Extended-spectrum beta-lactamase producers: Detection for the diagnostic laboratory

Abstract

Background and Objectives: Discovered in 1983, Extended spectrum beta-lactamase (ESBL) producers are still the leading cause of infections in India. Its prompt detection is crucial to the clinical management. The Clinical Laboratory Standards Institute (CLSI) recommends phenotypic screening and confirmatory tests to identify the ESBL producer making it cost and time consuming for the diagnostic laboratory. We compare here the screening and confirmatory tests offering a solution to the CLSI recommendation. Methods: Nosocomial isolates E. coli (71) and K. pneumoniae (25) resistant to cefotaxime and ceftazidime were included. CLSI recommended testing with cefotaxime, ceftazidime and in combination with clavulanic acid by disk diffusion and agar dilution methods were performed. E-test was performed on discrepant results. To determine the genetic relatedness of the organisms, 22 Medical and Surgical ICU isolates were genotyped by PFGE. Dendrogram was constructed using dice co-efficient, UPGMA method with diversity database software. Results and Conclusions: Phenotypic screening disk diffusion test versus the confirmatory agar dilution MIC tests with cefotaxime and ceftazidime correlated well with the final ESBL status (kappa 0.852 and 0.905 P