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

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