Mechanisms That Control Bacterial Populations in Continuous-Flow Culture Models of Mouse Large Intestinal Flora

Abstract

A previous study had established that anaerobic continuous-flow (CF) cultures of conventional mouse cecal flora were able to maintain the in vivo ecological balance among the indigenous bacterial species tested. This paper describes experiments designed to determine the mechanisms which control the population sizes of these species in such CF cultures. One strain each of Escherichia coli, Fusobacterium sp., and Eubacterium sp. were studied. Growth of these strains in filtrates of CF cultures was considerably more rapid than in the CF cultures themselves, indicating that the inhibitory activity had been lost in the process of filtration. Growth rates to match those in CF cultures could be obtained, however, by restoring the original levels of H2S in the culture filtrates. The inhibitory effect of H2S in filtrates and in dialysates of CF cultures could be abolished by adding glucose or pyruvate, but not formate or lactate. The fatty acids present in CF cultures matched those in the cecum of conventional mice in both quality and concentration. These acids could not account for the slow rates of growth of the tested strains in CF cultures, but they did cause a marked increase in the initial lag phase of E. coli growth. The results obtained are compatible with the hypothesis that the populations of most indigenous intestinal bacteria are controlled by one or a few nutritional substrates which a given strain can utilize most efficiently in the presence of H2S and at the prevailing conditions of pH and anaerobiosis. This hypothesis consequently implies that the populations of enterobacteria, such as the E. coli strain tested, and those of the predominant anaerobes are controlled by analogous mechanisms.

Aspartate metabolism is involved in the maintenance of enterohaemorrhagic Escherichia coli O157:H7 in bovine intestinal content

“…Further experiments should be performed to explore differences in regulation of the asp operon between the two bacterial strains. The fact that EHEC is more efficient than commensal E. coli in assimilating aspartate is consistent with the Freter's nutrient-niche theory that postulates that a microorganism can coexist in the mammal intestine by utilizing limiting nutrients better than the other bacterial species (Freter et al, 1983) and supports a key role for aspartate during EHEC multiplication in the bovine gut.…”

“…In conclusion, it is accepted that the growth rate of a particular bacterium in the intestine is defined by its ability to occupy different ecological niches (Freter et al, 1983). If the key role of aspartate in EHEC multiplication is confirmed in the bovine intestine in vivo, an ecological strategy (e.g., the use of probiotics with a high affinity for aspartate) could be considered in future studies in order to reduce EHEC carriage before slaughter and to limit food contamination.…”

Colonization resistance and microbial ecophysiology: using gnotobiotic mouse models and single-cell technology to explore the intestinal jungle

“…Further evidence that CR could be largely directly mediated by the microbiota stems from in vitro gut fermentation models in continuous flow (CF) cultures. CF cultures can be inoculated with human or animal fecal material and, under controlled pH, temperature, and oxygen conditions, different regions of the intestinal tract can be modeled (Freter et al, 1983b;Payne et al, 2012). These systems are employed to assess the impact of probiotics, food additives, dietary components or drugs on microbiota composition or metabolism.…”

“…by antibiotics, drugs) of the microbial ecosystem are more readily achieved in CF models than in animal models or human studies. CR is provided in anaerobic CF cultures, as demonstrated by repression of E. coli growth (Freter et al, 1983b). Further disturbance of the microbiota in CF cultures alleviates CR and leads to increased titers of S. Typhimurium, Freter et al (1983a, b) states that the populations of most indigenous intestinal bacteria are controlled by substrate competition, that is, that each species is more efficient than the rest in utilizing one or a few particular substrates and that the population level of that species is controlled by the concentration of these few limiting substrates (Freter et al, 1983a, b).…”

Protective effect of intranasally inoculated Lactobacillus fermentum against Streptococcus pneumoniae challenge on the mouse respiratory tract

“…This was reinforced by experiments eval- uated at the ultra structural level, using electron microscopy [22]. The mechanisms suggested in the protective e¡ect of probiotic microorganisms [16] are very broad: from competitive exclusion [17], nutrient competition [31], production of antagonistic substances (lactic acid, hydrogen peroxide [32], bacteriocins [33]) up to immune system stimulation [14,15]. From the results obtained in the present paper, it can be suggested that the intervention of the immune system could be involved as one of the main mechanisms responsible for the protective e¡ect exerted on S. pneumoniae infection and is based on the following grounds:…”