Chlorhexidine hypersensitivity of ciprofloxacin-resistant variants of Pseudonwnas aeruginosa PAO

Examination of 67 ciprofloxacin-resistant clones of Pseudomonas aeruginosa PAO (ciprofloxacin MIC > 0.5 mg/L) yielded four isolates that were hypersensitive to chlorhexidine (MIC 5 mg/L); none was found among 179 ciprofloxacin-sensitive colonies. Revertant studies and the introduction of a wild-type Escherichia coli DNA gyrase A gene confirmed that ciprofloxacin resistance and chlorhexidine hypersensitivity were not the result of a single mutation. Mutagenicity testing of ciprofloxacin showed no evidence for the supposition that chlorhexidine hypersensitivity was the result of ciprofloxacin-induced mutation in P. aeruginosa PAO.