Immunogold labeling of intracellular and extracellular M. paratuberculosis. A single macrophage is shown at 48-h postinfection (A). (B) An enlargement of the boxed region in panel A showing immunogold labeling of intracellular M. paratuberculosis. (C) Preparation of M. paratuberculosis cultured in Middlebrook 7H9 medium. Gold particle labeling was seen predominantly at the periphery of the mycobacterial cells. Magnification: 11,180 × (A); 104,000 × (B); 88,400 × (C).