In vitro activity of vancomycin and teicoplanin against anaerobic bacteria

The in vitro activity of vancomycin and teicoplanin, a new glycopeptide antimicrobial, was determined against a total of 286 anaerobic bacteria including Bacteroides fragilis group (100), B. melaninogenicus (21), B. bivius (16), Fusobacterium spp. (15), Peptococcus spp. (20), Peptostreptococcus spp. (21), Clostridium perfringens (23), C. difficile (41) and Propionibacterium acnes (29). Minimum inhibitory concentrations (MIC) were determined using an antimicrobial incorporation technique in Wilkins-Chalgren agar approximately 10(4) colony forming units (cfu) contained in 10 microliters Wilkins-Chalgren broth, which was applied to the surface of the agar plates using a multipoint inoculator. Following inoculation, plates were incubated for 48 h at 37 degrees C in an anaerobic atmosphere. Both vancomycin and teicoplanin were highly active against all the Gram-positive anaerobic bacteria examined, 90% of all isolates being inhibited by 0.5 micrograms/ml of either antimicrobial. Isolates of B. fragilis group and Fusobacterium spp. were resistant to vancomycin (MIC90 64 micrograms/ml) and teicoplanin (MIC90 128 micrograms/ml). Unexpectedly, isolates of B. melaninogenicus and B. bivius which were resistant to vancomycin (MIC90 64 and 128 micrograms/ml respectively) were sensitive to teicoplanin (MIC90 2 and 2 micrograms/ml respectively).