The present invention relates to novel Salmonella mutants, to a process for producing same and to vaccines containing same, wherein said Salmonella mutants are characterized in that they elicit a humoral response that can be distinguished from the humoral response elicited by the wild type strains. It is accordingly an object of the present invention to provide the use of said Salmonella mutants as serological marker strains in the vaccination of animals, in particular mammals and birds, more in particular cattle, poultry and pigs. The serological marker vaccine is of special value in animal farming and provides a (long-lasting) immunization against a wide range of Salmonella strains. The novel mutants are non-reverting and can be used for the efficient immunization of mammals and birds.
