From the Guidelines
The four physiologic protective mechanisms that prevent Small Intestinal Bacterial Overgrowth (SIBO) are gastric acid secretion, intestinal motility, the ileocecal valve, and antimicrobial peptides. These mechanisms work together to maintain a healthy balance of bacteria in the small intestine and prevent the overgrowth of harmful bacteria. Gastric acid secretion creates an acidic environment in the stomach that kills many ingested bacteria before they can reach the small intestine 1. Intestinal motility, particularly the migrating motor complex (MMC) that occurs between meals, acts as a "housekeeping wave" that sweeps residual food and bacteria toward the colon, preventing bacterial accumulation in the small intestine. The ileocecal valve serves as a mechanical barrier between the bacteria-rich colon and the relatively sterile small intestine, preventing backflow of colonic contents. Finally, antimicrobial peptides secreted by Paneth cells in the small intestine help maintain the normal bacterial balance by selectively killing certain microorganisms. Dysfunction in any of these mechanisms can lead to SIBO, which is characterized by excessive bacterial growth in the small intestine, potentially causing symptoms like bloating, diarrhea, malabsorption, and nutrient deficiencies. Some key points to consider in the management of SIBO include the use of rotating antibiotics, as recommended by recent guidelines 1. However, the primary focus should always be on maintaining the health and function of the physiologic protective mechanisms to prevent SIBO from occurring in the first place. Key factors to consider include:
- Gastric acid secretion: essential for killing ingested bacteria
- Intestinal motility: critical for sweeping residual food and bacteria toward the colon
- Ileocecal valve: acts as a mechanical barrier between the colon and small intestine
- Antimicrobial peptides: help maintain the normal bacterial balance in the small intestine.
From the Research
Physiologic Protective Mechanisms
The following are four physiologic protective mechanisms that prevent SIBO:
- Gastric acid secretion: This mechanism helps to reduce the number of bacteria that enter the small intestine 2.
- Intestinal motility: The movement of the intestines helps to prevent the overgrowth of bacteria in the small intestine 2, 3.
- Intact ileo-caecal valve: This valve helps to prevent the backflow of bacteria from the large intestine into the small intestine 2, 3.
- Immunoglobulins within intestinal secretion and bacteriostatic properties of pancreatic and biliary secretion: These mechanisms help to prevent the overgrowth of bacteria in the small intestine by providing an immune response and inhibiting the growth of bacteria 2.