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ARS Home » Midwest Area » Bowling Green, Kentucky » Food Animal Environmental Systems Research » Research » Publications at this Location » Publication #251508

Title: Survivability of Mycobacterium avium subsp paratuberculosis in grass silage after fermentation and exposure to low pH and high organic acids

item FLIS, S - Miner Institute
item Cook, Kimberly - Kim
item BALLARD, C - Miner Institute

Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/4/2010
Publication Date: 5/26/2010
Citation: Flis, S.A., Cook, K.L., Ballard, C.S. 2010. Survivability of Mycobacterium avium subsp paratuberculosis in grass silage after fermentation and exposure to low pH and high organic acids. American Dairy Science Association Proceedings. Abstract only.

Interpretive Summary:

Technical Abstract: Mycobacterium avium subsp paratuberculosis (Map) is a pathogen of concern in dairy production due to its ability to withstand harsh conditions and cause new infections. Infection is a result of ingesting Map cells from contaminated feed, water, or manure. The goal of this research was to evaluate the ability of Map to survive low pH and high organic acid concentrations encountered as part of ensiling. Three experiments were conducted to evaluate survivability and the ability to differentiate live and dead cells. Study 1 evaluated survivability in grass silage fermented in vacuum bags. Forage was inoculated with live Map cells, dead Map cells, or no Map cells (control) and incubated for 25, 50, 75, or 100d. Fermented forage averaged 4.7 ± 0.11 pH, 8.3 ± 2.1 lactic acid (% DM), 3.5 ± 0.9 acetic acid (% DM), and 0.05 ± 0.03 propionic acid (% DM). Study 2 evaluated survivability in buffered citric acid solutions of pH 4, 5, 6, and 7. Live Map cells were added to solutions and cell concentrations were measured at 0, 5, 15, 20, 30, and 35 days. Study 3 evaluated survivability in exudates from control silage in study 1. Exudates were filter sterilized to eliminate background population interference and pure live Map was exposed to exudates for 0, 5, 10, 15, 20, 25, or 30 days. Study 1 found no changes in the concentration of Map cells regardless of number of days of fermentation or type of cells inoculated. After exposure to citric acid in study 2 samples were analyzed for Map concentration by PCR (total cells) and propidium monoazide (PMA; live cells). Study 2 found that live cell concentration decreased more rapidly as pH decreased and exposure time increased with a 2-fold log reduction for pH 4 at 37d. In study 3, no change in Map concentration was found when cells were exposed to exudates. These results indicate that while Map is sensitive to low pH, this only occurs with concentrations of acid higher than that seen in proper forage fermentation. Overall indicating that Map present in manure and applied to forage grasses may survive the ensilaging process and silage may therefore be a potential route of infection.