Hospital outbreak of multiple clones of Pseudomonas aeruginosa carrying the unrelated metallo-β-lactamase gene variants blaVIM-2 and blaVIM-4

Objectives: The possible contribution of metallo-beta-lactamases in the frequent detection of carbapenem-resistant Pseudomonas aeruginosa isolates in a tertiary Greek hospital in Central Greece was investigated. Materials and methods: All carbapenem-resistant (imipenem- and/or meropenem-resistant) P. aeruginosa isolates recovered from separate patients during a 1 year period in the Clinical Microbiology Laboratory at the University Hospital of Thessaly, Larissa, Greece, were studied for metallo-beta-lactamases. They were tested by Etest MBL, PCR analysis and nucleotide sequencing. DNA fingerprints were obtained by pulsed-field gel electrophoresis (PFGE) of XbaI-digested chromosomal DNA. Results: A bla(VIM) gene was detected in 47 of the 53 (88.7%) carbapenem-resistant P. aeruginosa isolates. PFGE grouped the bla(VIM)-positive isolates in six unrelated genotypes; one type included two subtypes. Nucleotide sequencing of the PCR amplicons of a randomly selected isolate from each one of the seven subtypes, detected the variant sequences bla(VIM-2) in four and bla(VIM-4) in three cases, respectively. They were carried as single gene cassettes or along with an aminoglycoside resistance gene (aacA29a) in class 1 integrons. Conclusions: These findings suggest that different strains of P. aeruginosa carrying unrelated metallo-beta-lactamase gene variants predominate in our hospital environment.