From the Guidelines
The bacteria most commonly associated with diverticulitis are those from the normal colonic flora, primarily gram-negative anaerobes and facultative gram-negative rods, including Bacteroides fragilis, Escherichia coli, Peptostreptococcus species, Clostridium species, Klebsiella pneumoniae, Streptococcus species, Enterobacter species, and Enterococcus species 1. These bacteria typically exist in a polymicrobial mixture rather than as single pathogens. When diverticula become inflamed or perforated, these normal gut bacteria can invade the weakened intestinal wall, causing infection.
Key Bacteria Involved
- Bacteroides fragilis: the predominant anaerobic organism involved
- Escherichia coli: the most common aerobic bacterium
- Other frequently isolated bacteria: Peptostreptococcus species, Clostridium species, Klebsiella pneumoniae, Streptococcus species, Enterobacter species, and Enterococcus species This is why antibiotic therapy for diverticulitis often includes coverage for both anaerobic and gram-negative organisms, such as combinations of metronidazole with a fluoroquinolone or a third-generation cephalosporin, or single agents like amoxicillin-clavulanate 1. Understanding the bacterial profile of diverticulitis helps explain why broad-spectrum antibiotic coverage is typically necessary when treating this condition.
Treatment Considerations
- Antibiotic treatment can be used selectively, rather than routinely, in immunocompetent patients with mild acute uncomplicated diverticulitis 1
- Antibiotic treatment is strongly advised in immunocompromised patients
- Patients should be educated on the risk of complicated diverticulitis and the importance of personalized management strategies 1
From the Research
Bacteria Associated with Diverticulitis
The bacteria commonly associated with diverticulitis include:
- Facultative and obligate anaerobic gram-negative bacilli 2
- Sulfur-reducing and sulfur-oxidizing bacteria, which are more abundant in complicated diverticulitis 3
- Escherichia coli and Streptococcus spp., which are the predominant aerobic and facultative bacteria in abdominal infections associated with diverticulitis 4
- Bacteroides spp. (B. fragilis group), Peptostreptococcus, Clostridium, and Fusobacterium spp., which are the most frequently isolated anaerobes in abdominal infections associated with diverticulitis 4
Antibiotic Treatment
Antibiotics used to treat diverticulitis include:
- Ampicillin, gentamicin, metronidazole, piperacillin, and tazobactam for severe and complicated diverticulitis 5
- Ciprofloxacin, metronidazole, and rifaximin for uncomplicated diverticular disease 5
- Amoxicillin-clavulanate, which may reduce the risk of fluoroquinolone-related harms without adversely affecting diverticulitis-specific outcomes 6
Microbiome Imbalance
The microbiome of complicated diverticulitis is marked by a localized imbalance of sulfur-metabolizing microbes, with an increased abundance of sulfur-reducing and sulfur-oxidizing bacteria 3