USE OF SHAKEN CULTURES IN THE ASSIMILATION TEST FOR YEAST IDENTIFICATION

Abstract

The assimilation test, using liquid media in standing culture, is a fundamental diagnostic test in the taxonomy of yeasts (Wickerham and Burton, 1948; Wickerham, 1951). The incubation period for this method has been standardized at 20 to 24 days. This long incubation is necessitated by the occurrence of slow or adaptive metabolic reactions of certain species, especially those which are oxidative rather than fermenta-tive. Often some of these nonfermentative isolates show a variable reaction at the conclusion of the incubation period, thus making an interpretation of the assimilatory response of the organism quite difficult. In the course of extensive investigations of the marine-occurring yeast flora of Biscayne Bay Florida, studies were begun on the effect of shaking on the assimilation test. Many of our marine isolates, especially members of Rhodo-torula, exhibited latent, weak, or variable assimi-latory patterns, thus making it desirable to establish whether more definitive reactions could be developed by using agitation during the growth of the yeast. MATERIALS AND METHODS Cultures. The following species of yeasts used in this study were collected from various sediments in Biscayne Bay, Florida. These isolates included: Hansenula anomala (MY-38), De-baryomyces kloeckeri (MY-19), Cryptococcus lau-rentii (MY-76), Candida tropicalis (MY-139), and the following species of Rhodotorula: R.