A 22-year-old male presents to the emergency department complaining of fever, abdominal pain, and vomiting. He has had these symptoms for the past four days, but has not sought medical attention because of concerns over the cost of treatment. On examination, the patient appears acutely ill. There is right lower quadrant tenderness with rebound as well as a palpable mass. CT scan of the abdomen and pelvis demonstrates a periappendiceal fluid collection. Culture of this fluid would most likely isolate which of the following organisms?
This patient is suffering from perforated appendicitis that has evolved into an intraabdominal abscess. Although most infections within the abdominal cavity are polymicrobial, B. fragilis is a common anaerobic gram-negative bacillus that is frequently isolated, and of the choices given, it is the most likely organism to be identified in the culture of this patient's abscess. This organism expresses unique surface polysaccharides that have been shown to favor abscess formation. In addition to B. fragilis, common bacterial isolates from intraabdominal infections include other members of the normal colonic flora such as Escherichia coli, enterococci, and streptococci.
(Choice A) S. aureus is a gram-positive organism that can cause abscess formation on the skin, but is not typically isolated from an intraabdominal abscess.
(Choice B) Actinomyces species are anaerobic bacteria that can form abscesses in the cervicofacial region or abdominal cavity. However, they are much less common than B. fragilis and typically do not form abscesses this quickly.
(Choice C) Candida albicans can be isolated from an infection resulting from perforation of the proximal bowel such as a perforated peptic ulcer.
(Choice E) Infection with E. histolytica can result in the formation of an amebic liver abscess. This patient, however, has perforated appendicitis, which is not related to infection with E. histolytica.
Educational objective:
Intraabdominal infections are polymicrobial, with B. fragilis and E. coli being the most prominent organisms isolated.