Antibacterial activity of various antibiotics against oral streptococci isolated in the oral cavity.

A total of 550 oral streptococci: 270 Streptococcus mitis, 110 Streptococcus sanguis, 90 Streptococcus anginosus, 50 Streptococcus mutans, 30 Streptococcus salivarius, were isolated from dental plaque and gengival crevices of patients and tested for their susceptibility to 12 beta-lactam antibiotics and to 5 non-beta-lactam antibiotics, using the microdiluition method. Overall, a reduced susceptibility to penicillin was recorded in 13.4 percent of cases. The percentage of strains resistant to penicillin appeared significantly higher in S. mitis (24 percent) than in S. sanguis (19 percent), in S. mutans (14 percent) and in S. salivarius (10 percent). No levels of penicillin resistance were shown by 90 strains of S. anginosus. In susceptibility test to antibiotics, imipenem was the most active molecule tested, confirming its general good activity against oral streptococci. Also third generation cephalosporins such as ceftriaxone and fourth generation cephalosporins such as cefepime, showed good activity. Chinolones, glycopeptides and rifampicin confirmed a good activity against oral streptococci.