LUMINAL BACTERIA AND SMALL-INTESTINAL PERMEABILITY

Background: The influence of luminal bacteria on small-intestinal perm eability has not been fully assessed. This study addressed this issue. Methods: Thirty-four subjects (mean age 64 years; range 22-95 years) were investigated for possible small-intestinal bacterial overgrowth ( SIBO) with culture of a small-intestinal aspirate. A lactulose/mannito l small-intestinal permeability test was performed, small-intestinal h istology assessed and serum vitamin B-12 concentrations measured in al l subjects. Permeability was also assessed in a control group of 34 as ymptomatic volunteers. Results: Urinary lactulose/mannitol ratios were significantly increased in subjects with SIBO with colonic-type flora (P < 0.0005), even in the absence of villous atrophy. Urinary lactulo se/mannitol ratios were increased in this group due to significantly i ncreased urinary lactulose concentrations (P < 0.0005) rather than red uced urinary mannitol levels, after correcting for inter-subject varia tions in renal function. Counts of intraepithelial lymphocytes of CD8 phenotype were significantly increased in this group (P = 0.003). Alth ough a significant correlation was found between intraepithelial lymph ocyte counts and small-intestinal permeability overall (P < 0.002), th ese counts were not significantly different in subjects with SIBO with colonic-type flora whose permeability values were less than or equal to or > 0.028, the upper limit of normal in asymptomatic controls. Ser um vitamin B-12 concentrations did not differ significantly between gr oups (P > 0.5). Ageing did not independently influence small-intestina l permeability (P > 0.5). Conclusions: Small-intestinal permeability i s increased in subjects with SIBO with colonic-type bacteria. This eff ect is independent of ageing and not mediated by vitamin B-12 deficien cy. Although counts of intraepithelial lymphocytes of CD8 phenotype ar e increased in this disorder, it is also unlikely that these cells pla y an important causative role in this process. Routine light microscop ic assessment underestimates the prevalence of small-intestinal functi onal disturbance in this disorder.