Resumo

Pseudomonas aeruginosa is a well-known nosocomial pathogen, responsible for a wide range of severe infections and able to become resistant to virtually all the antibiotics commercially available. Production of â-lactamases, such as class B metallo-beta-lactamases (MBLs) by P. aeruginosa isolates is a substantial concern to the antimicrobial therapy in hospitalized patients. The aim of this work was to detect MBL production in P. aeruginosa strains, to investigate the occurrence of bla_SPM and bla_IMP genes, to determine their susceptibility profiles and to analyze the isolates clonality. Were analyzed 20 samples from 2007 to 2009, obtained from three public hospitals. Antimicrobial susceptibility was performed according CLSI, 2010. The identification of MBL-producing isolates followed the method proposed by Arakawa et al. The detection of genes bla_SPM-1 and bla_IMP was performed by specific PCR. Molecular typing was carried out by PFGE and the clonal relation among the isolates was established in accordance with the criteria of Tenover. The results showed that only 20% (4/20) of the isolates were confirmed as MBL positives by phenotypic testing, despite the observed carbapenem resistance in most of them. The bla_SPM-1 gene was only found in these isolates (4/4). None of the tested samples had bla_IMP gene. Susceptibility results showed that 90% (18/20) of the isolates were fully resistant to imipenem and ceftazidime; 95% (19/20) to gentamicin and ciprofloxacin; 85% (17/20) to amikacin; 70% (14/20) to piperacilin/tazobactam and 85% (17/20) to aztreonam. All the isolates were susceptible to polimixin B. Macrorestriction patterns revealed the presence of a main clone (A) with two closely related subtypes (A1 and A2) between the four MBL positive isolates. By contrast, MBL negative were distinctly different, showing about ten non-related clones. These findings suggest that the production of MBL in the hospitals analyzed was mediated by a single epidemic clone, probably the widespread Brazilian clone. Moreover, an important finding was the high frequency of non-related and pan-resistant P. aeruginosa strains, which seems to be replacing the SPM clone in the hospitals studied.