Efficiency of direct microbial diagnosis, IS900 PCR and microbial culture for detection of Mycobacterium avium subsp. Paratuberculosis in the feces of apparently healthy cattle

Johne’s disease or paratuberculosis is a chronic granulomatous enteritis in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The disease is responsible for significant economic losses in dairy industry worldwide. Microbial culture as a golden standard test for detection of MAP in faecal specimens requires 6-16 weeks to complete, whereas accurate and rapid identification of cattle shedding MAP in their feces is essential for successful control of the disease in herds. In the present study, direct microbial diagnosis by Ziehl-Neelsen acid-fast staining, microbial culture on Herrolds’ egg yolk media and two IS900 direct PCR assays were carried out on 100 fecal specimens of apparently healthy cattle collected from dairy herds of Tabriz with a history of Johne’s disease. The number of positive specimens identified by the direct microbial diagnosis, microbial culture and PCR with F90/F91 and FP25/FP26 primes were 7 (7%), 14 (14%), 15(15%) and 25(25%) respectively. These results indicated that PCR detected more positive cases therefore it can be employed for rapid and accurate diagnosis of cattle shedding MAP it their feces and the type of primer used has a significant role in the sensitivity of this test. Direct microbial diagnosis by Ziehl-Neelsen acid-fast staining identified 7 (7%) specimens, two IS900 direct PCR assays identified 15 (15%) and 25 (25%) specimens, respectively, and microbial culture identified 7 (7%) specimens as positive. Collectively, these data indicate that PCR detection of MAP was more sensitive than direct microbial diagnosis by Ziehl-Neelsen acid-fast staining or faecal culture, especially if appropriate primers were used.