Biochemical effects on germ-free mice of association with several strains of anaerobic bacteria.

The effects of the following changes throughout the association of germ-free mice with increasing numbers of anaerobic bacteria were studied: (i) elution patterns obtained by gel-filtration chromatography of caecal diffusates; (ii) concentration of beta-aspartylglycine in caecal and faecal contents; (iii) polypeptide patterns obtained by sodium dodecyl sulphate-polyacrylamide gel electrophoresis of caecal supernatants; (iv) free amino acid content of caecal supernatants; (v) faecal bile acids, analysed by gas-liquid chromatography; (vi) colonization-resistance. The results indicate that monitoring the normalization (association) process can be accomplished in several ways, but the level of colonization-resistance is most easily measured by high-voltage paper electrophoresis of faecal supernatants to determine the concentration of beta-aspartylglycine. During association, the concentration of beta-aspartylglycine decreased and became undetectable after association with 40 to 50 different strains of bacteria. There was a good negative correlation between the level of colonization-resistance and the concentration of beta-aspartylglycine.