Extended spectrum beta-lactamase mediated resistance in urinary tract isolates of family Enterobacteriaceae.

Extended spectrum beta-lactamases (ESBL) hydrolyse expanded spectrum cephalosporins like ceftazidime, cefotaxime and monobactam aztreonam. ESBL producing bacteria may not be detectable in the routine disk diffusion susceptibility tests leading to inappropriate use of antibiotics and treatment failures. As information on ESBL producers causing urinary tract infection (UTI) is not available from our country, the occurrence of ESBL producing strains causing UTI was studied as also the differences between the antimicrobial susceptibility patterns of ESBL and non-ESBL producers.Urinary isolates (233) were tested for antimicrobial susceptibility by Stoke's method and ESBL production by double disk diffusion method (ceftazidime and clavulanic acid). The clinical and demographic profile of the patients was noted.Sixty two of the 233 isolates tested (26.6%) were ESBL producers. Approximately 38.5 per cent of Klebsiellae, 24.7 per cent of Escherichia coli, 24 per cent of Enterobacter aerogenes, 33.3 per cent of Proteus sp. and the only Citrobacter strain produced ESBL. Recent surgery was found to be a significant (P < 0.01) risk factor for acquisition of ESBLs. Approximately 30 per cent of the ESBL producers appeared falsely sensitive or moderately sensitive to cefotaxime/ceftazidime in routine susceptibility testing. There was no difference between the ESBL producers and non-producers in the susceptibility to non-beta lactam agents except for gentamicin.A high percentage of urinary tract isolates produced ESBL. Since they are likely to be missed in routine disk diffusion susceptibility tests, all microbiology laboratories should look for ESBL production routinely to avoid treatment failures.