Induction of resistance to fluoroquinolones in clinical and environmental isolates of Pseudomonas aeruginosa.

An attempt to induce resistance to ciprofloxacin in vitro was made against clinical and environmental isolates of Pseudomonas aeruginosa. This in vitro manipulation of strains resulted in the increase of minimum inhibitory concentration from 0.4 microg/ml to 1 microg/ml of the original strains to 9.0 to 12.5 microg/ml indicating development of resistance to ciprofloxacin and a major decrease in the size of zone diameters of norfloxacin and ofloxacin indicating cross resistance to these agents. Results indicate the induced resistance to ciprofloxacin can promote development of cross resistance to other fluoroquinolones. This suggests that caution should be taken while using fluoroquinolones for the treatment of Pseudomonas aeruginosa infections.