In vivo efficacies of quinolones and clindamycin for treatment of infections with Bacteroides fragilis and/or Escherichia coli in mice: correlation with in vitro susceptibilities.

Therapy with ofloxacin, ciprofloxacin, and lomefloxacin (alone or in combination with clindamycin) and therapy with sparfloxacin, clinafloxacin, and temafloxacin alone were given to mice with subcutaneous abscesses. The abscesses were caused by two Bacteroides fragilis isolates, one of which was susceptible and one of which was resistant to ofloxacin, ciprofloxacin, and lomefloxacin, alone or in combination with Escherichia coli. The abscesses were examined 5 days after inoculation. Numbers of B. fragilis organisms reached log10 10.2 to 11.8 per abscess, and numbers of E. coli organisms reached log10 10.6 to 11.8 per abscess. All of the quinolones reduced the number of susceptible B. fragilis isolates (log10 3.6 to 6.9) and E. coli isolates (log10 5.7 to 6.8). However, ciprofloxacin and lomefloxacin failed to reduce the number of resistant B. fragilis organisms in single-organism or mixed infections. The addition of clindamycin to either ofloxacin, ciprofloxacin, or lomefloxacin reduced the numbers of both susceptible and resistant B. fragilis organisms (log10 3.8 to 7.8). In contrast, sparfloxacin, clinafloxacin, and temafloxacin were effective as single therapy in eradicating B. fragilis resistant to ofloxacin, ciprofloxacin, and lomefloxacin. These in vivo data confirm the in vitro activity of these quinolones and suggest that although ofloxacin, ciprofloxacin, and lomefloxacin are occasionally effective as single agents in eradicating mixed infection by susceptible strains of B. fragilis and E. coli, addition of an agent with activity against anaerobic organisms will ensure their efficacy. Quinolones with good efficacy against B. fragilis may be effective as single-agent therapy of mixed infections.