Increase in quinolone resistance in a Haemophilus influenzae strain isolated from a patient with recurrent respiratory infections treated with ofloxacin

The increase in the level of quinolone resistance of Haemophilus influenzae clinical isolates during ofloxacin therapy of a patient with recurrent res piratory infections was investigated. The first isolate (MIC of ciprofloxac in of 2 mu g/ml) and the second isolate (MIC of 32 mu g/ml) belonged to the same clone, as shown by pulsed-field gel electrophoresis, and the increase in the resistance level was associated with a substitution in Ser-84 to Ar g in the ParC protein. These results emphasize the potential risk of develo pment of quinolone-resistant H. influenzae during fluoroquinolone therapy i n patients with recurrent respiratory infection.