Standard culture method
The standard method for diagnosis of Johne's disease is isolation of M. paratuberculosis on standard bacteriological media. Shown here is one type of such media, Herrold's egg yolk agar. Growth of slow-growing, small, white-yellow colonies only on media containing mycobactin (two left tubes) is indicative of M. paratuberculosis. This test is usually done on fecal samples and typically takes 12 to 16 weeks.