Pathogenicity of Clostridium species with other bacteria in mixed infections.

The relationship of clostridial isolates with other bacteria in mixed infections was studied by means of a subcutaneous abscess model in mice. We used 26 isolates of seven clostridial species, two Bacteroides spp., eight Gram-positive facultative or anaerobic cocci and three enteric Gram-negative aerobic rods. Abscesses were induced by all seven Clostridium perfringens and three C. butyricum isolates and by some of the others. Selective antimicrobial therapy experiments showed that enteric Gram-negative rods were of equal or greater significance in the formation of abscesses than were clostridial strains in mixed infections. Enhancement or suppression of each component of the mixed infection was studied by comparing the number of each bacterium to its number when injected alone. Enhancement was observed mainly with C. perfringens in mixed infections. By contrast, other Clostridium spp. were less able to induce enhancement. Clostridium difficile and C. sporogenes often inhibited other bacterial species. This study demonstrated the synergistic and antagonistic relationship between clostridial species and other bacteria.