SIBO is a condition in which the small intestine becomes colonized with abnormally high counts of aerobic and anaerobic bacteria normally found in the colon. Bacteria commonly associated with SIBO include Escherichia coli as well as those from the genuses Lactobacillus, Bacteroides, and Streptococcus.
The etiology of SIBO involves diminished intestinal motility and altered mucosal defenses. With reduced GI motility, the small bowel can’t get cleared of debris efficiently. Colonic microbes grab a foothold and bloom. Conditions marked by diminished intestinal motility – and high rates of SIBO – include scleroderma, diabetes, irritable bowel syndrome, chronic pancreatitis, cirrhosis, common variable immunodeficiency, HIV infection, and radiation enteritis. Small bowel diverticula are a setup for SIBO. Long-term proton pump inhibitor–therapy fosters hypochlorydia, which promotes SIBO. Opioid therapy is another common cause of SIBO.
So is bariatric surgery. “Bariatric surgery has caused so much iatrogenic GI disease, it’s just amazing. There is bacterial overgrowth in that population, and it’s a lot more complex than basic SIBO,” Dr. Mahadevan said.
SIBO causes malabsorption across the intestinal microvillus membrane as a result of damage to enterocytes, as well as impaired digestion in the intestinal lumen.