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Microbiological and Epidemiological Characterization of Imipenem-Resistant Pseudomonas aeruginosa Strains from a Brazilian Tertiary Hospital: Report from the SENTRY Antimicrobial Surveillance Program

Abstract OBJECTIVES: To evaluate the antimicrobial susceptibility profile, the genetic similarity, and the mechanisms of carbapenem resistance among imipenem-resistant Pseudomonas aeruginosa isolates collected from a Brazilian tertiary teaching hospital. METHODS: Seventy-eight consecutive samples of P. aeruginosa were evaluated during 2000 and 2001. The antimicrobial susceptibility was evaluated by reference broth microdilution methods and the imipenem-resistant isolates were screened for metallo-β-lactamase (MβL) production throughout disc approximation test and MβL Etest® strips and isolates with positive screen test result were submitted to PCR assays using primers bla IMP-1, bla VIM-1, bla VIM-2 e bla SPM-1. The genetic similarity of MβL-producing strains was evaluated by automated ribotyping for epidemiological typing purpose. RESULTS: Resistance rates were high to the majority of antimicrobial agents tested except polymyxin B, which inhibited all samples at the Clinical and Laboratory Standards Institute breakpoint (≤ 2 μg/ml). Twenty-nine (37.2%) isolates were resistant to imipenem and these isolates showed great genomic variability. MβL production was demonstrated in two imipenem-resistant isolates, which were detected using bla SPM-1 and bla IMP-2-specific primers. Sequence analysis revealed the presence of bla SPM-1 and a novel bla IMP-type gene, bla IMP-16. CONCLUSION: The results of this study showed high resistance rates to the majority of antimicrobial agents among P. aeruginosa samples. High imipenem resistance rates were probably due to continuous selection of resistant mutants. The production of MβL did not represent a frequent mechanism of carbapenem resistance in this medical center; but a novel MβL was identified. Continued antimicrobial surveillance and infection control measures should be emphasized to minimize the emergence and dissemination of antimicrobial resistance.