Prevalence and Susceptibility of extended spectrum beta-lactamases in urinary isolates of Escherichia coli in a Tertiary Care Hospital, Chennai- South India

Extended spectrum beta - lactamases (ESBLs) are on the rise in hospital settings across the globe. The presence of ESBLs significantly affects the outcome of an infection and poses a challenge to the management of infection worldwide. Therefore, the aim of the present study is to determine the prevalence and susceptibility of extended spectrum beta - lactamase in urinary isolates of Escherichia coli (E.coli) in a tertiary care hospital, Chennai-South India. A total of 450 urinary isolates of E.coli were collected over a period of six months from April 2008 to September 2008. Antimicrobial susceptibility testing was determined to commonly used antibiotics using the modified Kirby-Bauer's disc diffusion method. ESBL detection was done by the screening method of double disc synergy test and then confirmed by the phenotypic confirmatory test with combination disc as recommended by the Clinical Laboratory Standards Institute (CLSI) and the minimum inhibitory concentration (MIC) method using the E test strips (AB Biodisk,Sweden )- as per manufacturer's instructions. The prevalence of E.coli ESBL was 60%. The ESBL producing isolates were significantly resistant (p < 0.01) to ampicillin, trimethoprim / sulfamethoxazole, norfloxacin and nalidixic acid as compared to non-ESBL producers. Multidrug resistance was significantly (p < 0.01) higher (69%) in ESBL positive isolates than non-ESBL isolates (21%). Knowledge of the prevalence of ESBL and resistance pattern of bacterial isolates in a geographical area will help the clinicians to formulate the guidelines for antibiotic therapy to avoid inappropriate use of extended spectrum cephalosporins.