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Multiplex PCR for blaCTX-M & blaSHV in the extended spectrum beta lactamase (ESBL) producing Gram-negative isolates
Reprint requests: Dr S.A. Jemima, Research Scholar, Department of Microbiology, International Centre for Cardio Thoracic & Vascular Diseases, Frontier Lifeline Pvt Ltd, Dr K.M.Cherian Heart Foundation, R-30-C Ambattur Industrial Estate Road, Chennai 600 101, India e-mail: sam_jemi@yahoo.co.in
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Received: ,
Abstract
Background & objectives:
Phenotyping is commonly used for detection of extended spectrum beta lactamase (ESBL) production in Gram-negative isolates. ESBLs are mainly coded for by three important genes, namely blaTEM, blaSHV and blaCTX-M. In this study we used a multiplex PCR as a rapid method to identify two common genes (blaCTX-M & blaSHV) responsible for extended spectrum beta lactamase production in members of Enterobacteriaceae family isolated from different clinical samples from a specialty hospital at Chennai.
Methods:
A total of 260 non repetitive clinical isolates from 240 patients (some patients had more than one organism also), was selected for the study. Of these 33 were from sputum, 64 from urine, 46 from blood, 28 from pus aspirates, 58 from endotracheal secretions and 31 from other miscellaneous specimens. Phenotypic identification for ESBL production was confirmed by double disk synergy test (DDST) and phenotypic confirmatory double disk test (PCDDT) according to CLSI guidelines. Multiplex PCR for blaCTX-M and blaSHV was performed for the ESBL positive isolates.
Results:
bla SHV like genes were found in 6 of 42 E.coli (14%), 7 of 46 Enterobacter species (15%), 28 of 62 Klebsiella species (45%) and bla SHV was not detected in any of the 50 isolates of non-fermenting Gramnegative isolates. (Pseudomonas and Acinetobacter species) blaCTX-M like genes were found in 21 of 42 E. coli (50%), 13 of 46 Enterobacter species (28%), 25 of 62 (40%) Klebsiella species and 1 of 50 nonfermenting Gram-negative bacilli (2%).
Interpretation & conclusions:
Our study demonstrated rapid detection of blaSHV and blaCTX-M in isolates belonging to Enterobacteriaceae and other non-fermenting clinical isolates using multiplex PCR. This genotypic method provided a rapid and efficient differentiation of ESBLs in the laboratory.
