BACKGROUND: Bacteria of the Klebsiella genus may cause numerous infectionsin human, which are often treated with beta-lactam antibiotics. The fundamental mechanism of Klebsiellaresistance to penicillins or cephalosporins involves the production of enzymes--extended-spectrum beta-lactamases(ESBLs). Because of resistance of many Klebsiella spp. strains to beta-lactams, alternative antibiotictherapy can make use of aminoglycosides and quinolones. MATERIAL/METHODS: The study analyzed the prevalenceof ESBL -type enzymes among 256 Klebsiella pneumoniae strains isolated from various clinical materialscollected from patients hospitalized between 1997 and 2000. ESBLs were detected by double-disk synergytest (DDST). The prevalence of strains resistant to selected aminoglycosides (gentamicin, amikacin, netilmicin)and quinolones (ciprofloxacin, norfloxacin, nalidixic acid) in the particular years was analyzed. Drugsensitivity was determined by disk-diffusion method according to the recommendations of the NationalReference Center for Microbial Drug Sensitivity. RESULTS: During the analyzed time interval, a significantincrease of the number of K. pneumoniae ESBL(+) strains was noted: in 1997 - 16.5% (14/85) and in 2000- 40.4% (22/54) (p<0.001).Among the ESBL(+) strains, an increase of the number of strains resistant to the tested antibiotics, except for nalidixic acid, was demonstrated
Conclusion: A statistically significant increase of multidrug-resistant K. pneumoniae strains, including strains producing ESBLs, was demonstrated in the analyzed material

Keywords: amikacin, Anti-Bacterial Agents, Anti-Infective Agents, Ciprofloxacin, Drug Resistance, Microbial, Gentamicins, Klebsiella pneumoniae, Microbial Sensitivity Tests, Nalidixic Acid, Netilmicin, Norfloxacin, Prevalence, Time Factors, beta-Lactamases