Bacterial populations contaminating the upper gut in patients with small intestinal bacterial overgrowth syndrome.

OBJECTIVE: Small intestinal bacterial overgrowth syndrome (SIBOS) is characterized by an abnormally high bacterial population level in the upper gut, exceeding 10(5) organisms/ml (5 log colony-forming unit (CFU)/ml). To understand its origin and select an appropriate antibiotic treatment, we have analyzed the bacterial populations contaminating the upper gut in SIBOS patients.

METHODS: Jejunal samples of 63 consecutive patients with diarrhea or malabsorption and conditions predisposing to SIBOS were cultured and antibiotic sensitivities determined.

RESULTS: Concentrations of total, microaerophilic, and anaerobic bacteria were confirmed in 55 patients with SIBOS (mean +/- SE) 7.6 +/- 0.8, 7.4 +/- 0.9, and 6.1 +/- 0.7 log CFU/ml, respectively. Mean number of bacterial genera was 4.6 +/- 0.8. The main bacteria recovered were (mean +/- SE log CFU/ml) Streptococcus (71%; 6.4 +/- 0.8), Escherichia coli (69%; 7.2 +/- 0.9), Staphylococcus (25%; 6.2 +/- 0.6), Micrococcus (22%; 6.0 +/- 0.7), Klebsiella (20%; 7.1 +/- 0.8), Proteus (11%; 6.1 +/- 0.8) for microaerophilic bacteria, and Lactobacillus (75%; 6.1 +/- 1.1), Bacteroides (29%; 6.9 +/- 1.3), Clostridium (25%; 5.5 +/- 1.0), Veillonella (25%; 5.3 +/- 0.7), Fusobacterium (13%; 4.8 +/- 0.5), and Peptostreptococcus (13%; 6.1 +/- 0.7) for anaerobic bacteria. Amoxicillin-clavulanic acid and cefoxitin were efficient on >90% of strains.

CONCLUSIONS: Contaminating flora isolated in SIBOS include commonly identified oropharyngeal and colonic flora, but these occur in SIBOS at different levels from those usually found in their original location. These data may hopefully serve as a starting point to further therapeutic controlled studies.