Comparison of culture and PCR methods for detection of Mycobacterium avium subsp. paratuberculosis in raw milk of apparently healthy cattle

Mycobacterium avium subsp. paratuberculosis is the etiological agent for Johne’s disease which is known as chronic disease in cattle and may attribute to Crohn’s disease in human. High prevalence of Mycobacterium avium subsp. paratuberculosis has been reported in dairy cattle worldwide. Recognition of infected animals is a major factor to control the spread of the organism. In this regard, detection of the bacterium in milk of clinically suspicious and apparently healthy cows is the best way to control the infection. Although isolation of Mycobacterium avium subsp. paratuberculosis by culture assay is considered as the gold standard, PCR method helps us to recognize the occurrence of slow-growing microorganisms in a short period of time with high sensitivity. In this survey, a total number of 160 cow milk was sampled and cream layer together with the pellet of each sample was tested by PCR and culture technique. Using Kappa statistics it was revealed an almost perfect agreement between culture and PCR assay with a product size of 400 bp; however, the agreement between culture and PCR with product size of 228 bp was found substantial. Results showed a substantial agreement between PCR with product sizes of 400 bp and 228 bp. Comparing the agreement between the two PCR approaches with culture assay as gold standard test, it was assumed that PCR could be a robust and rapid method to detect Mycobacterium avium subsp. paratuberculosis in milk. Consequently, PCR can be introduced as a screening test for detection of the bacterium in cow milk.