Direct and indirect pathogenicity of anaerobic bacteria in respiratory tract infections in children.

Bacteroides sp (Bacteroides melaninogenicus, Bacteroides oralis, and Bacteroides fragilis), peptostreptococci, and fusobacteria are important pathogens in respiratory tract infections (RTI). These organisms are often recovered mixed with other aerobic, facultative, and anaerobic bacteria. Evidence supporting their virulence is provided by studies showing their synergistic potentials in mixed infections and their increased virulence when encapsulated. A recent increase in numbers of beta-lactamase producing strains of anaerobic gram-negative bacteria in RTI has been associated with increased failure rates of penicillins in eradication of these infections. These infections include chronic otitis media, chronic sinusitis and mastoiditis, chronic recurrent tonsillitis, and lung abscesses. The pathogenicity of these organisms is apparent through their ability not only to survive penicillin therapy but also to protect penicillin susceptible pathogens from that drug. These direct and indirect virulence characteristics of anaerobic bacteria require the administration of appropriate antimicrobial therapy directed against all pathogens in mixed infections. The synergy that exists between different aerobic and anaerobic organisms in the respiratory tract is due to several pathogenic mechanisms. These mechanisms include the production of a capsule, which protects organisms from phagocytosis, and the production of beta-lactamase, which inactivates penicillins and first-generation cephalosporins. Both of these mechanisms enhance infection and induce complications. However, more work is necessary to prevent encapsulation and the production of enzymes. Data, thus far, indicate that there are therapeutic modalities that can be used to prevent these occurrences and eliminate many mixed RTI.