High-level gentamicin resistance (HLGR) in enterococci eliminates the synergistic bactericidal effect of combined exposure to cell wall-active agent and gentamicin. In such instance, controlling the spread of these organisms becomes of paramount importance.
With the recent emergence of HLGR enterococci, 147 enterococcal urinary tract infection isolates from 7 medical care units in Tehran during 1 year (2005-2006) were collected. Speciation was based on using conventional biochemical tests and confirmed by polymerase chain reaction technique. Antimicrobial susceptibility tests were assayed for 10 antibiotics with the disk diffusion method.
Enterococcus faecalis (70%) and Enterococcus faecium (30%) were the most important species. The results obtained from polymerase chain reaction showed a high rate of agreement with phenotypic assays for both species. High-level gentamicin resistance phenotype was detected in 61.5% of E. faecalis and 79% of E. faecium strains. Susceptibility to different antimicrobial agents between 2 species was different. All HLGR isolates contained the aac(6′)-Ie-aph(2″)-Ia gene. The high prevalence of HLGR enterococcal strains shown by the present study revealed the emergence of effective antibiotic therapy for enterococcal infections that should be based on accurate antimicrobial susceptibility tests and species identification.