Germ tube test shows no constriction in an oral yeast culture; which organism is most likely?

• A. Candida albicans
• B. Candida krusei
• C. Cryptococcus neoformans
• D. Aspergillus fumigatus

Answer: (A)

Germ tube formation in a serum incubation test identifies Candida albicans by producing true germ tubes that extend from the yeast cell without a constricted neck. When an oral yeast culture shows a germ tube with no constriction at the base, it points to Candida albicans because this species forms such unconstricted germ tubes under these conditions. The other organisms listed do not form germ tubes in this assay (Candida krusei and Cryptococcus neoformans are germ tube negative), and Aspergillus fumigatus is a mold, not a yeast, so it wouldn’t produce germ tubes in this test.