Critical Review: The Past, Present, and Future of Small Intestinal Bacterial Overgrowth (SIBO)

Small intestinal bacterial overgrowth (SIBO) has evolved from a severe debilitating illness to a clinical spectrum associated with abnormalities of microbial populations in the small intestine. It is best described as a pathophysiological state that may contribute to symptoms or other pathology in a wide range of gastrointestinal conditions that include disorders of gut-brain interaction, inflammatory bowel disease, and chronic liver disease. The controversy surrounding SIBO largely rests on diagnostic limitations of currently widely used diagnostic tests. The gold standard test of bacterial culture of proximal small intestinal fluid will miss the majority of bacteria, has severe methodological limitations, and is clinically uncommonly used. Breath-hydrogen testing after oral glucose or lactulose ingestion is associated with falsely positive and negative results, due largely to the inability to accurately define where in the gastrointestinal tract the hydrogen is being generated. Such performance characteristics raise concerns regarding its application to clinical decision-making in the individual patient. Therapies such as antibiotics can normalize breath test findings and ameliorate symptoms, but whether this is due to an action on the small intestinal microbiota is uncertain. It is proposed that conceptual modifications that include the assessment of the mucosa-associated microbiota in biopsies obtained with minimal contamination, molecular and functional characterization of the microbiota, rather than purely culture-based density of bacteria, and expansion of the definition of SIBO to small intestinal dysbiosis will facilitate more precision and resolve the controversial place of SIBO in clinical practice.