Development of resistance to ciprofloxacin in nutrient-rich and nutrient-limited growth conditions in vitro by Pseudomonas aeruginosa isolates from patients with cystic fibrosis

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Abstract
Five serial exposures of mucoid Pseudomonas aeruginosa from patients with cystic fibrosis to subinhibitory concentrations of ciprofloxacin resulted in stepwise increases in the MIC, with a mean proportional increase of 10. MICs were significantly lower in an iron-limited chemically defined medium than in Iso-Sensitest broth. The mucoid phenotype was maintained in chemically defined medium. Acquired resistance was retained either partially or completely in 85% of the isolates following 10 transfers in drug-free media. In cases in which susceptibility was regained, an increase in the MIC was observed on one further exposure to ciprofloxacin.