Microbestiary Photo Contest Third Place
About this microbe:
Though two red, oblong structures can be seen in this picture, this stain was actually negative. The purpose of this stain was to determine if the cat in our case study had cryptosporosis, a diarrheal disease caused by the parasite Cryptosporidium (Crypto). The two microorganisms found in this stain were found to be too irregular to be Crypto oocytes, but they do provide nice coloring in a negative stain.
The stain is a modified Ziehl-Neelsen stain (modified acid-fast), which is often used for fecal smears (what we did here). The oocysts of Crypto are acid fast, and thus stain red. However, other parasitic organisms will also stain red, including members of Isospora. We found in a previously run fecal float that our case study animal was infected with Isospora, and thus that’s what I suspect is stained in this image.
Crypto oocysts have a slightly different morphology than what is stained red in this photo– they are quite round, and lack the elongation and pointed ends of what is stained in this image. A positive stain would show these very small (4-6 um) very circular oocysts stained red with the white and blue background.
Image: Erin Bentley