Entry, Spread and Multiplication
Site of Infection As noted above, the gram negative anaerobes, particularly Bacteroides and Prevotella, make up the normal flora. Thus, the site of infection involving one of these organisms is not usually its niche. Infection associated with Bacteroides as an example, is associated with breakage of the colon wall, and spilling of feces into the peritoneum. This may occur due to inflammation (appendicitis), trauma, rupture, or surgery. For Prevotella, a site of injury or inflammation (trauma, cesarean section, pelvic inflammatory disease) may promote infection by these organisms.
Growth and Spread Following the introduction of Bacteroides and other colonic flora into the new environment (usually the peritoneum), a dynamic host/parasite reaction occurs. On the host side, phagocytes, mesentery, and omentum are all recruited to "wall off" and attempt to eliminate the "invading" organisms. Oxygen will quickly kill oxygen sensitive anaerobes, but facultative anaerobes and Bacteroides will survive. Initially, the facultative organisms will grow, but as the environment becomes reduced, Bacteroides will then be allowed to grow and cause damage.
Bacteroides emerges as a dominant anaerobe in this setting. Its importance may be due to one or more virulence factors.
2O2-+2H+ -----------------> H2O2 + O2
2H2O2 --------------> 2H2O + O2
Adherence - to peritoneal cavity
Resistance to phagocytosis
Resistance to T cell and humoral immunity
Prevotella is not encapsulated