engleski

Extended-spectrum beta-lactamase producing isolates of Enterobacteriaceae in a University Hospital, Zagreb, Croatia

Objectives The aim of the study was to determine the prevalence of ESBLs in Enterobacteriaceae isolates from hospitalized patients, their antibiotic susceptibilites and the transferability of resistance to oxymino-cephalosporins and aztreonam. Methods Bacteria Dodati broj i vrstu izolata, iz kojih materijala i s kojih odjela i bolnice? Stavi broj i zastupljenost sojeva na početak. In total 76 ESBL producers were investigated (27 Escherichia coli, 37 Klebsiella pneumoniae, 6 Proteus mirabilis, 4 Klebsiella oxytoca and 2 Enterobacter cloacae). Antibiotic susceptibilities of ESBL producing isolates and their E. coli transconjugants was determined by disk-diffusion and broth microdilution method according to NCCLS. Minimum inhibitory concentrations (MICS) were tested for: amoxycilline/clavulanic adid, piperacillin/tazobactam, ceftazidime alone and in combination with clavulanic acid, cefotaxime, ceftriaxone, aztreonam, cefepime, imipenem, meropenem, gentamicin and ciprofloxacin. Antibiotic susceptibilities to chloramphenicol, tetracycline and sulphametoxazole/trimethoprim (cotrimoxazole) was determined by disk-diffusion method. ESBLs were detected by double-disk synergy method and by ł8 fold reduction in ceftazidime MIC in the presence of clavulanate. Transferability of R plasmids was determined by conjugation (broth mating method) employing an E. coli A15 R- strain resistant to rifampicin as recipient. Frequency of conjugation was expressed relatively to the number of donor cells. Cotransfer of resistance to non beta-lactam antibiotics (aminoglycosides, tetracycline, chloramphenicol. and sulphametoxazole/trimethoprim) was tested as well. Results The percentage of ESBL producers was as follows: 3% of E. coli, 17% of K. pneumoniae, 2% of Proteus mirabilis and 1% of K. oxytoca. There was no resistance detected to imipenem, meropenem, cefoxitin and ciprofloxacin among E. coli isolates. 67% of these strains were resistant to amoxycillin/clavulanate and ceftazidime, 70% to aztreonam and 78% to gentamicin. All K. pneumoniae strains were susceptible to imipenem, meropenem and cefoxitin, but 78% of the strains were resistant to ciprofloxacin, 86% to amoxycillin/clavulanic acid and 92% to aztreonam. All K. pneumoniae isolates were resistant to cefazidime. 38% of K. pneumoniae strains transferred the plasmid encoding ESBL to E. coli recipient with the frequency ranging from 10-5 to 10-9. Transfer of plasmid was successful in 96% of E. coli isolates with the frequency of 10-5 to 10-10. Only 17% of P. mirabilis strains transferrred ceftazidime resistance to E. coli recipient with at a very low frequency (10-8). Contrary to that, all E. cloacae and K. oxytoca strains sucessfully transferred the plasmid. Transconjugants had similar resistance patterns to beta-lactam antibiotics as their respective donors. The resistance genes to non-beta-lactam antibiotics were cotransferred alongside with ceftazidime resistance in all K. oxytoca and E. coli strains. In. K. pneumoniae resistance to cotrimoxazole and chloramphenicol was cotransferred in 10% of the strains, to gentamicin in 70% of the strains and to tetracycline in 75% of the strains. Conclusions The prevalence of ESBL isolates is in concordance with the prevalence at the national level. No resistance to carbepenems among Enterobacteriaceae was observed so far, but since ESBL positive K. pneumoniae isolates resistant to carbapenems have been described elsewhere it is likely to expect that such strains will appear in Croatia in the future. Further analysis of the type of beta-lactamase is necessary.

extended-spectrum beta-lactamases; Enterobacteriaceae; resistance

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