Short Communication Influence of Macronutrients on Segmented Filamentous Bacteria in the Small Intestine of Mice

Segmented filamentous bacteria (SFBs) in the ileum of mice were poorly present after the feeding of milk powder as sole source of nutrition, but were abundant in animals fed on a diet based on natural ingredients. Twenty-one different purified diets were formulated so that clues could be obtained to identification of the macronutrients that may be responsible for the differential SFB promoting effects of milk powder and the natural ingredient diet. None of the purified diets induced the appearance of SFBs, suggesting that the type and amount of fat, the type ofcarbohydrate and the amount and type of fibre in the diet do not influence SFB colonisation. Alternatively, the purified diets could have lacked a substance which was present in the natural ingredient diet and is essential for SFB colonisation. Thus, although we were not able to identify nutritional factors of SFBs, it is clear that the composition of the diet is at least one factor that determines whether or not SFBs appear in the ileum of mice. Colonisation levels of SFBs in mice fed experimental diets were not associated with relative caecal weight, the percentage of fusiform-shaped bacteria in the caecum or the number of Enterobacteriaceae present in faeces. The latter three parameters were however, significantly influenced by the composition of the purified diets. K F Y WORDS-Segmented filamentous bacteria; Intestinal bacteria; Macronutrients; Mouse