Molecular detection and characterisation of Metallo-β-Lactamase (MBL) Genes and integrons of Imipenem –Resistant Pseudomonas aeruginosa

The increase in the prevalence of carbapenem-resistant Pseudomonas aeruginosa isolates, particularly caused by the metallo-ß-lactamases (MBL) is of great concern in the clinical settings worldwide. Here, we report the detection and identification of MBL producing P. aeruginosa in our hospital (University Malaya Medical Center, Malaysia), and the characterization of MBL cassette-containing integrons in 90 imipenem-resistant P. aeruginosa isolates. Of the isolates investigated in this study, 32 (94%) MBL-positive strains were identified, harboring either blaIMP or blaVIM genes. Three MBL phenotypic assays methods (CDT, DDST, and IP/IPI E-test) were evaluated by comparison to that of molecular methods. The MBL IP/IPI E-test exhibited 100% accuracy in the detection of MBL production. Class1 integrons were detected as the most abundant type of integron in the Malaysian isolates. The genes detected from MBL-positive isolates were blaIMP-7, aacC1; blaVIM-11; aacA7, blaVIM-2, attI, and aacA7. Our findings show that class I integrons were prevalent in P. aeruginosa and they may play an important role in the dissemination of multidrug resistance P. aeruginosa. Based on the differences in the fingerprinting patterns, two clusters (A and B) were identified among the MBL-producing isolates. Cluster A comprised 18 isolates (56 %) carrying the blaVIM gene, whereas cluster B comprised 14 (44 %) isolates carrying the blaIMP gene. The non-MBL isolates were divided into clusters C and D. Cluster C comprised 22 non-MBL isolates harbouring class 1 integrons, whilst cluster D consisted of three isolates carrying class 2 integrons.