This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
A 36 years male presented with complaints of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram-positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is 
Select and explain. 
A. Actinomyces israelii, B. Nocardia asterroides, C. Blastomyces dermaidis, D. Cryptosporidium parvum
B: Nocardia asterroides
Answer: B: Nocardia asterroides 
Explanation: Actinomyces species are not acid-fast. Nocardia species are acid-fast, they are N.asteroides and N.bresiliensis, metastatic infections may involve the brain, kidney, and other organs. Blastomyces is a dimorphic fungus. Cryptosporidium parvum is a parasite (Sporozoa) Ref: Textbook of microbiology; Ananthanarayan and paniker's; 10th edition; Pg:400