Molecular identification of aminoglycoside-modifying enzymes among strains of Enterococcus spp. isolated in hospitals of the VIII region of Chile

Background: Infectious diseases produced by Enterococcus spp, must be treated with a synergistic combination between a penicillin and an aminoglycoside. High level resistance to aminoglycosides is a serious therapeutic problem, since it predicts the loss of synergistic activity of this antimicrobial combination. Aim: To investigate the presence of genes encoding aminoglycoside-modifying enzymes (AMEs) among stains of Enterococcus spp with high level of resistance to aminoglycosides. Material and methods: The genes encoding some of the AMEs were investigated among 305 aminoglycoside-resistant stains of Enterococcus spp isolated in hospitals of the VIII region of Chile, by dot blot hybridization and Polymerase Chain Reaction (PCR). Results. High level resistance to some aminoglycosides was observed in 104 strains (34.1%) and 93 of these harbored at least one of the genes encoding the investigated AMEs. Three genes were detected: aac(6')Ie-aph(2 '')Ia (14.8%) encoding for the enzyme AAC(6')Ie-APH(2')la (resistance to all aminoglycosides, except streptomycin); aph(3')IIIa (26%), and ant(6')Ia (28.5%) encoding for the phosphorylating enzymes APH(3')IIIa (resistance to kanamycin, amikacin and neomycin), and ANT(6')-Ia (resistance only to streptomycin), respectively. None of the strains harbored the gene ant (4) which encode for the enzyme ANT (4'). Conclusion: The low frequency of strains harbouring the bifunctional enzyme (< 15%), conferring an extended resistance profile to aminoglycosides, allows us to propose the empirical use of aminoglycoside-aminocyclitols, associated to a penicillin, in the treatment of serious infections produced by species of enterococci (Rev Med Chile 2007, 135: 566-72).