Morphologic Features of Yeast Colonies

Yeast will grow on bacteriological media (sheep blood agar and chocolate agar). They may appear as small, creamy or white colonies that are somewhat more raised than staphylococcal colonies.

Yeast colonies on agar

Yeast colonies on agar

A presumptive identification of Candida albicans can be made by observing pasty, yellow-white colonies from which “feet” extend out from the margins into the surrounding agar.

Candida albicans on Blood Agar

Candida albicans on Blood Agar

Candida albicans on Chocolate agar - notice the starry colonies

Candida albicans on Chocolate agar – notice the starry colonies

Candida species are generally creamy white, although Candida krusei exhibits a flat, dry colony morphology. Here is a Macrophotograph showing a petri dish culture of the yeastlike organism (fungus) Candida krusei, after 10 days growth on Sabouraud dextrose agar. This species is known to be a food spoilage organism.

Candida krusei

Candida krusei

The distinctly mucoid appearance of the colonies in image B provides for a presumptive identification of Cryptococcus species with its production of abundant polysaccharide capsular material.

Sabouraud agar plate showing Cryptococcus neoformans colonies

Sabouraud agar plate showing Cryptococcus neoformans colonies

Rhodotorula rubra can virtually be recognized by the distinctive orange-red pigmentation of the colonies, as seen in

colony of Rhodotorula Rubra

colony of Rhodotorula Rubra

Colonies that demonstrate characteristic morphology should be examined by wet mount to confirm the presence of a yeast in culture.

Share This Post

Related Articles

Leave a Reply

You must be Logged in to post comment.

© 2018 Medical Laboratories. All rights reserved. Site Admin · Entries RSS · Comments RSS
Powered by WordPress · Powered by Medical Labs