Phenotypic detection of Extended Spectrum Beta-Lactamases and Amp C Beta- Lactamases among nosocomial isolates in a tertiary care hospital.
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Date
2013-10
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Abstract
Background & objectives: Extended-Spectrum Beta-Lactamases (ESBLs) is an important resistance
mechanism in Enterobacteriaceae infections. Lack of standard guidelines from Clinical Laboratory
Standards Institute (CLSI) for Amp C beta-lactamase detection poses a problem. This study was undertaken
to detect ESBLs by phenotypic tests and Amp C beta-lactamase by inhibitor based method. Material
and Methods: 200 consecutive non-repetitive isolates of E.coli, Klebsiella and Proteus from clinical samples
were screened for ESBLs as per CLSI guidelines and confirmed by PCDT, DDST and E-tests (AB
Biodisk, Biomerieux). Amp C beta lactamases were screened by cefoxitin resistance and confirmed by
inhibitor (Cloxacillin) based method. Simultaneous occurrence of Amp C and ESBLs was detected by
combined disk test (Neo-Sensitabs and Diatabs). Descriptive and Kappa statistics were used. Results: Out
of 200 isolates studied, 131 were initially screened as ESBL producers and later 114 (57%) were confirmed
by phenotypic methods. E-Test was found most sensitive phenotypic test as compared to PCDT
and DDST. 13 strains resistant to cefoxitin (30μg) were found to be pure Amp C producers. Combined
disk test detected 36 to be ESBL and Amp C co-producers. Surprisingly, six isolates found sensitive to
cefoxitin disk were confirmed as Amp C producers by cloxacillin disk inhibition test. Conclusion: 57%
ESBLs and 27.5% Amp C producers were isolated from nosocomial pathogens showing significant resistance
to 3rd generation cephalosporins. Phenotypic confirmation by E-test, PCDT & DDST were useful
for ESBL identification and for detection of Amp C, cloxacillin was found to be an effective inhibitor.
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Keywords
Amp C beta-lactamases, beta- lactamase/ beta- lactamase inhibitor combinations, Extended spectrum beta-lactamases, inhibitor based tests
Citation
Vijayvergia V, Sahni A K, Lall M, Vijay K, Khan I D. Phenotypic detection of Extended Spectrum Beta-Lactamases and Amp C Beta- Lactamases among nosocomial isolates in a tertiary care hospital. Bangladesh Journal of Medical Science. 2013; 12(4): 378-384.