Normal intestinal flora has been implicated in the pathophysiology of inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis. A review published in the Scandinavian Journal of Gastroenterology (2001; 36(Suppl 234):29–40) examined the relationship between bowel flora, intestinal permeability, and immune responses in IBD.
The intestinal tract forms a continuous tube from the mouth to the anus, and its contents are technically external to the body. The epithelial cells lining the intestine serve as a selective barrier, regulating which substances are absorbed and which remain within the lumen. When this barrier function is impaired, increased intestinal permeability—sometimes referred to as increased gut permeability—can occur. The review described evidence suggesting that increased permeability may contribute to a loss of immune tolerance to bacteria that normally inhabit the intestine.
The authors noted that patients with IBD appear to mount an abnormal immune response against components of their own bowel flora. In addition, both the composition and behavior of intestinal bacteria differ in patients with IBD compared with healthy individuals.
Invasive behavior of intestinal bacteria has also been documented. Research published in Gastroenterology (January 2002; 122(1):44–54) compared colonoscopic biopsy samples from 305 patients with inflammatory bowel disease and 40 healthy controls. The investigators reported significantly higher concentrations of bacteria penetrating the intestinal mucosa in patients with IBD. In healthy individuals, the intestinal lining typically prevents such bacterial invasion, suggesting compromised barrier function in IBD.
The review in the Scandinavian Journal of Gastroenterology also discussed alterations in bacterial populations observed in Crohn’s disease. Patients tended to have reduced levels of Bifidobacteria, along with increased proportions of Bacteroides, Eubacteria, and Peptostreptococcus species.
Probiotics—defined as preparations containing live microorganisms—were discussed as a subject of investigation in this context. Common probiotic organisms include lactic acid–producing bacteria such as Lactobacillus, Bifidobacterium, and Streptococcus species. The authors described proposed mechanisms by which these organisms might influence intestinal health, including modulation of intestinal pH, production of antimicrobial substances, effects on nutrient absorption, and interaction with immune signaling pathways. The review emphasized that responses vary among patients and that probiotic interventions remain an area of ongoing research in inflammatory bowel disease.
