Detection of Mycobacterium avium subspecies paratuberculosis in pasteurized milk by IS900 PCR and culture method

Prevalence of Mycobacterium avium paratuberculosis in commercially pasteurized milk was studied. A total of 300 commercially pasteurized milk samples were purchased from various parts of Eastern-Azerbaijan province of Iran. Two 50 ml from each sample were centrifuged. DNA extraction was performed on one of the pellets and extracted DNA was evaluated for the presence of Mycobacterium avium paratuberculosis specific IS900 by PCR assay. In order to detect viable cells of the bacterium, the second related pellet was treated with 0.75% HPC and decontaminated samples cultured on two Herrold’s egg yolk medium (supplemented with mycobactin J and amphotericin B, nalidixic acid, and vancomycin). Isolated colonies by culture method were confirmed by IS900-based PCR. Although M. avium paratuberculosis DNA was detected in 32 (10.7%) samples by PCR assay, viable bacterium was not isolated by culture method in any sample.   Key words: PCR, IS900, Mycobacterium avium paratuberculosis, pasteurized milk.