Beta-lactam resistance mechanisms in Pseudomonas aeruginosa strains causing bloodstream infections: comparative results between Brazilian and American isolates.

This study evaluated the presence of distinct mechanisms of beta-lactam resistance in 122 Pseudomonas aeruginosa isolates, causing bloodstream infections at Hospital São Paulo (HSP, Brazil; 82 isolates) and Virginia Commonwealth University Medical Center (VCU, United States; 40 isolates). By Clinical Laboratory Standards Institute agar dilution, Brazilian P. aeruginosa isolates showed higher resistance rates to most antimicrobials tested than those collected from the United States, except for ciprofloxacin. Carbapenem hydrolysis was detected in seven P. aeruginosa from HSP, in which bla(SPM-1) (n=5), bla(IMP-1) (n=1), and bla(IMP-16) (n=1) were detected by polymerase chain reaction (PCR) followed by DNA sequencing. The production of GES-5 was observed in 1.25% of HSP isolates. No extended-spectrum beta-lactamase-encoding genes were detected in the VCU isolates. Expression of efflux systems genes (mexB, mexD, mexF, and mexY) was evaluated by quantitative reverse transcriptase-PCR. In HSP isolates MexXY-OprM (41.4%) efflux system was more frequently overexpressed, in contrast to what was observed in the VCU isolates, where both MexXY-OprM (25.0%) and MexAB-OprM (25.0%) were equally overexpressed. The oprD downregulation was similar among isolates collected from the HSP (92.7%) and VCU (95.0%). On the other hand, ampC overexpression was observed only among HSP isolates (31.7%). The distinct antimicrobial susceptibility profile and mechanisms of beta-lactam resistance found among P. aeruginosa isolated from teaching hospitals located in Brazil and the United States exemplify the importance of local epidemiology in determining antimicrobial resistance rates.