In-vitro activity of synercid and related drugs against Streptococcus oralis isolated from septicaemia and endocarditis cases

Objective-The increase in resistance to gram positive organisms and seriousness of infective endocarditis, makes it necessary to look for an alternate treatment. Method-In-vitro activity of synercid was compared with penicillin, amoxycillin, teicoplanin, vancomycin, clindamycin and erythromycin. Result-Synercid showed minimum inhibitory concentrations (MIC) within the narrow range of 0.06-0.5 mg/l. MIC₅₀ and mode values were both 0.25 mg/l. There was just two-fold difference between the MIC₅₀ (0.25 mg/l) and the MIC₉₀, (0.5 mg/l). Although the MICs of synercid for S. oralis were relatively high compared to penicillin, clindamycin, erythromycin and teicoplanin, the in-vitro bactericidal activity of synercid was much greater. Synercid MBC values were < 4 mg/l for most of the isolates, except for one of 16 mg/l and the other >64 mg/l. Killing curve was performed on six isolates of S. oralis from infective endocarditis, two from septicaemia patients and two from the oral flora of normal individuals. Conclusion-Synercid showed superior bactericidal activity when compared to penicillin and vancomycin against all ten isolates of S. oralis tested. Synercid was bactericidal (99.9% kill) against all ten isolates of S. oralis within six hours of contact.