Aminoglycoside-modifying enzymes in high-level streptomycin and gentamicin resistant Enterococcus spp. in Spain

Aminoglycoside resistance was evaluated in 690 enterococcus strains isolated from different clinical sources originating from patients at the University Clinic Hospital of Zaragoza (Spain). The enterococci obtained from clinically significant samples (blood, urine, or exudates) showed more high-level resistance to gentamicin and streptomycin (65 and 42%, respectively) than those isolated from faecal samples (49 and 23%, respectively). Aminoglycoside-modifying enzymes (AME) from 119 of these high-level gentamicin and streptomycin resistant enterococcus strains were studied. The most frequent AMEs found were APH(3′) and AAC(6′)-APH(2″). More than one enzyme was detected in 71% of the strains (four different enzymes in 5% of the strains). Three Enterococcus faecalis strains had ANT(4′)(4″) enzymatic activity. Different enzymatic expressions of the bifunctional enzyme AAC(6′)-APH(2″) were demonstrated in strains in which the complete aac(6′)-aph(2″ ) gene was detected by PCR and hybridization: (i) AAC(6′)+APH(2″) activity; (ii) AAC(6′) only; (iii) APH(2″) only; and (iv) no activity of AAC(6′) or APH(2″).