Molecular Epidemiology of Clinical Pseudomonas aeruginosa Isolates Carrying IMP-1 Metallo- β -Lactamase Gene in a University Hospital in Turkey

Pseudomonas aeruginosa isolates carrying IMP- or VIM-type metallo-β-lactamase (MBL) have been increasingly reported in hospitals worldwide. One hundred P. aeruginosa clinical isolates from unrelated inpatients hospitalized at a Turkish university hospital were screened for the presence of bla_IMP and bla_VIM genes by polymerase chain reaction (PCR). One (1%) isolate was found to carry a VIM-type MBL gene, whereas nine (9%) carried an IMP-1 MBL gene carried on a cassette inserted into a class 1 integron. Only four of the IMP producers were detected as MBL producers according to E-test MBL. Minimum inhibitory concentrations (MICs) of imipenem for the IMP-1 and VIM-type MBL-producers were highly variable (MIC values, 8–128 μg/ml). Imipenem resistance was not plasmid-mediated according to the transformation assays. Piperacillin/tazobactam was the only effective drug in antimicrobial susceptibility testing. No aztreonam-resistant IMP and VIM producers were detected to produce an extended-spectrum β-lactamase (ESBL). Three class 1 integrons of approximately 2,300 bp, 1,800 bp, and 1,500 bp in size were detected in each of the nine IMP-positive isolates. Sequencing revealed three novel gene cassette arrays, aac(3)-1c–cmlA5, bla_IMP-1–aadA7-like, and aacA7–smr-2–orfD. Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) indicated that a clonal spread of IMP-1-producers had occurred in this hospital.