Bacteriology (microscopy)
Ziehl–Neelsen-stained smears of faeces or intestinal mucosa are examined microscopically. A presumptive
diagnosis of paratuberculosis can be made if clumps (three or more organisms) of small (0.5–1.5 μm),
strongly acid-fast bacilli are found. The presence of single acid-fast bacilli in the absence of clumps indicates
an inconclusive result. The disadvantages of this test are that it does not differentiate among other
mycobacterial species and only a small proportion of cases can be confirmed on microscopic examination of
a single faecal sample.