Interference of antibiotics in the growth curves of oral streptococci

The growth curve interference (GCI) induced by different antibiotics was studied using reference strains of oral streptococci. This parameter may prove to be useful in preventing subacute endocarditis of odontological origin in high-risk patients. The growth curves using different concentrations of antibiotics and with an initial optical density (OD) of 0.05 ± 0.01 were observed until an OD of 0.9–1.0 was reached. The GCI was defined as the lowest concentration of antibiotic that modified the growth curve with respect to a control without antibiotic. The GCI values were then compared with the minimum inhibitory concentration (MIC) values. In all cases, interference in the growth curves was at least one concentration lower than the MIC in a time ranging from 4–6 h.