Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2006
Publication Date: 5/1/2006
Citation: Patel, D., Danelishvili, L., Yamazaki, T., Marta, A., Paustian, M., Bannantine, J.P., Meunier-Goddik, L., Bermudez, L.E. 2006. The ability of Mycobacterium avium subsp. paratuberculosis to enter bovine epithelial cells is influenced by preexposure to a hyperosmolar environment and intracellular passage in bovine mammary epithelial cells. Infection and Immunity. 74(5):2849-2855. Interpretive Summary: The bacterium Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) causes Johne’s Disease, an economically important intestinal infection of ruminants such as cattle and sheep. The mechanisms by which M. paratuberculosis is able to initially establish an infection in host animals are not clearly understood. The work presented here examined the ability of M. paratuberculosis to infect cultured cells under different environmental conditions. Our findings indicate that M. paratuberculosis is better at infecting epithelial cells when it has been exposed to milk and when it is has previously infected other cells. Other scientists should benefit from the results of this work. They will be able to build on these findings in order to identify which M. paratuberculosis genes are important for the establishment of infection in host animals as well as under what conditions these genes are utilized.
Technical Abstract: Mycobacterium avium subsp. paratuberculosis is the cause of Johne’s disease in cattle and other ruminants. M. avium subsp. paratuberculosis infection of the bovine host is not well understood; however, it is assumed that crossing the bovine intestinal mucosa is important in order for M. avium subsp. paratuberculosis to establish infection. To examine the ability of M. avium subsp. paratuberculosis to infect bovine epithelial cells in vitro, Madin-Darby bovine kidney (MDBK) epithelial cells were exposed to M. avium subsp. paratuberculosis. It was observed that bacteria can establish infection and replicate within MDBK cells. M. avium subsp. paratuberculosis also has been reported to infect mammary tissue and milk, and we showed that M. avium subsp. paratuberculosis infects bovine mammary epithelial cells (MAC-T cell line). Using polarized MAC-T cell monolayers, it was also determined that M. avium subsp. paratuberculosis crosses apical and basolateral surfaces with approximately the same degree of efficiency. Because M. avium subsp. paratuberculosis can be delivered to the naive host by milk, it was investigated whether incubation of M. avium subsp. paratuberculosis with milk has an effect on invasion of MDBK cells. M. avium subsp. paratuberculosis exposed to milk entered epithelial cells with greater efficiency than M. avium subsp. paratuberculosis exposed to broth medium or water (P < 0.01). Growth of M. avium subsp. paratuberculosis within MAC-T cells also resulted in augmented ability to subsequently infect bovine MDBK cells (P < 0.001). Microarray analysis of intracellular M. avium subsp. paratuberculosis RNA indicates the increased transcription of genes which might be associated with an invasive phenotype.