A 67-year-old male presents with an intraabdominal abscess secondary to perforated sigmoid diverticulitis. The following statement(s) is/are true concerning his intraabdominal abscess

b. Both aerobic and anaerobic islets are encountered in 50% of specimens

c. The most common aerobic islet will be likely E. coli and other gram-negative enteric bacilli

d. The most common anaerobic islet will be a Bacteroides species

Typically an intraabdominal infection results in perforation of a hollow viscus and the ensuing contamination of a normally sterile peritoneal cavity. The normal bacterial flora found in that particular location of the alimentary tract thus determines the initial inoculum. In parallel with the overall quantity of microorganisms, (both aerobes but predominantly anaerobes) perforations of the lower small bowel and colon produce a high frequency of infections that contain anaerobic microorganisms. Certain predictable patterns of bacterial islets are found, but on average four to five islets occur in patients with established intraabdominal infection, more than half of which are anaerobes. Both aerobes and anaerobes are encountered in 80% to 90% of specimens. Commonly encountered aerobes isolated are E. coli and other gram-negative enteric bacilli such as Enterobacter, Klebsiella. Among the anaerobes, Bacteroides species (especially B. fragilis, Clostridium), and anaerobic cocci are most consistently isolated.