Aim of the study was to evaluate the relationship between usage of antimicrobial agents intended to treat infection caused by Gram-negative bacteria (cefotaxim, ceftazidim, ofloxacin, ciprofloxacin, imipenem, meropenem, gentamicin, amikacin, netilmicin and amoxycilin/clavulanic acid) and resistance of those bacteria in the haemato-oncology unit at the University Hospital. Methods design: Observational, retrospective study. Data had been collected from January 1, 1998 to December 31, 2001. Antibiotic usage data were obtained by chart extraction. Non-duplicate strains isolated from haemato-oncology inpatients were tested for their susceptibility by the disk diffusion test. Results: A relationship between relative one-year consumption (expressed in DDD/lOObed-days) and rates of resistance for selected Gram-negative bacteria was evaluated by the means of linear regression. We identified statistically significant positive correlation for fluoroquinolones usage and Enterobacter spp. resistance (r = 0,821; p = 0,005). Statistically significant negative correlation was found for usage of gentamicin (r = -0,882; p = 0,012) and Klebsiella pneumoniae resistance. Conclusion: In the haemato-oncology setting a decrease of selective pressure of fluoroquinolones entailed a decrease of Enterobacter spp. strains resistant to fluoroquinolones. In paradox, hign resistance of Klebsiella pneumoniae strains to gentamicin was observed at the haemato-oncology wards with low consumption of gentamicin.

        Key words: antibiotics, antibiotic selective pressure, gram-negative bacteria, haemato-oncology