Metallo– β – lactamase producing nonfermentative gram–negative bacteria: An increasing clinical threat among hospitalized patients

ObjectiveTo detect and evaluate the various methods for metallo- β -lactamases (MBL) production in Pseudomonas aeruginosa (P. aeruginosa) and Acinetobacter species.MethodsA total of 109 P. aeruginosa and 85 Acinetobacter species were screened for imipenem resistance by Kirby-Bauer disc diffusion methods. Detection of MBL production was done by imipenem-EDTA combined disc test, double disc synerygy test (DDST) and imipenem-EDTA MBL E test.ResultsA total of 63 (57.8%) strains of P. aeruginosa and 46 (54.1%) strains of Acinetobacter spp. were found to be resistant to imipenem. Of the 63 imipenem resistant P. aeruginosa tested for MBL production, 44 (69.8%) were found to be positive and among 46 imipenem resistant Acinetobacter, 19 (41.3%) were shown to be the MBL producers.ConclusionsImipenem-EDTA combined disc test and MBL E test are equally effective for MBL detection in both P. aeruginosa and Acinetobacter spp., but given the cost-constraints, combined disc can be used as a convenient screening method in the clinical microbiology laboratory.