Which parasite’s mature cysts are commonly observed on iodine-stained stool concentrates?

• A. Entamoeba coli
• B. Ehrlichia histolytica
• C. Giardia lamblia
• D. Cryptosporidium parvum

Answer: (A)

The test is about recognizing which cyst form is most readily seen in iodine-stained stool concentrates. Iodine highlights internal structures like nuclei, making multinucleate cysts stand out. Mature cysts of Entamoeba coli are large and commonly contain up to eight nuclei, making them easy to identify in iodine-prepared concentrates. This characteristic multinucleation is a hallmark that labs rely on to spot Entamoeba coli, which is nonpathogenic and frequently observed in routine stools. In contrast, Cryptosporidium parvum oocysts are too small and require acid-fast or fluorescent stains; Giardia lamblia cysts are typically detected with other stains or methods and aren’t as classically seen as mature cysts in iodine concentrates; Entamoeba histolytica cysts do have multiple nuclei but usually fewer (up to four) and are associated with pathogenic infection; Ehrlichia histolytica is not a stool parasite. So the best answer is Entamoeba coli.