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

Since the increasing prevalence of carbapenem-resistant Pseudomonas aeruginosa spp., accurate detection of metallo-β-lactamase (MBL) such as blaVIM 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 blaVIM 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 blaSHV-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 blaVIM enzyme.Key words: Metallo-beta-lactamase, VIM, phenotypic detection, pseudomonas aeruginosa