Prevalence and characterization of metallo-beta-lactamases in clinical isolates of Pseudomonas aeruginosa

The prevalence and the type(s) of metallo-beta-lactamases (MBLs) produced by isolates of Pseudomonas aeruginosa were investigated. During 2001, 506 nonduplicate isolates were obtained from hospitalized patients. Eighty-two strains were selected because of resistance to carbapenems and/or ceftazidime. Screening for MBL production was performed in the latter isolates by the Etest MBL strips (AB Biodisk, Solna, Sweden) and by a broth microdilution method measuring minimum inhibitory concentrations (MICs) of imipenem alone and in the presence of metal-chelating agents (EDTA and o-phenanthroline). Specific DNA probes were used to investigate the presence of genes coding for IMP- or VIM-type enzymes. Overall, four isolates of P. aeruginosa (obtained from independent patients) were found to carry a blaVIM gene. Polymerase chain reaction (PCR) experiments and DNA sequencing revealed that the VIM-2 determinant was present in three cases, whereas VIM-1 was detected in one isolate. Surveillance programs should be adopted to avoid the spread of these worrisome resistance genes