The Occurrence of CTX-M3 Type
Extended Spectrum Beta Lactamases among Escherichia Coli Causing Urinary Tract Infections in a Tertiary Care Hospital
Dr. Malini A. Bhat
Associate Professor, Dept of Microbiology,
Indira Gandhi Medical College & Research Institute,
Vazhudavur Road, Kadirkammam, Puducherry-605009 (India).
Introduction: The Extended Spectrum Beta Lactamases (ESBLs) are the class A plasmid mediated enzymes that hydrolyze the oxyimino-cephalosporins and the monobactams but not the cephamycins and they are inhibited by clavulanic acid. In the recent years, the CTX-M type are the most common ESBLs which have been isolated. The present study was undertaken to know the prevalence of the ESBL producing E. coli in urinary tract infections (UTIs) and also to know the occurrence of the CTX-M3 genotype among these E. coli which were isolated in our hospital.
Materials and Methods: The routine antimicrobial susceptibility testing was done for the E. coli which were isolated from the urine samples. The strains of E. coli that were resistant to cefotaxime and ceftriaxone were selected for the ESBL testing. The strains were tested for ESBL production by the Double Disc Synergy Test (DDST) and the phenotypic confirmatory double disc test (PCDDT) as per the CLSI guidelines. Fifty four isolates of E. coli were found to be positive for ESBL by the phenotypic methods, out of which fifty isolates were tested for the presence of CTX-M3 by PCR and also their minimum inhibitory concentrations (MICs) for ceftazidime were determined.
Results: Out of a total of 157 E. coli isolates, 54 isolates (34.4%) were found to be positive for ESBL by the phenotypic methods, DDST and PCDDT. Nearly 21(38.8%) ESBL positive E. coli isolates had an MIC of ≥ 128μg/ml for ceftazidime. Out of the 50 strains of ESBL positive E. coli that were run for PCR, 42(84%) were positive for the CTX-M3 gene.
Conclusion: Our study showed that the ESBL producing urinary isolates of E. coli were not only resistant to the third generation cephalosporins but also to ciprofloxacin, cotrimoxazole and gentamicin. The occurrence of the CTX-M3 genotype was high among the E. coli isolates in our study.