Background: Benzathine penicillin G every 3 weeks is the standard protocol for secondary prophylaxis for recurrent rheumatic fever.
Objective: Assess the effect of Benzathine penicillin G on Streptococcus sanguinis and Streptococcus oralis in patients with cardiac valvular disease due to rheumatic fever receiving secondary prophylaxis.
Methods: Oral streptococci were evaluated before (baseline) and after 7 days (day 7) with Benzathine penicillin G in 100 patients receiving routine secondary rheumatic fever prophylaxis. Saliva samples were evaluated for colony count and presence of S. sanguinis and S. oralis. Chewing-stimulated saliva samples were serially diluted and plated onto both nonselective and selective 5% sheep blood agar containing penicillin G. The species were identified using conventional biochemical tests. Minimal inhibitory concentrations were determined with the Etest.
Results: No statistical differences were found in the presence of S. sanguinis comparing baseline and day 7 (p = 0.62). However, the existing number of positive cultures of S. oralis on day 7 after Benzathine penicillin G presented a significant increase compared to baseline (p = 0.04). No statistical difference was found between baseline and day 7 concerning the number of S. sanguinis or S. oralis CFU/mL and median minimal inhibitory concentrations.
Conclusion: This study showed that Benzathine penicillin G every 3 weeks did not change the colonization by S. sanguinis, but increased colonization of S. oralis on day 7 of administration. Therefore, susceptibility of Streptococcus sanguinis and Streptococcus oralis to penicillin G was not modified during the penicillin G routine secondary rheumatic fever prophylaxis.