Typical indigenous bacteria in the cecum of ddY mice fed a casein-beef tallow diet or whole-egg diet.

With the aim to prove the existence of food ingredient-susceptible indigenous bacteria (SIBs) in the gut, the gut microbiota of ddY mice fed a diet containing 20% milk casein and 17% beef tallow (CT diet) or 40% whole-egg powder (Egg diet) for 14 days were analyzed by 16S ribosomal RNA gene (V4) amplicon sequencing. At the genus level, abundance levels of Desulfovibrionaceae sp., Oscillospira, and Bacteroides were high in mice fed the CT diet. At the operational taxonomic unit level, Bacteroides acidifaciens- and Bacteroides caecimuris-like bacteria were highly abundant in mice fed the CT diet. Faecalibaculum rodentium- and Allobaculum stercoricanis-like bacteria were highly abundant in the mice fed the Egg diet. These sets of taxa were assumed to be estimates of casein-tallow SIBs and egg SIBs, respectively, in the gut microbiome. Among the SIBs, B. caecimuris and F. rodentium could be isolated using blood and liver agar. PRACTICAL APPLICATIONS: B. caecimuris and F. rodentium are regarded as casein-tallow and/or egg SIBs in mice. It is possible to demonstrate functionality with orally administered food ingredients. Isolation and application of human or livestock SIB is considered promising for the development of new probiotics and functional foods.