Modern concepts of small intestinal bacterial overgrowth

Purpose of review Small intestinal bacterial overgrowth (SIBO) has been a recognized condition for more than half a century. Early descriptions of SIBO were based on the concept of colonic bacteria “backing up” into the small intestine. This was based on techniques using unprotected aspiration catheters and earlier culture techniques. Recent advances in breath testing, small bowel sampling, culture techniques, and next generation sequencing have helped expand our understanding of SIBO. Recent findings “SIBO” is now understood to encompass at least three different types of overgrowth including SIBO, intestinal methanogen overgrowth (IMO) and intestinal sulfide overproduction (ISO). Each has their own unique microbial profile. In addition, next generation sequencing has revealed that SIBO is not a migration of colonic flora into the small intestine, but rather overgrowth of two predominant species/strains from phylum Proteobacteria ( Escherichia coli and Klebsiella ). Lastly, results from next generation sequencing of the stool and small intestinal microbiomes have validated breath testing as a diagnostic tool. Summary Together, these advances have allowed the identification of key microbes in overgrowth syndromes, uncovering their relationships to conditions such as irritable bowel syndrome, and paving the way for the development of novel customized treatment options in the future.