The invention discloses a method for producing a single bacterial strain culture of Histomonas meleagridis (H. meleagridis), the method being characterised by the following steps: (a) providing a xenic culture of H. meleagridis comprising H. meleagridis cells with a wild type bacterial flora, (b) treating the xenic culture with a mixture of antibiotics thereby killing the wild type bacterial flora, (c) centrifuging and washing the H. meleagridis cells, (d) controlling effectiveness of step (b), (e) resuspending the washed H. meleagridis cells, (f) adding one or more single bacterial strain (s) to the resuspended H. meleagridis cells, and (g) culturing the one or more single bacterial strain (s) with the resuspended H. meleagridis cells so as to obtain a single bacterial strain culture of H. meleagridis. The invention further discloses a vaccine formulation consisting of a Histomonas component consisting of an attenuated culture of Histomonas meleagridis, a bacterial component consisting of one or more cultures of a single bacterial strain, and pharmaceutically acceptable non-biological formulation compounds.
