In-vitro antimicrobial susceptibility of the "Streptococcus milleri' group (Streptococcus anginosus, Streptococcus constellatus and Streptococcus intermedius).

A collection of 423 clinical "Streptococcus milleri' strains was speciated and tested for susceptibilities to twelve antibiotics. Only 1.4% of the strains were of intermediate susceptibility to penicillin. None of the strains exhibited high-level resistance to gentamicin. Strains resistant to erythromycin, roxithromycin and clindamycin were found with a frequency of 2.6%, 2.4% and 2.4% respectively. Doxycycline resistance was found in 5.7% of the strains and occurred most frequently in Streptococcus anginosus. All the strains were susceptible to cefotaxime, vancomycin and teicoplanin. The results of this study do not indicate changing antibiotic resistance in strains of the "S. milleri' group, but local differences in antibiotic susceptibilities may occur.