Identification of Mycobacterium avium subspecies paratuberculosis in raw and pasteurized milk samples using culture, IS900 PCR and IS900 nested PCR methods

Mycobacterium avium subspecies paratuberculosis (MAP), the causative agent of Johne’s disease, is a very slow-growing bacterium that imposes heavy costs on livestock-related industries. Due to the similar clinical and pathological symptoms in Johne’s and Crohn’s diseases, MAP is likely to play a role in the development and progression of Crohn’s disease. Hence, the possibility of transferring MAP through milk has created many concerns. To investigate the status of MAP contamination in raw and pasteurized milk samples in Kerman province, three diagnostic methods, including culture, IS900 PCR, and IS900 nested PCR was used. The results showed that the level of contamination with MAP in raw milk was relatively high in the studied herds. Based on culture, PCR, and nested PCR assays, 4.38%, 9.16%, and 13.55% were found positive, respectively. In pasteurized milk samples, 1.12%, 3.93%, and 6.18% were found positive for MAP by culture, PCR, and nested PCR, respectively. Comparing the methods used in this study demonstrated the best capability of nested PCR to detect MAP contamination. High levels of MAP contamination in raw milk on the one hand and relatively high resistance to thermal treatments, along with its intracellular characteristics, cause more survival of this bacterium, especially in the milk pasteurization process. Therefore, food hygiene researchers should pay more attention to the public health hazard caused by this bacterium.