Yeasts are recovered from a wide range of aquatic, marine, atmospheric and terrestrial habitats. Many yeasts occur widely, whereas some appear to be confined to specific habitats. Yeasts seldom occur in the absence of either molds or bacteria. Consequently, selective techniques are often used for recovery of yeasts, employing media that permit the yeasts to grow, while suppressing molds or bacteria. These media exploit the fact that yeasts are generally capable of developing at pH levels and water activities that reduce or inhibit the growth of bacteria. The media may also include antibiotics or fungistatic agents for the suppression of molds (Yarrow, 1998).