Selection of oxacillin resistance in oxacillin-sensitive Staphylococcus aureus through exposure to ciprofloxacin but not piperacillin/tazobactam.
Ten oxacillin-sensitive Staphylococcus aureus strains were grown on agar containing four times their ciprofloxacin MIC to determine if exposure to ciprofloxacin would increase their resistance to oxacillin. All strains grew on the ciprofloxacin-containing agar and subsequently grew on oxacillin-salt agar. The geometric mean MICs for oxacillin increased one- to sixteen-fold and remained elevated after ten passages on antibiotic-free agar. The mecA gene was not detected in any strain. There was no increase in oxacillin MICs when the bacteria were passaged on agar containing four times their MIC of piperacillin/tazobactam. Exposure of oxacillin-sensitive strains of Staphylococcus aureus to ciprofloxacin may increase their MICs to oxacillin.
Evans
M E
ME
Department of Internal Medicine, University of Kentucky School of Medicine, Division of Infectious Diseases, Room MN 672 UKMC, 800 Rose Street, Lexington, KY 40536-0298, USA. meevanl@uky.edu
D000890:Anti-Infective Agents / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004359:Drug Therapy, Combination / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology*; D010397:Penicillanic Acid / Q000031:analogs & derivatives / Q000494:pharmacology*; D010406:Penicillins / Q000494:pharmacology; D010878:Piperacillin / Q000494:pharmacology*; D000077725:Piperacillin, Tazobactam Drug Combination; D012641:Selection, Genetic; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology*
D000890:Anti-Infective Agents; D010406:Penicillins; D000077725:Piperacillin, Tazobactam Drug Combination; D002939:Ciprofloxacin; D010397:Penicillanic Acid; D010068:Oxacillin; D010878:Piperacillin