Antibiotic-resistant oral streptococci in dental patients susceptible to infective endocarditis.

The aim of this study was to determine the incidence of amoxycillin and erythromycin resistance in oral streptococci in patients at risk from infective endocarditis. Samples of gingival crevicular flora were taken from 65 patients at the site of dental treatment, prior to the prophylactic administration of amoxycillin (54 patients) or erythromycin (11 patients). Samples were also taken from 65 dental patients who were not considered to be at risk from infective endocarditis. No isolate had a minimum inhibitory concentration (MIC) of amoxycillin greater than 24 mg/L. However, erythromycin-resistant oral streptococci with MIC values greater than 3.5 mg/L were isolated from 22% of patients receiving amoxycillin prophylaxis, 9% of patients receiving amoxycillin prophylaxis, 9% of patients given erythromycin prophylaxis and 9% of patients not at risk from infective endocarditis. The antibiotic-resistant streptococci comprised mainly Streptococcus sanguis biotype II, although S. sanguis biotype I, S. mitis and S. salivarius were also frequently recovered.