NBME Microbiology Practice Test

Giemsa is a Romanowsky-type stain used on blood smears to highlight intracellular parasites within red blood cells. It stains nucleic acids and cytoplasm in distinct hues, making malaria parasites visible inside erythrocytes as characteristic purple structures. The thick smear helps detect even low levels of parasites, while the thin smear shows parasite morphology (ring forms, trophozoites, schizonts, and gametocytes) that supports species identification. Among the options given, malaria parasites are the classic target of Giemsa staining because the organisms reside inside red blood cells and are readily visualized after this stain. Stains used for Mycobacterium tuberculosis (acid-fast) or Clostridium difficile (different staining methods and culture/toxin assays), and fungi like Candida albicans are not typically identified primarily by Giemsa in routine practice.