Prevalence of Imipenemase and Verona Integron-Encoded Metalloβ-Lactamase in Imipenem-Resistant Pseudomonas aeruginosa

Abstract

Objective: To determine the prevalence of metallo-β-lactamase (MBL) including imipenemase (IMP) and Verona integronencoded metallo-β-lactamase (VIM) in imipenem-resistant Pseudomonas aeruginosa (IRPA) isolates and investigate the in vitro activities of 9 antimicrobial agents against MBL-positive isolates. Material and Methods: Seventy-eight IRPA isolates were obtained from Songklanagarind Hospital. MBL production was detected by the combined-disk test, and the blaIMP and blaVIM genes were determined via Polymerase Chain Reaction (PCR). The in vitro activities of amikacin, gentamicin, aztreonam, ceftazidime, meropenem, ciprofloxacin, colistin, piperacillin/ tazobactam, and ticarcillin/clavulanate were determined using the E-test method. Results: Of the 78 IRPA isolates, 20 (25.6%, 95% CI 17.2-36.4%) were MBL phenotype-positive, and 30 (38.5%, 95% CI 28.5-49.6%) were MBL genotype-positive (29 Imipenemase (IMP)-type and 1 Verona integron-encoded metallo-βlactamase (VIM)-type). Ninety percent of the MBL genotype-positive isolates were MDR. Most MBL genotype- positive isolates were susceptible to colistin (susceptibility rate of 96.7% and MIC50 value of 1.5 µg/mL). Conclusion: Our results showed a high prevalence of MBL-positive isolates (38.5%) in IRPAs, and the IMP-type isolates were dominant among the metallo-β-lactamase-producing imipenem-resistant P. aeruginosa tested. Most MBL-positive isolates were susceptible to colistin and had low MIC50 values.