Microbiology, 2021

23.6 • Protozoan Infections of the Urogenital System 971
CHECK YOUR UNDERSTANDING
• What factors can lead to candidiasis?
• How is candidiasis typically diagnosed?
Clinical Focus
Part 3
The Gram stain of Nadia’s vaginal smear showed that the concentration of lactobacilli relative to other
species in Nadia’s vaginal sample was abnormally low. However, there were no clue cells visible, which
suggests that the infection is not bacterial vaginosis. But a wet-mount slide showed an overgrowth of yeast
cells, suggesting that the problem is candidiasis, or a yeast infection (Figure 23.23). This, Nadia’s doctor
assures her, is good news. Candidiasis is common during pregnancy and easily treatable.
• Knowing that the problem is candidiasis, what treatments might the doctor suggest?
Figure 23.23 (a) Lactobacilli are visible as gram-positive rods on and around this squamous epithelial cell. (b) This wet mount
prepared with KOH shows Candida albicans pseudohyphae and squamous epithelial cells in a vaginal sample from a patient with
candidiasis. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by Mikael
Häggström)
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23.6 Protozoan Infections of the Urogenital System
Learning Objectives
By the end of this section, you will be able to:
• Identify the most common protozoan pathogen that causes infections of the reproductive system
• Summarize the important characteristics of trichomoniasis
Only one major protozoan species causes infections in the urogenital system. Trichomoniasis, or “trich,” is
the most common nonviral STI and is caused by a flagellated protozoan Trichomonas vaginalis. T. vaginalis
has an undulating membrane and, generally, an amoeboid shape when attached to cells in the vagina. In
culture, it has an oval shape.
T. vaginalis is commonly found in the normal microbiota of the vagina. As with other vaginal pathogens, it can
cause vaginitis when there is disruption to the normal microbiota. It is found only as a trophozoite and does
not form cysts. T. vaginalis can adhere to cells using adhesins such as lipoglycans; it also has other cell-surface
virulence factors, including tetraspanins that are involved in cell adhesion, motility, and tissue invasion. In