Intraperitoneal Abscesses Abscess formation is common in untreated peritonitis if overt gramnegative sepsis either does not develop or develops but is not fatal. In experimental models of abscess formation, mixed aerobic and anaerobic organisms have been implanted intraperitoneally. Without therapy directed at anaerobes, animals develop intraabdominal abscesses. As in humans, these experimental abscesses may stud the peritoneal cavity, lie within the omentum or mesentery, or even develop on the surface of or within viscera such as the liver. Pathogenesis and Immunity There is often disagreement about whether an abscess represents a disease state or a host response. . | Chapter 121. Intraabdominal Infections and Abscesses Part 5 Intraperitoneal Abscesses Abscess formation is common in untreated peritonitis if overt gramnegative sepsis either does not develop or develops but is not fatal. In experimental models of abscess formation mixed aerobic and anaerobic organisms have been implanted intraperitoneally. Without therapy directed at anaerobes animals develop intraabdominal abscesses. As in humans these experimental abscesses may stud the peritoneal cavity lie within the omentum or mesentery or even develop on the surface of or within viscera such as the liver. Pathogenesis and Immunity There is often disagreement about whether an abscess represents a disease state or a host response. In a sense it represents both while an abscess is an infection in which viable infecting organisms and PMNs are contained in a fibrous capsule it is also a process by which the host confines microbes to a limited space thereby preventing further spread of infection. In any event abscesses do cause significant symptoms and patients with abscesses can be quite ill. Experimental work has helped to define both the host cells and the bacterial virulence factors responsible most notably in the case of B. fragilis. This organism although accounting for only of the normal colonic flora is the anaerobe most frequently isolated from intraabdominal infections is especially prominent in abscesses and is the most common anaerobic bloodstream isolate. On clinical grounds therefore B. fragilis appears to be uniquely virulent. Moreover B. fragilis acts alone to cause abscesses in animal models of intraabdominal infection whereas most other Bacteroides species must act synergistically with a facultative organism to induce abscess formation. Of the several virulence factors identified in B. fragilis one is critical the capsular polysaccharide complex CPC found on the bacterial surface. The CPC comprises at least eight distinct surface polysaccharides. Structural .
