Abstract: The present document discloses a method for producing a bacterial vaccine composition against bacterial diseases in animals, such as tetrapods or fish, wherein said bacterial vaccine composition comprises inactivated bacteria of the bacterium causing said bacterial diseases. The method involves exposing the bacteria to different growth conditions and then preparing a bacterial vaccine composition where the bacteria are exposed to different growth conditions. With vaccines prepared by the present method, bacterial diseases that previously had not been able to be cured could be treated or the effect of the treatment was more long-lasting.