Impact of salt concentration on persistence of Mycobacterium avium subsp. paratuberculosis in Iranian UF white cheese

Mycobacterium avium subsp. paratuberculosis (Mycobacterium paratuberculosis) is considered as a potential significant public health threat due to its possible association with Crohn’s disease in humans. This is a study aimed to investigate the effect of different salt concentrations on survival of Mycobacterium paratuberculosis during ripening and storage of Iranian ultra-filtrate-white cheese (IUFWC). For this purpose, retentate was inoculated with 2 Log cfu/g of Mycobacterium paratuberculosis. Afterwards, model cheeses were prepared with 2%, 3% and 4% of salt. Quantity of Mycobacterium paratuberculosis was estimated throughout the ripening and storage of IUFWC using F57-quantitative real time PCR (F57-qPCR) and culture assay. Along with, the populations of lactic acid bacteria as well as physicochemical properties of cheese samples were determined. According to the results, at the early stage of storage period (1 to 30 days) the number of Mycobacterium paratuberculosis was almost constant; however, it was decreased significantly (p<0.01) during the late storage period (30 to 60 days). Data also suggested that Mycobacterium paratuberculosis could persist for a longer (p<0.01) period of time in the samples made with lower (2% and 3%) salt concentration. Consequently, higher salt concentration could shorten the survival of Mycobacterium paratuberculosis in IUFWC. In addition, considering the effect of time on the persistence of Mycobacterium paratuberculosis, storage of IUFWC until the end of storage period (60 days) could inactivate more of the bacterium.