This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Postrenal transplant patient presents with diarrhoea after 3 months; it was showing organism measuring 2-6 micron meter and kinoyn stain positive. Most likely it is caused by: 
Select and explain. 
A. Balantidium coli, B. Clostridium difficile, C. Cystoisospora belli, D. Cryptosporidium hominis
D: Cryptosporidium hominis
Answer: D: Cryptosporidium hominis 
Explanation: Ans. d. Cryptosporidium hominisOppounistic infections are extremely common post-transplant in the period staing from 1 month post-transplant to 6 months post-transplant.Clostridium difficle is usually seen within 1 month post-transplant because of profound antibiotic use.Kinoyn stain (Modified acid fast) positivity rules out Balantidium.Now it is between cryptosporidium vs cycloisospora. Size (smaller i.e., 2-6 microns) tells us that the organism is undoubtedly cryptosporidium hominis (previously parvum).