Definition: - Stock cultures are those cultures of microorganisms that are stored or maintained for future use in such a fashion that their growth and productive capacities remains unaltered.There are two types of stock cultures: (i) working stocks and (ii) Primary stocks.· The working stock cultures are those which are used frequently and they must be maintained in a vigorous and uncontaminated condition.
These cultures are maintained as agar slants, agar stabs, spore preparations or broth cultures and they are held under refrigeration. They must be checked constantly for possible changes in growth characteristics, nutrition, productive capacity and contamination.· Primary stocks are cultures that are held in reserve for practical or new fermentations, for comparative purposes, for biological assays or for possible later screening programs.