High-level gentamicin-resistant isolates of oral streptococci and Aerococcus from blood specimens

Seventy-nine isolates of oral streptococci and Aerococcus obtained from blood specimens between December 1997 and January 2000 were tested for high-level gentamicin resistance. Three isolates with minimum inhibitory concentrations (MICs) of ≧1024 μg/ml were selected as potential high-level gentamicin-resistant isolates. The DNA sequence of the structural gene encoding 6′-acetyltransferase-2″-phosphotransferase in the three high-level gentamicin-resistant isolates was investigated according to the method used for Enterococcus faecalis . The results of this gene analysis showed that all the DNA sequence of Aerococcus viridans no. 70, which had the highest MIC (2048 μg/ml), matched that of E. faecalis , whereas no polymerase chain reaction (PCR) products were obtained in the other two isolates that were tested. The mechanism of gentamicin resistance in these two isolates is unknown.