[Research regarding extended-spectrum beta-lactamases produced by enterobacteria strains].

Aim: To evaluate the susceptiblity of extended spectrum beta-lactamase (ESBL) producing organisms among Escherichia coli and Klebsiella pneumoniae, isolated between January-October 2009 from hospital and community.

Materials And Methods: From 611 enterobacteria strains, for 112 strains (E. coli, n = 84 and K. pneumoniae, n = 28), the ESBL phenotypic confirmation was performed with double disk test (DDT) and the replacement disk method. The minimum inhibitory concentrations (MICs) for next antimicrobial agents tested: ceftazidime, cefotaxime, ceftriaxone, cefepime, cefpirome, imipenem, meropenem, ertapenem, moxifloxacin, gatifloxacin, levofloxacin, ofloxacin were performed by agar dilution method. Resistance rates were reported using the Clinical Laboratory Standard Institute (CLSI) breakpoints for the fully susceptible category; moderately susceptible isolates were classified as resistant. K. pneumoniae ATCC 700603 and E. coli ATCC 25922 were used for quality control.

Results: Resistance rates for ceftazidime, cefotaxime, ceftriaxone and aztreonam among tested strains were very high: 84.5%, 100%, 100% and 96.4% for E. coli and 98.8%, 98.8%, 97.6% and 89.2% for K. pneumoniae, with the MIC90 values > 256 mg/L for either antimicrobial tested agent. The MICs for fourth generation cephalosporins ranges from 4 mg/L to 512 mg/L. The MICs for tested quinolones were > 2 mg/L for 89.2% strains. Using breakpoint for susceptibility, all isolates were sensitive to ertapenem, imipenem and meropenem.

Conclusions: We noticed a high resistance rate for ceftazidime, cefotaxime, ceftriaxone and aztreonam. In this study, carbapenems demonstrated the highest degree of activity.