Evaluation of Mycobacterium Avium Subsp. Paratuberculosis Transport In Saturated Porous Media

Mycobacterium avium subsp. paratuberculosis (Map) is the causative agent of Johne's disease, a chronic enteric infection that affects ruminants. Eradication of Map from infected farms has been difficult and is likely due to long-term survival of the organism in the environment. The application of Map infected animal waste can result in the leaching of this pathogen through the vadose zone and into groundwater supplies. It is also possible that soil properties inhibit transport of the organism, thereby maintaining high concentrations of Map on the soil surface and making it readily accessible for consumption by susceptible animals. Even though Map is recognized as an important pathogen, very little is known about its transport behavior through soil and aquifer materials. We performed a series of laboratory column experiments to investigate the role geochemistry has on the transport of Map through saturated porous media. The concentration of Map was determined by targeting the IS900 sequence in extracted DNA by using quantitative, real-time PCR. We found that increasing ionic strength resulted in a decrease in the electrophoretic mobility of Map (-39 mV and -24 mV at 1mM and 10 mM KCl, respectively) and decreased the transport of Map through negatively-charged quartz sand (3.1±0.07%, 2.0±0.7%, 7.7±8.4 X 10^-4% at 0.1 mM, 1 mM and 10 mM KCl, respectively), both observations in qualitative agreement with DLVO theory. We also observed that the transport of Map through positively-charged Fe-coated sands was significantly less than the transport observed through negatively-charged uncoated quartz sands, although the amount recovered from both columns was very low suggesting that Map is relatively immobile through soil and aquifer materials. Our results indicate that surface charge is a primary mechanism controlling Map transport through porous media and that the potential for significant subsurface transport of Map may be low.