A stool sample contains round cysts measuring 10 to 15 micrometers. Iodine mount shows immature cysts with one or two nuclei and glycogen vacuoles, while mature cysts contain up to four nuclei with centrally placed karyosomes and chromatoid bars with blunt, rounded ends. This morphology identifies:
- A Entamoeba dispar
- B Entamoeba coli
- C Entamoeba histolytica ✓
- D Endolimax nana
Correct answer: C. Entamoeba histolytica
Explanation
Mature E. histolytica cysts have up to four nuclei and chromatoid bodies with characteristic blunt, rounded ends. E. coli has eight nuclei and splintered, pointed chromatoid bars, while Endolimax nana has four nuclei but no chromatoid bodies. E. dispar is morphologically identical to E. histolytica on light microscopy and can be separated only by molecular methods or zymodeme analysis, which is why cyst morphology alone cannot exclude it.
Reference: Paniker's Textbook of Medical Parasitology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.