Aims: Drug resistance enzymes like beta-lactamases and Extended-Spectrum Beta-
Lactamases (ESBLs) are mostly produced in the response of mutation and a few other factors. These
enzymes are plasmid-mediated that can confer resistance against several β-lactam agents including
cephalosporin and extended-spectrum cephalosporin. This study is conducted to determine the frequency
of ESBL producing Klebsiella strains and to compare the phenotypic detection methods among various
clinical samples collected from a commercial centralized Microbiology diagnostic laboratory.
Materials and Methods: 125 Klebsiella strains were collected for this study. After identification
and susceptibility testing, the phenotypic characterization of ESBL producing K. pneumoniae
(n=89) and K. oxytoca (n=36) species was performed by using the double disc synergy test and the
combination disc test.
Results: In our study, 80 (64%) Klebsiella isolates were found to be ESBL positive due to their
ability to produce an extended zone of inhibition with combination disc whereas 45 (36%) isolates
were ESBL negative with no extended zone of inhibition. The phenotypic findings obtained by using
the combination disc method and double disc synergy method were re-confirmed by molecular
methods. By comparing the phenotypic finding with the genotypic results, we identified 80 (64%)
Klebsiella isolates as ESBL positive and 45 (36%) isolates as ESBL negative. These genotypic
findings of the ESBL producing strains were similar to the results obtained from the combination
disc method. It also confirmed that the double disc synergy test was unable to detect 47 ESBL producing
Conclusion: For implementing strict infection control policy and to stop the spread of resistant
strains, it is important to detect ESBL producing isolates more rapidly. A suitable antimicrobial
therapy can be started timely with the early detection of resistance enzymes either phenotypically
or genotypically. It has been proved that the combination disc test can be used more reliably and
preferably as compared to the double disc synergy test for the detection of ESBL enzymes produced
by Klebsiella strains.