Influences of some exogenous factors on the gastrointestinal ecosystem

Abstract

An intestinal ecosystem has three major actors, i.e., the macroorganism, the microflora and the environment. Influences of some exogenous factors on functions of the intestinal microbes and their interactions within the ecosystem in vivo, have been studied by utilizing the so-called microflora-associated characteristic (MAC)/germ-free animal characteristic (GAC) concept. The parameters were bile acid, urobilinogen, cholesterol faecal tryptic activity (FTA) mucin, beta-aspartylglycine, short-chain fatty acids (SCFAs).

The establishment of MACs h 35 germ-free rats was followed. The microbes were introduced in different ways and a faecal enema and social contacts with conventional rats gave rapidly an development of microbial functions. The establishment could be clustered into two groups, I) a rapid development probably depending on the microbes involved ll) a wider time range, probably depending on the way of introduction. The influence of diet was investigated in patients with Crohn's disease, receiving total parenteral nutrition (TPN) and in healthy volunteers given a balanced diet, enteral nutrition (EN), by following six MACs. The results showed greater influence of TPN than EN on bile acids, cholesterol and FTA.

Diarrhoea is one of the most common side-effects of antimicrobial treatment, so-called antibiotic-associated diarrhoea (AAD). SCFAs were investigated in 31 AAD patients and the total amount SCFAs and their distribution were significantly changed compared to healthy adults. Five other MACs were also studied and formation of coprostanol and urobilinogen and faecal tryptic activity were significantly altered in the AAD patients compared to healthy persons. Six MACs were studied in nine AAD patients given a faecal enema. Most of the patients were cured within 4 days. No relapses occurred within 18 months. Different probiotics have been used in order to avoid diarrhoea connected with antimicrobial treatment and an investigation was performed to evaluate the influence of a probiotic on 7alpha-dehydroxylation. A suspension of Lactobacillus delbruekii and Streptococcus thermophilus (LS) was given to 20 rats together with and without clindamycin. This antibiotic has a pronounced effect on most MACs h studies of healthy human and showed similar influence in rats on 7alpha-dehydroxylation. The microbes per se in LS are not claimed to 7alpha-dehydroxylate bile acids. In the present study, 7alpha-dehydroxylation was significantly reduced in the rats receiving clindamycin alone, but concomitantly use of LS reduced significantly the antimicrobial effect. Thus, the probiotics significantly influenced on a MAC not related to the microbes per se.

In conclusion, the first contacts with microbes are of importance for the establishment of intestinal ecosystems. The metabolic activities of an intestinal ecosystem can be influenced by several exogenous factors such as diet and antimicrobial drugs. Probiotics as well as enemas containing a species-specific faecal flora may restore altered functions. The intestinal ecosystem is a complex interplay, with all main actors involved in maintaining a "balanced unbalance".