Fecal bacterial activity in symptomatic carbohydrate malabsorption: effect on the fecal short-chain fatty acid ratio.

BACKGROUND: It is still not clear why only some patients with carbohydrate malabsorption experience symptoms. In a previous study on healthy fructose malabsorbers an increased degradation of fructose in anaerobic fecal cultures from symptomatic malabsorbers was found, indicating increased bacterial activity. In the present study, the same investigation was repeated in patients with nonspecific abdominal complaints and fructose malabsorption. Moreover fecal short-chain fatty acids (SCFA), products of colonic bacterial fermentation of carbohydrates were measured. PATIENTS AND METHODS: A standard quantity of fructose (500 mg) was added to anaerobic fecal cultures from 25 patients (nine men, 16 women; median of age 53 years, range 36-69 years). The fructose degradation rate was assessed using photometry, and interpreted as representing bacterial activity in the colon. In 14 of the patients, SCFA levels were also measured using chromatography on a capillary column. RESULTS: 10 of the 25 patients had a history of symptoms after ingesting fructose-containing foods, and also showed symptoms during the test; 6 patients had symptoms either in their history or during the test; and the remaining 9 were free of symptoms. There were no differences in the H2 increase. The fructose degradation rate was higher in symptomatic malabsorbers (255 mg vs. 217 mg), but the difference was not significant. However, there was a strong inverse correlation between this bacterial activity and the acetate level, with r = -0.822 (P = 0.000) and r = -0.868 (P = 0.000) in the rank correlation. The correlation for propionate was r = 0.479 (P = 0.083), and that for butyrate was r = 0.599 (P = 0.024). CONCLUSIONS: This study failed to confirm a significant correlation between fecal bacterial activity and the occurrence of symptoms in patients with fructose malabsorption. However, the interesting correlation with the SCFA raises questions regarding possible connections between colonic bacteria, carbohydrate malabsorption, and the beneficial effect of this pattern of SCFA in several colonic diseases.

Comparative study of Streptococcus mutans laboratory strains and fresh isolates from carious and caries-free tooth surfaces and from subjects with hereditary fructose intolerance.

This study was undertaken to investigate and compare some biochemical and physiological properties related to sugar metabolism of 4 laboratory strains and 13 freshly isolated strains of Streptococcus mutans from carious and caries-free tooth surfaces and from subjects with hereditary fructose intolerance. Growth in Trypticase (BBL Microbiology Systems)-yeast extract in the presence of various sugars was almost the same for all of the fresh isolates, which grew generally better than the laboratory strains. This was especially noticeable on sucrose where the fresh isolates (including those isolated from hereditary-fructose-intolerant patients) grew two to four times more rapidly than the laboratory strains. The rate of acid production by the fresh isolates, measured with resting cells in the presence of glucose, was quite comparable to the rate of the laboratory strains. The glucose analog, 2-deoxyglucose, inhibited the acid production from glucose by two laboratory strains (6715 and ATCC 27352), but none of the fresh isolates was affected by its presence. The antibiotic, gramicidin D, which allows free diffusion of H(+) across the cell membrane, inhibited the acid production of all of the strains. Phosphoenolpyruvate phosphotransferase activity toward alpha-methylglucoside was found in all of the laboratory and freshly isolated strains. 2-Deoxyglucose phosphotransferase activity was detected in all of the laboratory strains, but many clinical strains, especially those from hereditary-fructose-intolerant patients, contained very low or almost undetectable 2-deoxyglucose phosphotransferase activity. In one strain, the activity was restored after repeated culturing in Trypticase-yeast extract medium supplemented with glucose. Glucokinase and lactate dehydrogenase activities were detected in all of the strains tested. No marked differences were observed for these two enzymes between the fresh isolates and the laboratory strains except for three clinical strains which possessed low levels of glucokinase. The growth of all of the strains in a broth containing 4 mM glucose and 4 mM lactose was studied. Various patterns were observed: diauxie, glucose utilized before lactose but without diauxie, both sugars consumed concurrently, and lactose consumed more rapidly than glucose.