Some safety aspects of Salmonella vaccines for poultry: in vivo study of the genetic stability of three Salmonella typhimurium live vaccines.

Live vaccine strains of Salmonella should be avirulent, immunogenic and genetically stable. Some isolates of three commercially available live vaccine strains of Salmonella typhimurium, sampled during a study on their persistence in a vaccinated flock of chickens, were analyzed for genetic stability using macrorestriction analysis of their genome. Two out of the three vaccine strains showed genetic instabilities. Two of the 51 isolates of Zoosaloral vaccine strain and nine of the 32 analyzed isolates of chi(3985), a genetically modified organism, were variants and showed different macrorestriction profiles.