title: Effects of low-level ciprofloxacin challenge in the in vitro development of ciprofloxacin resistance in Campylobacter jejuni.
abstract: The effects on MIC values and the selection of different base substitutions in the quinolone resistance determining region (QRDR) of gyrA were studied on initially ciprofloxacin-susceptible Campylobacter jejuni strains by challenging them to 0.125 mg/L of ciprofloxacin. This ciprofloxacin challenge selected variants with ciprofloxacin MIC levels up to 32 mg/L. Repeated experiments under identical conditions resulted in different responses in MIC levels and alterations in the QRDR of gyrA. A characteristic outcome to ciprofloxacin challenges was the appearance of double peaks in the sequencing chromatograms of QRDR. This finding suggested the coexistence of subpopulations possessing Thr86 --> Ile and/or Asp90 --> Asn mutations alongside the unmutated parent population. In some cases, bacterial variants expressing ciprofloxacin-resistant phenotypes possessed no mutations in their QRDR. These variants were prone to regain susceptibility to ciprofloxacin rapidly after the removal of the selection pressure, whereas the QRDR-mutated variants persisted over several subcultivations in a medium without ciprofloxacin. In conclusion, a low ciprofloxacin concentration of 0.125 mg/L selects a variety of QRDR mutations and also a QRDR-independent resistance mechanism, which may coexist with each other in a C. jejuni population. Persistent ciprofloxacin challenge selects Thr86 --> Ile and/or Asp90 --> Asn mutants.
authors: Department of Food and Environmental Hygiene, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland. minna.hannula@helsinki.fi
authors: Minna
authors: M
authors: Hannula
authors: Marja-Liisa
authors: ML
authors: Hänninen
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000008:administration & dosage / Q000494:pharmacology*; D001483:Base Sequence; D016123:Campylobacter jejuni / Q000187:drug effects* / Q000302:isolation & purification; D002645:Chickens; D002939:Ciprofloxacin / Q000008:administration & dosage / Q000494:pharmacology*; D027081:DNA Gyrase / Q000187:drug effects / Q000378:metabolism; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation
chemical_list: D000890:Anti-Infective Agents; D004269:DNA, Bacterial; D002939:Ciprofloxacin; D027081:DNA Gyrase