Environmental Mycobacterium avium subsp. paratuberculosis Hosted by Free-Living Amoebae

Abstract

<i>Mycobacterium avium</i> subsp. <i>paratuberculosis</i> is responsible for paratuberculosis in animals. This disease, leading to an inflammation of the gastrointestinal tract, has a high impact on animal health and an important economic burden. The environmental life cycle of <i>M. avium</i> subsp. <i>paratuberculosis</i> is poorly understood and several studies suggest that free-living amoebae (FLA) might be a potential environmental host. FLA are protozoa found in water and soil that are described as reservoirs of pathogenic and non-pathogenic bacteria in the environment. Indeed, bacteria able to survive within these amoebae would survive phagocytosis from immune cells. In this study, we assessed the <i>in vitro</i> interactions between several strains of <i>M. avium</i> subsp. <i>paratuberculosis</i> and <i>Acanthamoeba castellanii</i>. The results indicate that the bacteria were able to grow within the amoeba and that they can survive for several days within their host. To explore the presence of <i>M. avium</i> subsp. <i>paratuberculosis</i> in environmental amoebae, we sampled water from farms positive for paratuberculosis. A <i>M. avium</i> subsp. <i>paratuberculosis</i> strain was detected within an environmental amoeba identified as related to the poorly described <i>Rosculus</i> genus. The bacterial strain was genotyped, showing that it was similar to previous infectious strains isolated from cattle. In conclusion, we described that various <i>M. avium</i> subsp. <i>paratuberculosis</i> strains were able to grow within amoebae and that these bacteria could be found on farm within amoebae isolated from the cattle environment. It validates that infected amoebae might be a reservoir and vector for the transmission of <i>M. avium</i> subsp. <i>paratuberculosis</i>.