In complicated diverticulitis with abscess or perforation, antibiotic therapy should cover which organisms?

• A. Gram-positives only
• B. Gram-negatives and anaerobes
• C. Atypical bacteria only
• D. Fungi

Answer: (B)

Complicated diverticulitis with abscess or perforation is usually a polymicrobial infection coming from the gut. The colon harbors both anaerobic bacteria (especially Bacteroides fragilis group) and Gram-negative facultative bacilli (like E. coli, Klebsiella). Because the infection is driven by this mix of organisms, empirical antibiotic therapy must include coverage for both anaerobes and Gram-negative bacteria to effectively control the infection and prevent spread. Atypical bacteria and fungi are not the primary pathogens in this scenario, so they are not the focus of standard empiric therapy unless specific risk factors or clinical clues suggest them. In practice, regimens that target both groups are used upfront, with de-escalation once cultures identify the exact pathogens.