Gram Negative Spiral
A sample is taken from a vulvar ulcer in a 25-year-old sexually active African American female. The organism is a weakly staining gram-negative, microaerophilic organism. When attempting to view a smear under a microscope, no organisms are seen. Which method of visualization is most appropriate in this setting? (AIPG 2010)
|B||India ink preparation|
|C||Congo red stain|
a. The organism present is Treponema pallidum, a spirochete. No organisms are seen under light microscopy because spirochetes are too small to be visualized by this technique.
b. Use of darkfield microscope allows for visualization of the corkscrew morphology. The Ziehl-Neelsen stain is used to detect acid-fast bacteria such as Mycobacteria.
c. India ink preparations are used to visualize a capsule that is present in Cryptococcus neoformans but that spirochetes do not have.
d. Giemsa stain is used to detect Borrelia, Plasmodium, Trypanosomes, and Chlamydia species.