Here disclosed is a method of preparing an antimicrobial strain composition from milk, a raw egg and a plant part, which includes the following steps: 1) providing a dairy composition comprising milk, a fermentable sugar, and edible starters from each of Lactobacillus, Bifidobacterium and Acetobacter, combining a first aliquot of the dairy composition (part A) with Rhizopus oryzae, Aspergillus niger and/or Aspergillus oryzae, and an edible starter from Saccharomyces, and conducting fermentation so as to enable the part A composition to substantially turn into a milk curd, 3) combining a second aliquot of the dairy composition (part B) with a raw egg, conducting fermentation so that eggshell substantially dissolves into the part B composition, making an opening on an eggshell membrane(s) without substantially affecting the construction of the eggshell membrane(s), and continuing fermentation of the part B composition until appearance of calcium particles on an inner surface of the eggshell membrane(s), 4) combining the part A composition obtained from step 2) and the part B composition obtained from step 3), and introducing thereinto the plant part and a fermentable sugar, so as to form an AB composition wherein casein is located on top of the AB composition, and 5) allowing the AB composition to ferment until a microbial membrane that is capable of growth develops on top of the AB composition and a liquid part forms underneath, and the liquid part is demonstrated anti-mould activity and has a pH≤；about 3.0
