CHROMOSOMALLY MEDIATED HIGH-LEVEL GENTAMICIN RESISTANCE IN STREPTOCOCCUS-MITIS

Four blood culture isolates of Streptococcus mitis were found to be re sistant to penicillin (MIC, 16 to 32 mu g/ml) and gentamicin (MIC, 128 or 1,000 mu g/ml), and the two antibiotics demonstrated a lack of in vitro synergy. As shown by polymerase chain reaction assays, the struc tural gene known to encode high-level gentamicin resistance in Enteroc occus faecalis, Enterococcus faecium, and Streptococcus agalactiae was also present in all four S. mitis strains. Attempts to isolate plasmi ds were unsuccessful, but an oligonucleotide probe derived from the ge ntamicin resistance gene hybridized to distinct restriction fragments of genomic DNA, suggesting that the resistance genes in these strains are integrated into the bacterial chromosome.