The diatheses of animals vary depending on genetic backgrounds of the animals, and the microbial structure of an enterobacterial flora inherent in a host and the behavior of the concentration of a biological molecule sometimes vary depending on the diathesis of the host. In this case, it is needed to administer a proper probiotic.Provided is a microbial preparation for controlling the proportion of the population of bacteria belonging to the division Bacteroidetes, Firmicutes or Proteobacteria or the proportion of the population of bacteria belonging to the genus Clostridium, Lactobacillus, Bifidobacterium or Bacteroidetes in the enterobacterial florae in an animal body, and for controlling the concentration of a functional molecule contained in a living body, said microbial preparation containing a microorganism P01931 (International Accession No. BP-1931), MK-01A (International Accession No. BP-02066) or MK-03A (International Accession No. BP-02067) or a component of the microorganism.
