chromosomal DNA by pulsed-field gel electrophoresis (PFGE). Despite having different plasmid profiles, all 42 nalidixic-acid resistant Typhimurium isolates had evolved from one clone as shown by analysis of chromosomal DNA by PFGE. The mechanism of quinolone resistance in these Typhimurium isolates was also investigated. Analysis of outer-membrane proteins and lipopolysaccharide from quinolone-susceptible and resistant clinical isolates tested showed no differences. All nalidixic acid-resistant isolates had MICs for ciprofloxacin of 0.25 mg/L and for nalidixic acid of 1024 mg/L. Polymerase chain reaction fragments of 285 bp, containing the quinolone resistance-determining region of the gyrA gene, and of 237 bp, containing the region of parC homologous to the quinolone resistance-determining region of the gyrA gene, were sequenced. All resistant isolates presented a change at Ser-83 to Phe in the GyrA protein, but no changes were observed in the ParC protein. These findings indicated that this mutation in gyrA plays a major role in the acquisition of nalidixic-acid resistance in clinical isolates of Typhimurium.
authors.affiliation: Department of Microbiology, School of Medicine, University of Barcelona, Villarroel, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Ruiz
authors.forename: D
authors.initials: D
authors.lastname: Castro
authors.forename: P
authors.initials: P
authors.lastname: Goñi
authors.forename: J A
authors.initials: JA
authors.lastname: Santamaria
authors.forename: J J
authors.initials: JJ
authors.lastname: Borrego
authors.forename: J
authors.initials: J
authors.lastname: Vila
mesh_terms: D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000378:metabolism / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis; D001483:Base Sequence; D002939:Ciprofloxacin / Q000378:metabolism / Q000494:pharmacology; D027081:DNA Gyrase; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004352:Drug Resistance, Microbial; D005243:Feces / Q000382:microbiology; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology*; D012480:Salmonella Infections / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013030:Spain
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