Is Klebsiella aerogenes Normal in Stool?
Yes, Klebsiella aerogenes (formerly Enterobacter aerogenes) can be present in stool as part of the normal intestinal flora and does not necessarily indicate disease. 1
Understanding K. aerogenes in the Gastrointestinal Tract
- K. aerogenes is a Gram-negative bacterium that is ubiquitously present in all environments including water, soil, air, and the human gastrointestinal tract 2
- This organism is part of the Enterobacteriaceae family, which normally composes the intestinal flora alongside other aerobes and facultative anaerobes 1
- The presence of K. aerogenes in stool does not automatically indicate pathogenicity or require treatment 1
When K. aerogenes Becomes Clinically Significant
K. aerogenes is an opportunistic pathogen that causes disease primarily in specific clinical contexts, not as a cause of routine gastroenteritis. 2, 3
Clinical scenarios where K. aerogenes matters:
- Nosocomial infections: Hospital-acquired infections including urinary tract infections, surgical site infections, and catheter-related bloodstream infections 4, 3, 5
- Bacteremia: Bloodstream infections in hospitalized patients with invasive devices or significant comorbidities, with mortality rates around 20% 5
- Immunocompromised hosts: Patients with weakened immune systems are at higher risk for invasive infections 2, 3
K. aerogenes is NOT a routine cause of gastroenteritis:
- Standard stool culture protocols for infectious diarrhea target Salmonella, Shigella, Campylobacter, and Shiga toxin-producing E. coli—not K. aerogenes 1
- The detection rate of K. pneumoniae (a closely related species) in stool from outpatients with diarrhea syndromes was only 0.5%, suggesting Klebsiella species are uncommon diarrheal pathogens 6
- Guidelines for bacterial gastroenteritis do not list K. aerogenes as a pathogen requiring specific testing or treatment 1, 7
Important Clinical Distinctions
- Colonization vs. infection: Finding K. aerogenes in stool typically represents colonization, not infection, unless there are systemic signs of illness (fever, sepsis, severe abdominal pain) 7
- Context matters: If K. aerogenes is isolated from stool in a patient with diarrhea, consider alternative explanations for the diarrhea and look for other pathogens 1, 7
- Fecal indicator interpretation: While E. coli is a specific fecal indicator, Klebsiella species (including K. aerogenes) can be found in both fecal and non-fecal environmental sources 1
When to Be Concerned
Order blood cultures and consider invasive infection if:
- Patient has fever, signs of sepsis, or systemic illness beyond simple gastroenteritis 7, 5
- Patient is hospitalized with invasive devices (catheters, surgical drains) 3, 5
- Patient is immunocompromised or has significant comorbidities 5
- There is concern for bacteremia or deep tissue infection rather than simple gastroenteritis 7, 5
Antibiotic Resistance Considerations
- Community-acquired K. aerogenes strains generally show lower resistance rates compared to hospital-acquired strains 6
- Multidrug resistance and ESBL production occur in approximately 5-6% of cases, primarily in nosocomial settings 5
- All K. aerogenes strains show universal resistance to amoxicillin-clavulanate, with 73% resistance to ampicillin 6