High Prevalence of the Gene in Hospital Isolates of Co-Resistant to Gentamicin and Penicillin.

This study aimed to characterize the molecular mechanism of resistance to gentamicin among penicillin-resistant, ampicillin-susceptible (PRASEF) isolates by investigating the presence of the gene. The co-resistance to antimicrobials of other classes was also evaluated. Among the 151 isolates evaluated, 70 were PRASEF and 81 were penicillin-susceptible and ampicillin-susceptible (PSASEF). No β-lactamase producing isolate was detected. Eighty-three (55.0%) and 35 (23.2%) out of the 151 isolates showed high-level gentamicin resistance (HLGR) and high-level streptomycin resistance (HLSR) phenotypes. However, a significantly higher rate of PRASEF (88.6%) showed HLGR phenotype in comparison with PSASEF (23.5%) ( < 0.01). Conversely, a significantly lower rate of PRASEF (14.3%) showing HLSR was observed in comparison with PSASEF (30.9%) ( = 0.02). The prevalence of isolates displaying multidrug resistance (MDR) phenotype was significantly higher ( < 0.01) in the group of PRASEF (81.4%) than in PSASEF (18.6%). The majority of PSASEF (61.9%) and PRASEF (90.3%) isolates showing HLGR phenotype was harboring the gene, which encodes a bifunctional enzyme that inactivates all aminoglycosides except streptomycin. The gene was prevalent among the Brazilian PRASEF isolates that usually exhibit co-resistance to gentamicin and to multiple other drugs.