A preliminary study of the upper bowel microbiota in patients with SIBO

Small intestinal bacterial overgrowth (SIBO) is a heterogeneous syndrome characterized by an increased number of bacteria in the small bowel. SIBO is diagnosed when bacterial cultures of upper intestine aspirates are ¿105 CFU/ml. Although investigation of these aspirates is considered the gold standard, non-invasive hydrogen breath test are commonly used for SIBO diagnosis. This syndrome has been related with a decrease of small bowel motility, an increase of intestinal permeability and bacterial translocation, being associated with serious diseases such as liver cirrhosis. To investigate the alterations in the bacterial communities of the small bowel from SIBO patients and the potential link with microbiota from other sites (saliva and feces). Duodenal aspirates from patients diagnosed with SIBO, control subjects and cirrhotic patients, with and without SIBO, were used to determine bacterial load (by quantitative PCR) and composition (by Illumina sequencing of 16S rDNA amplicons). Saliva and feces from cirrhotic patients were also included for comparative purposes. Bacterial quantification by qPCR revealed counts higher than 5 x 106 genome equivalents/ml of duodenal aspirates in SIBO patients whereas in the control subjects were below 106. Bacterial composition was represented by members of the Lactobacillales order, diverse families of protebacteria and genera belonging to Prevotellaceae, Veillonellaceae and Micrococcaceae families. No statistical differences were seen between the taxons presented in SIBO and non-SIBO cirrhotic patients. A further investigation with a broad number of patients is needed to confirm whether: i) the usual methods employed for SIBO diagnosis are reliable, and ii) the microbiota of duodenal aspirates in cirrhosis is more closely related to that of the oral cavity than the distal gut.