In vitro activity of rifaximin and rifampicin against some anaerobic bacteria.

Activity of rifampicin and of a new rifamycin, rifaximin, was tested in strains of anaerobic bacteria belonging to the Bacteroides genus (75 B. fragilis group and 17 Bacteroides non-fragilis group) and in Clostridium perfringens (15 strains). It turned out that the bactericidal activity of both rifamycins could be overlapped and that it equalled 100% in the case of the non-fragilis Bacteroides and Clostridium species.