[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.