Agarose gel electrophoresis of amplified IS900 fragments. Lanes 1 and 6: molecular weight marker (2176, 1766, 1230, 1033, 653, 517, 453, 394, 298, 234–220, 154 bp); lanes 2 and 3: two patient samples; lane 4: positive control (Mycobacterium avium subsp. paratuberculosis type strain); and lane 5: negative control (Mycobacterium avium strain).