CHARACTERIZATION OF DNA GYRASE AND MEASUREMENT OF DRUG ACCUMULATION IN CLINICAL ISOLATES OF ACINETOBACTER-BAUMANNII RESISTANT TO FLUOROQUINOLONES

Twelve clinical isolates of Acinetobacter baumannii highly resistant t o pefloxacin (MIG greater than or equal to 32 mg/L) and to ciprofloxac in (MIC greater than or equal to 16 mg/L), were studied. A susceptible isolate used as a reference (MIG of 0.032 and 0.25 mg/L for ciproflox acin and pefloxacin, respectively) accumulated 85 mg of pefloxacin per litre of cell volume within 10 min, from a solution containing 10 mg/ L of antibiotic. One resistant isolate accumulated the same amount of pefloxacin, while the 11 others accumulated between 40 and 70 mg/L of cell volume. The differences between reference and resistant isolates with respect to ciprofloxacin and sparfloxacin accumulation were less pronounced. There were no apparent differences in the outer membrane p rotein profiles of susceptible and resistant isolates. DNA gyrase was isolated from four A. baumannii and the minimum concentration of fluor oquinolones, required to inhibit gyrase-catalysed supercoiling of plas mid DNA was 5- to 80-fold higher for the resistant isolates than for t he reference strain. Although most isolates showed some degree of redu ced fluoroquinolone accumulation, a DNA gyrase mutation was more likel y to be the main mechanism of the high level resistance encountered.