Laboratory Identification of Metallo-beta-lactamase Producing Clinical Isolates of Pseudomonas aeruginosa: An Assessment of Different Phenotypic Methods

Background: Multidrug Resistant (MDR) Pseudomonas aeruginosa, an emerging superbug causing a wide spectrum of nosocomial infections. Carbapenem resistance among P. aeruginosa isolates is of grave concern and is mainly due to production of Metallobeta- lactamase (MBL) enzymes. Aim and Objectives: To find out the prevalence of MBL producing P. aeruginosa isolates from various clinical samples and to evaluate the efficacy of different phenotypic tests employed in vitro for their detection. Material and Methods:Atotal of 358 P. aeruginosa strains obtained from different clinical samples were subjected to antimicrobial susceptibility testing by Kirby-Bauer's Disc Diffusion method. All the imipenem resistant isolates were further tested by Modified Hodge Test (MHT) to detect carbapenem resistance. MBL production was tested by screening with Combined Disc Test (CDT) and Double Disc Synergy Test (DDST). MBL production was confirmed by MBL Etest (Ab BioDisk). Results: Among 358 strains of P. aeruginosa recovered, 114 isolates showed resistance to imipenem. E test demonstrated 73 out of 114 isolates as MBL producers. Of MHT, CDT and DDST tests performed, DDST showed high sensitivity and specificity. Conclusion: DDST can be suggested as an economical option in place of expensive E test for routine screening of MDR P. aeruginosa isolates for MBL production in a clinical laboratory; which is crucial for planning better management protocols