Influence of probiotics and other external factors on intestinal biochemical microflora-associated characteristics : studies in vitro and in vivo in gnotobiotic mice and in pigs

Abstract

The benefit of harboring a balanced intestinal microflora is well recognized. Therefore, in order to 'maintain or improve the intestinal flora, the use of microbial species as feed supplements, i.e. probiotics, has rapidly increased. Additionally, antibiotics and other means for health and growth- promoting purposes are currently used.

This thesis addresses the influence of different ways of modulating the microflora, namely probiotics and/or other exogenous factors, on some biochemical Microflora-Associated Characteristics, MACs. The MACs analyzed were: conversion of cholesterol to coprostanol and of bilirubin to urobilinogen, deconjugation of taurodeoxycholic acid (TDCA) and of glycodeoxycholic acid (GDCA), production of short-chain fatty acids (SCFAs), inactivation of fecal tryptic activity (FTA), degradation of mucin and of beta-aspartylglycine, and beta-glucuronidase activity.

In the first part, seventeen probiotics belonging to the genera Bacillus, Bifidobacterium, Enterococcus, Lactobacillus and Streptococcus were screened for their capability to alter the MACs in vitro and/or in vivo in gnotobiotic mice. When tested, seven probiotics were able to deconjugate both TDCA and GDCA and four expressed beta-glucuronidase activity, in vitro. Nine of the mono-associated groups had significantly higher total SCFA concentrations in their large intestinal contents than the germ-free controls. The other parameters tested were not influenced by any of the probiotics. The results show that the probiotics tested only exert only minor influences on the MACs investigated. However, absence of a function per see, does not exclude an effect upon that function when a probiotic strain is acting within an intestinal ecosystem.

In the second part, the effect of health and/or growth promoters on six MACs was studied in piglets. The environmental influence was investigated by rearing piglets either indoors or outdoors. Alterations were observed in three MACs. Influence of probiotics and/or antibiotics was addressed by supplementing the diet to weaned piglets. Zinc bacitracin (ZB), B. licheniformis or both supplements were added to the diet until ten weeks of age. ZB and B. licheniformis influenced three MACs. Taken together the results show that the MACs investigated were rapidly established in piglets and a possible higher exposure to functionally active microorganisms occurred in the indoor than in the outdoor environment. Moreover, influences of different environmental systems, ZB and B. licheniformis on the MACs investigated occurred mainly at young ages. However, disturbances on biochemical functions might have been overcame by a 'healthy adult microflora' at completion of both experiments.

Our results add new insights related to specific functions of probiotics. It seems reasonable to assume that this approach should be used in future selection of microbial strains for health- and growth- promoting purposes. Comparative studies in germ-free and gnotobiotc animals underline the importance of a functionally active microflora in the establishment and maintenance of host-microbe and microbe-microbe 'cross-talks' in any organism. The investigation of the intestinal ecosystem in terms of functionality, i.e. the MAC concept can be applied on all levels of interactions.