Snapshot A 25-year-old man presents to the emergency room for pain in his right lower quadrant. He was found to have perforated appendicitis and was immediately taken to the operating room for emergent laparoscopic appendectomy. Due to the complexity of the case, the operation was converted to an open appendectomy. Post-operatively, he was put on a 7-day course of clindamycin and returned home. Two days later, he returned to the emergency room for diffuse abdominal pain. A computed tomography (CT) of his abdomen shows a fluid collection at the site of the appendix. Introduction Classification Bacteroides fragilis an anaerobic, gram-negative bacillus part of the bacterial flora of the mucous membranes including gastrointestinal tract, mouth, and genitals can cause abscesses at any endogenous site, including central nervous system (CNS), head and neck, abdomen, and pelvis Epidemiology incidence more common in chronic infections risk factors immunocompromised state bad dental hygiene animal bite trauma surgery Pathogenesis susceptible to oxidative damage capsule is antiphagocytic penicillin resistance due to beta-lactamase production Presentation CNS infections brain abscess Head and neck infections dental infection retropharyngeal abscess peritonsillar abscess Aspiration pneumonia Empyema Intra-abdominal infections peritonitis abscess Wound infections Imaging Computed tomography (CT) site involved area (i.e., abdomen) indication evaluate for abscess Studies Labs anaerobic culture Making the diagnosis most cases are diagnosed based on clinical findings, imaging, and laboratory studies Differential Necrotizing fasciitis distinguishing factors often also caused by anaerobic bacteria producing gas infection of fascia and presents with pain out of proportion to exam Treatment Management approach the ultimate choice of antibiotic therapy depends on cultured bacteria and its sensitivity profile antibiotics shown below are commonly used against anaerobes Medical metronidazole indication good activity against anaerobes limited activity against aerobic bacteria clindamycin indication B. fragilis is becoming increasingly resistant activity against aerobic, gram-positive cocci as well Operative surgical incision and drainage of abscesses indication abscess Complications Death Contiguous spread of infection