Dairy products, such as cheese and yoghurt, are potential vehicles of transmission of Mycobacterium avium subsp. paratuberculosis(Map) to the food chain. In this study a method has been developed for the extraction and detection of Map DNA from raw and pasteurised dairy products; Gouda (semi-hard), Danish Blue (semi-soft) and Munster (soft) cheese, along with plain full fat yoghurt, artificially-contaminated with three Map strains:- NCTC 8578, Niebuell and NIZO B2962.

Cheese and yogurt samples were spiked with a range of Map inocula. Map-DNA was recovered from homogenised (sodium citrate-based) cheese and yogurt samples using the Adiapure® kit (Adiagene, France). Template DNA was assayed by real time PCR, targeting both IS900 and F57 genetic elements (ABI 7500) in addition to end point PCR using P90/P91 primers and the Adiavet® kit (Adiagene, France). Initial inoculum levels were determined by plate culturing on Herrold's Egg Yolk and Middlebrook 7H10 media.

In real time PCR assays, higher sensitivities were achieved by probes targeting IS900 than the f57 target. Using the former, Map was detectable at < 20 cfu g^-1 in the cheeses Danish Blue and Munster and yogurt whereas Map extraction and subsequent real time detection was less sensitive for the harder Gouda cheese. This may imply a more efficient Map-DNA extraction from the matrices having a higher water content. For all matrices and Map strains assessed the endpoint Adiavet® kit provided a higher rate of detection/improved sensitivity than endpoint derived P90/P91 (both based on IS900) PCR. However, the real time PCR assay represented a more sensitive molecular detection method than either end point PCR assay.

The real time PCR method coupled with the Adiapure Map-DNA extraction kit represents a reproducible, sensitive and convenient assay for the detection of Map-DNA from a range of raw and pasteurised dairy products.