ARS | Publication request: Mycobacterium avium subsp paratuberculosis cells are surprisingly resistant to ensiling process.

Submitted to: Paratuberculosis Newsletter
Publication Type: Research Technical Update
Publication Acceptance Date: February 25, 2013
Publication Date: March 4, 2013
Citation: Cook, K.L., Flis, S.A., Ballard, C.S. 2013. Mycobacterium avium subsp paratuberculosis cells are surprisingly resistant to ensiling process.. Paratuberculosis Newsletter. March 2013 p7-8.

Technical Abstract: Silage is a valuable source of nutrients for dairy and beef cattle in non-forage months. The most commonly ensiled crops include corn and grass forage, both of which are often fertilized with livestock manure spread by broadcasting onto the soil or by spray irrigation. Pathogen contamination may result from application of contaminated manure or wash waters to silage crops. Die-off of undesirable microbial populations in materials undergoing the ensiling process occurs as a result of production of weak organic acids (including lactic, acetic and propionic) and concomitant decreases in pH. Pathogens of concern in silage, therefore, are those like Mycobacterium avium subsp paratuberculosis (M. paratuberculosis) which are resistant to acids and are able to withstand harsh conditions encountered in the natural environment and within the host during pathogenesis. Researchers found that while M. paratuberculosis was sensitive to direct intracellular acidification when exposed to organic acids, the organism was over 7 times less sensitive when exposed to silage exudates at the same pH. In fact, M. paratuberculosis cells showed no significant decrease in repeated silage experiments. Results from this series of studies suggest that cells of M. paratuberculosis may persist when exposed to the low pH and high organic acids that are key to the ensilaging process. Silage may be a potential route of exposure if viable M. paratuberculosis cells survive and are ingested by a susceptible animal. Given the organisms importance as a dairy pathogen, further research is needed to better understand persistence of this organism in livestock feeds.