Phenotypic screening of metallo--lactamase in multi-drug-resistant Pseudomonas aeruginosa using a combined disk diffusion method

Clinical utilization of carbapenems remains under threat with the emergence of acquired carbapenemase-producing bacteria, particularly metallo-β-lactamases (MBL). Pseudomonas aeruginosa which is an important opportunistic pathogen causing nosocomial infections is potentially resistant to different broad-spectrum antibiotics due to its ability to produce metallo-β-lactamase (MBL). In the present 1 year study, 105 isolates of multidrug-resistant (MDR) P. aeruginosa were collected from Motahari, Milad and Taleghani hospital laboratories in Tehran. These isolates were screened by the disc diffusion and combined disc methods (imipenem + EDTA; meropenem + EDTA) to determine the capacity of producing MBL. The overall prevalence of MBL-positive isolates was 88.27% using imipenem and imipenem plus ethylene diamine tetra-acetic acid (EDTA) discs, meanwhile 92.73% of 55 randomly selected isolates evaluated phenotypically for the presence of an MBL, using meropenem and meropenem plus EDTA discs as well, were MBL positive. In the light of our results, the rapidly spreading resistance among bacterial populations due to the extensive use of antibiotics is a matter of concern for the optimal treatment of patients and the determination of MBL production of MDR P. aeruginosa strains using a simple, reliable and inexpensive testing method is essential in patients suffering from resistant infections.