The consequences of suppression of anaerobic bacteria.

Anaerobic bacteria such as Bacteroides fragilis, Peptostreptococcus species, and Fusobacterium species, when accompanied by aerobic bacteria or in the presence of dead tissue, can cause severe infections. This article discusses the most common type of anaerobic infection, i.e., infection after colonic contamination of the abdominal cavity and soft tissues. Colonic anaerobes rarely cause infections as solitary pathogens. Mixed infections of aerobes and anaerobes are treated by source control, surgical drainage and debridement, and combination antibiotic therapy. Antimicrobial treatment should cover both anaerobes and aerobes; treatment of mixed infections with anti-anaerobic agents alone is likely to result in abscess formation. Recent trends toward cost cutting and the advent of antibiotics with good coverage of both aerobes and relevant pathogenic anaerobes have led to increased single-agent therapy with cefoxitin, cefotetan, ampicillin/sulbactam, imipenem/cilastatin, ticarcillin/clavulanate, trovafloxacin/alatrofloxacin, and piperacillin/tazobactam. In the past 15 years, research has begun to focus on the gut barrier, particularly on the beneficial effects of anaerobic microflora. Directing antibiotic therapy against the anaerobe when it is involved in clinical infection is important; however, the negative consequences of anti-anaerobic antibiotic therapy on the beneficial effects of normal distal gut colonization must also be considered.