The bactericidal activity of vancomycin and teicoplanin against Streptococcus pneumoniae

The in vitro inhibitory and bactericidal activity of vancomycin and teicoplanin against clinical isolates of Streptococcus pneumoniae was investigated. Minimum inhibitory concentrations (MICs) were determined using an agar incorporation technique. Vancomycin (MIC range 0.12-0.25 mg/l) and teicoplanin (MIC range 0.03-0.12 mg/l) were both very active against the isolates examined. Single-time-point minimum bactericidal concentrations (MBCs) were determined using a macrobroth incorporation technique. Both antimicrobials brought about a 99.9% reduction in viability of the original inocula during 24 hours' exposure at concentrations of 4-8 times the MIC for vancomycin and 2-4 times the MIC for teicoplanin. Time-kill curves of vancomycin, teicoplanin and penicillin against a penicillin-susceptible and a penicillin-resistant strain of S. pneumoniae showed a greater than 3.0 log10 cfu/ml reduction in viability of cultures within 6 hours of exposure to all three of the antimicrobials at a concentration equal to eight times the MIC. The results suggest that clinical trials of the efficacy of teicoplanin in the treatment of infections caused by S. pneumoniae are warranted.