The dual microbial preparation for use in the preparation of the useful medicament for the treatment of human or animal symptoms of opportunistic microbial infections, in particular symptoms caused by dysbiosis, preferably in the oral cavity, in the skin, and in the vagina, wherein said preparation comprises two basic microbial components in mutual synergic action, i.e., the microscopic oomycete Pythium oligandrum and a microbiome component, whereby the microbiome component is a component of a physiological microbiome of human or animal origin.