Output of bacterial metabolites as a diagnostic means

Output of bacterial metabolites reflects not only the number but the metabolic activity of certain microorganisms. In case of excess of a substrate one can observe the increased output of metabolite(s) without the overgrowth of intestinal bacteria. This matter is used for detection of malabsorption of some carbohydrates (lactose, glucose) by increased excretion of hydrogen in expired air. Another group of so-called breath tests (14C-cholylglycine, 14C-xylose) is designed to detect the bacterial overgrowth in the small intestine by measuring the rise of the concentration of 14CO2 in alveolar air. All the tests basing on the decomposition of the test substance by intestinal bacteria, have some limitations. Little is known about the microorganisms decomposing the different test substances. Significant correlations between the urinary phenols (p-cresol, phenol) and certain groups of mucosal flora (staphylococci, bacteroides) of the small intestine of rats could be found. Therefore one suggests that elucidating the origin of a bacterial metabolite is still possible in some instances, although very complicated. In conclusion, the authors refer to several reasons for failure to obtain correlations between the output of the metabolite(s) and data of bacteriological investigation.