RESUMEN
The present study was conducted to find the prevalence of Extended spectrum b Lactamase (ESBL) producing strains of Klebsiella pneumoniae (K. pneumoniae) and Escherichia coli (E. Coli) in different clinical samples received at the Department of Microbiology, Medical College Baroda. A total of 187 clinical isolates (106 of K. pneumoniae and 81 of E. Coli) were tested for resistance to any one of the three Third generation cephalosporins (3GC) namely cefotaxime, ceftazidime and ceftriaxone. 100 isolates (57 of K. pneumoniae and 43 of E. Coli) were found to be resistant to at least one of the 3GC tested. These were then tested for ESBL production by Double Disc Diffusion Synergy Test (DDST) using Ceftriaxone, Ceftazidime, and Cefotaxime along with Augmentin as well as by the MIC reduction test. ESBL was detected in 53 isolates (33 K. pneumoniae and 20 E. coli). Using the interpretative guidelines of the NCCLS, 24% to 27% of the ESBL isolates would have been reported to be susceptible to the 3GC by routine antimicrobial susceptibility methods. DDST was found to be a useful, simple and cost effective test for the detection of ESBL producing strains.