Abstract
Bovine tuberculosis is in the UK a persistent disease, affecting cattle and badgers. The latter is suspected to be a reservoir for Mycobacterium bovis but the transmission between badgers and cattle remains unclear. Mycobacteria have been shown to survive ingestion by protozoa and some even multiplied inside amoebas. The aim of this study was to investigate some interactions of Acanthamoeba castellanii and Tetrahymena pyriformis with M bovis. Firstly, the long term survival of the bacilli in protozoa was monitored. Secondly, it was investigated whether bacilli internalized in protozoa cysts are protected from hypochlorous acid and desiccation. Thirdly, the identification of M bovis in environmental protozoa isolated from badger latrines was attempted. The long term incubation of M. bovis with A. castellanii showed that the amoebas had a negative effect on the survival of virulent M. bovis. M. bovis was not detectable after 6 months of coincubation but remained viable at high concentrations in the control experiments. This effect however, could not be seen in T. pyriformis. Cysts of A. castellanii did not protect M bovis from hypochlorous acid and desiccation. Results indicate that M. bovis was more susceptible to hypochlorous acid after the encystment in comparison with the controls. These findings suggest that A. castellanii contributes to the decrease of M. bovis and therefore, it can be suggested that protozoa might have a negative impact on the survival M. bovis in the environment. In one of the samples taken from Woodchester Park, acid fast rods could be identified. Acid fast microorganisms were also identified in trophozoites of protozoa. This indicates that trophozoites of enviromnental protozoa might be carrier of mycobacteria and possibly M. bovis. An infection with bacilli-containing trophozoites might therefore be a potential route of transmission between the enviromnent and animals.