Entamoeba coli cysts are distinguished from Entamoeba histolytica cysts by the number of nuclei in the cyst.

• A. Up to eight nuclei in E. coli cyst vs up to four in E. histolytica cyst
• B. E. coli cysts have flagella
• C. E. coli cysts are larger than E. histolytica cysts
• D. E. coli cysts lack cyst walls

Answer: (A)

Nucleus count in mature cysts is the key feature used to tell Entamoeba coli from Entamoeba histolytica. Entamoeba coli cysts can contain up to eight nuclei, while Entamoeba histolytica cysts typically contain up to four nuclei. This difference in nuclear content is the most reliable microscopic clue when identifying these two intestinal amoebae in stool samples, since both form cysts that are non-motile and surrounded by cyst walls. Size and other features can vary and are not as dependable for distinguishing them, so the nuclear count provides the simplest, most specific diagnostic criterion.