Use of ribotyping, IS200 typing and plasmid analysis for the identification of Salmonella enterica subsp. enterica serovar Typhimurium vaccine strain Zoosaloral H and its differentiation from wild type strains of the same serovar.

Fifty Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) isolates obtained from one vaccinated and three non-vaccinated poultry flocks as well as the commercially available vaccine strain Zoosaloral H and a S. Typhimurium reference strain were characterized genotypically to differentiate between S. Typhimurium live vaccine strain Zoosaloral H and wild type strains of the same serovar. Ribotyping revealed five different patterns one of which exclusively occurred in the vaccine strain. Seven different hybridization patterns could be observed by IS200-typing of the S. Typhimurium isolates; one of them was only detectable in the vaccine strain. Plasmid analysis showed that 51% of the S. Typhimurium isolates including the vaccine strain harboured large plasmids of approximately 60 MDa. Hybridization with a virulence gene probe identified only 48% of these large plasmids, including that of the vaccine strain, to carry this virulence-associated gene. However, restriction endonuclease analysis of the hybridizing plasmids showed that the virulence gene was located on HindIII fragments of different sizes in the plasmid of the S. Typhimurium vaccine strain Zoosaloral H and in the plasmids of the respective wild type S. Typhimurium isolates. Thus, ribotyping, IS200-typing and plasmid analysis represent at least three independent systems which allow the genotypic identification of the S. Typhimurium vaccine strain Zoosaloral H and its differentiation from wild type isolates of the same serovar.