ROLE OF STRUCTURAL AND EXTRACELLULAR VIRULENCE FACTORS IN GRAM-NEGATIVE ANAEROBIC-BACTERIA

Gram-negative anaerobic bacteria belonging to the genera Bacteroides, Prevotella, and Porphyromonas represent the most common cause of endog enous, usually mixed, infections occurring after abdominal or gynecolo gic surgery. Anaerobes are important pathogens in oral-cavity infectio ns as well as in systemic infections that originate from the mouth. Cl inical interest in these organisms is linked to the therapeutic proble ms usually encountered in treating mixed infections. Despite their cli nical relevance, very little is known about the pathogenetic mechanism of anaerobic infections. In Bacteroides species, the capsule has been thought to be important, and initially it was considered unique to Ba cteroides fragilis, the most common pathogen. It has been claimed that the capsule is involved in adhesion, abscess formation, and impaired phagocytosis. However, other structures such as pili and extracellular substances, including metabolic by-products (e.g., short-chain fatty acids), have to be considered as potentially relevant pathogenetic mec hanisms in anaerobic infections. Several extracellular enzymes have be en investigated, but no clear evidence is available for establishing t heir relevance in disease mechanisms. Special attention should be devo ted to enzymes able to digest IgA (IgA proteases), a first-line defens e mechanism that is active in the mucosal membranes.