Molecular analysis of the integrons of metallo-β-lactamase-producing Pseudomonas aeruginosa isolates collected by nationwide surveillance programs across Japan

BACKGROUND: We investigate the evolving molecular epidemiology of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa isolates collected in a 100 institution, nationwide surveillance study in Japan from 2004 to 2006. RESULTS: MBL-producers were detected in 23/996 isolates (2.3%) in 2004 and 21/992 (2.1%) in 2006. Antimicrobial resistance (specifically, carbapenem resistance) rates between two periods did not differ significantly. MBL-producers were more prevalent in urinary tract isolates. bla(IMP-1) group was the most predominant (38 isolates, 80%), followed by 3 bla(IMP-7), 2 bla(IMP-11) group, and 1 bla(VIM-1). All MBL genes were identified in 16 different class 1 integrons, most of which were novel to INTEGRALL database. A total of 17 isolates of sequence type (ST) 235, a recognized worldwide drug-resistant lineage, were distributed in 5 geographic regions across Japan. ST235 isolates included a sublineage associated with In113-like integron. ST357 was identified in 14 isolates, 9 of which harboring a sole bla(IMP-1) gene cassette (In994) were recovered from Chugoku region in 2004. ST357 isolates with bla(IMP-11) group or ST235 with bla(IMP-7) emerged in 2006. We also report for the first time the presence of novel fosI gene cassette in strains other than Mycobacterium spp. CONCLUSIONS: Our data give an important “snapshot” of the molecular characteristics and dynamics of MBL-producing lineages in P. aeruginosa in Japan. The significant association of specific genotypes and integrons implies that dissemination and transmission of the preexisting resistant lineage, rather than horizontal gene transfer in situ, might largely explain their endemicity.