Comparison of polymerase chain reaction tests and faecal culture for detecting Mycobacterium paratuberculosis in bovine faeces

A polymerase chain reaction (PCR) test for M. paratuberculosis was developed based on a 218 bp segment of a DNA insertion sequence, IS900, that is specific for this organism. The method involved two consecutive amplification reactions, with the second set of primers being nested inside the first set. The method reliably detected 50 organisms/g faeces. This PCR test was applied to 32 bovine faecal specimens containing high, moderate or low numbers of M. paratuberculosis organisms as determined by culture. The PCR test detected all specimens containing ≥1600 colony forming units (cfu)/g faeces, six of ten specimens with 160–480 cfu/g faeces but only two of 13 specimens containing ≤ 112 cfu/g faeces. The sensitivity of this test was better than that of a commercial PCR test which was carried out on the same faecal specimens.