Isolation and Identification of Yeasts from Natural Habitats

Yeasts are relatively easy to isolate from natural habitats, the technique being to weigh out a sample of the substrate, suspend it in sterile water, and streak or spread a suitable dilution on either a nonselective medium (usually acidified malt extract agar to suppress bacterial growth) to obtain specimens of the total population, or on a selective medium to obtain cultures of particular species (1 ,2 ). After the plates have been incubated at an appropriate temperature and colonies have developed, these are examined under a dissecting microscope to select at least one of each colony type. Unfortunately, many yeasts cannot be distinguished immediately by visual examination of either the vegetative cells or the colonial morphology, so that it is better to isolate as many colonies as can be handled, for identification.