Detection of metallo-beta-lactamase producing Pseudomonas aeruginosa using a modified IMP-lysate assay

Abstract

Since the increasing prevalence of carbapenem-resistant Pseudomonas aeruginosa spp., accurate detection of metallo-β-lactamase (MBL) such as bla_VIM type enzyme producing isolates became very important. However, phenotypic MBL detection methods previously reported are not highly sensitive or highly specific. This study aimed to evaluate the performance of a modified IMP-lysate test, the doubledisk- synergy-test (DDST) and the combined-disk-test (CDT) for detecting MBL bla_VIM gene in P. aeruginosa. The reference technique was PCR molecular test. The study used 12 blaVIM2 producer isolates, 13 MBL-negative controls which included 4 imipenem-susceptible strains and 9 imipenemresistant strains harbouring bla_SHV-2a genes collected from two Tunisian hospitals and P. aeruginosa ATCC27853 and P. aeruginosa COL-1 as negative and positive controls respectively. CDT showed 100% of sensitivity. The highest level of specificity was shown by IMP-lysate test (76.92%). To evaluate efficiencies of methods, the study noted that the highest Youden Index (YI) was shown by IMP-lysate method (0.7), followed by DDST (0.6) than CDT (0.2). Since MBL-Etest and PCR were expensive and not adaptable for extension use in clinical microbiology laboratories, a modified IMP-lysate MBL hydrolytic activity can be chosen by laboratories with limited resources as an inexpensive, simple, and accurate test to detect . P. aeruginosa producing bla_VIM enzyme.

Key words: Metallo-beta-lactamase, VIM, phenotypic detection, pseudomonas aeruginosa.