Germ tubes
In many laboratories, the germ tube is the starting point in the identification of a yeast. The form seen below is a yeast cell giving rise to a germ tube. The germ tube is about half the width and three to four times the length of the cell. It is a straight-sided extension from the yeast cell. If a constriction is present, this indicates the formation of pseudohyphae, rather than a germ tube.
In the classic germ tube test (where fetal bovine serum is lightly inoculated with the yeast isolate and incubated at 35 - 37° C for 2.5 - 3 hours), the production of germ tubes is usually diagnostic of Candida albicans. However, Candida dubliniensis also produces germ tubes, although the incidence of this organism is much less than C. albicans. Still, laboratories may consider reporting germ tube-positive yeasts as "Candida albicans/dubliniensis." It is recommended that a minimum of five well-defined germ tubes are observed before the isolate is called positive.
