Effect of benzathine penicillin treatment on antibiotic susceptibility of viridans streptococci in oral flora of patients receiving secondary prophylaxis after rheumatic fever

Objective: To assess the level of antibiotic resistance of viridans streptococci in the oral flora of children with a history of rheumatic fever, receiving long-term monthly intramuscular benzathine penicillin G prophylaxis. Patients and methods: Oral swabs from patients receiving monthly penicillin G prophylaxis for rheumatic fever were cultured and tested for viridans streptococci. The E-test was used to test susceptibility to penicillin G, clindamycin, clarithromycin and rifampin. Findings were compared with samples from healthy children who had not been exposed to antibiotic treatment for at least 2 months. Results: Twenty-six patients and 20 control children were included in the study. Duration of intramuscular antibiotic treatment ranged from 5 months to 13.5 years. Sixty isolates of viridans streptococci species were obtained, with a similar distribution in the two groups. Intermediate resistance to penicillin (MIC 0.25-2 mg/L) was documented in 10 of the 32 isolates (31.2%) in the study group, and high resistance in none, compared to seven of 28 isolates (25%) with intermediate or high resistance in the control group (p = NS). All isolates in the study group and all but one in the control group were susceptible to clindamycin, and all isolates from both groups were susceptible to rifampin. One isolate (3.1%) in the study group and two (7.1%) in the control group were resistant to clarithromycin. Conclusion: Monthly Intramuscular penicillin prophylaxis has no effect on the antibiotic susceptibility of viridans streptococci in oral flora in children with a history of rheumatic fever, receiving secondary prophylaxis after rheumatic fever, regardless of the duration of treatment.