Genetic and Biochemical Characterization of an Acquired Subgroup B3 Metallo-β-Lactamase Gene,blaAIM-1, and Its Unique Genetic Context in Pseudomonas aeruginosa from Australia

Abstract

ABSTRACTThree clinicalPseudomonas aeruginosaisolates (WCH2677, WCH2813, and WCH2837) isolated from the Women's and Children's Hospital, Adelaide, Australia, produced a metallo-β-lactamase (MBL)-positive Etest result. All isolates were PCR negative for known MBL genes. A gene bank was created, and an MBL gene, designatedblaAIM-1, was cloned and fully characterized. The encoded enzyme, AIM-1, is a group B3 MBL that has the highest level of identity to THIN-B and L1. It is chromosomal and flanked by two copies (one intact and one truncated) of an ISCRelement, ISCR15. Southern hybridization studies indicated the movement of both ISCR15andblaAIM-1within the three different clinical isolates. AIM-1 hydrolyzes most β-lactams, with the exception of aztreonam and, to a lesser extent, ceftazidime; however, it possesses significantly higherkcatvalues for cefepime and carbapenems than most other MBLs. AIM-1 was the first mobile group B3 enzyme detected and signals further problems for already beleaguered antimicrobial regimes to treat seriousP. aeruginosaand other Gram-negative infections.