[In vitro activity of penicillin G and amoxicillin against 14 strains of Streptococcus milleri].

The MIC/MBC of penicillin G and amoxicillin were studied for 14 strains of Streptococcus milleri from varied specimens of hospitalized patients by broth dilution method. The MIC of penicillin G are between 0.015 and 0.12 mg/l, MIC of amoxicillin between 0.015 and 0.5 mg/l. The MBC of penicillin G are between 0.015 and 0.12 mg/l, MBC of amoxicillin between 0.12 and 0.5 mg/l. MBC/MIC of penicillin G are between 1 and 8. MBC/MIC of amoxicillin are between 1 and 16. The bactericidal effect was studied by killing curves on 5 strains at 2, 4, 6 and 18 hours at different concentrations of penicillin G (0.1, 0.2, 1 mg/l) and of amoxicillin (0.2, 0.5, 1 mg/l). For 3 strains we observed a bactericidal effect with 99.9% or 99.99% of killing between the 6th and 18th hour without difference between penicillin G and amoxicillin, the two further strains were killed respectively by 0.1 mg/l of penicillin G and 0.5 mg/l of amoxicillin and by 0.2 mg/l of penicillin G and 0.5 mg/l of amoxicillin.