Survival and Dormancy ofMycobacterium aviumsubsp.paratuberculosisin theEnvironment

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Abstract
The survival ofMycobacterium aviumsubsp.paratuberculosiswas studied by culture of fecal material sampled at intervals for up to 117 weeks from soil and grass in pasture plots and boxes. Survival for up to 55 weeks was observed in a dry fully shaded environment, with much shorter survival times in unshaded locations. Moisture and application of lime to soil did not affect survival. UV radiation was an unlikely factor, but infrared wavelengths leading to diurnal temperature flux may be the significant detrimental component that is correlated with lack of shade. The organism survived for up to 24 weeks on grass that germinated through infected fecal material applied to the soil surface in completely shaded boxes and for up to 9 weeks on grass in 70% shade. The observed patterns of recovery in three of four experiments and changes in viable counts were indicative of dormancy, a hitherto unreported property of this taxon. Adps-like genetic element andrelA, which are involved in dormancy responses in other mycobacteria, are present in theM. aviumsubsp.paratuberculosisgenome sequence, providing indirect evidence for the existence of physiological mechanisms enabling dormancy. However, survival ofM. aviumsubsp.paratuberculosisin the environment is finite, consistent with its taxonomic description as an obligate parasite of animals.