Molecular characterization of Salmonella enterica subsp. enterica serovar choleraesuis field isolates and differentiation from homologous live vaccine strains suisaloral and SC-54.

Four independent molecular methods were used to characterize the Salmonella enterica subsp. enterica serovar choleraesuis live vaccine strains SC-54 and Suisaloral and to differentiate them from S. choleraesuis field isolates. Plasmid analysis revealed the presence of seven plasmid profiles. A virulence plasmid of 52-kbp was identified by hybridization with an spvB-spvC gene probe in each of the S. choleraesuis field isolates and in the Suisaloral vaccine strain, but not in the SC-54 vaccine strain. Ribotyping, performed with a gene probe that recognized 23S, 16S, and 5S rRNA genes, resulted in three closely related hybridization patterns. IS200 elements were not detected in the field isolates or in the two S. choleraesuis live vaccine strains. Macrorestriction analysis with the enzymes XbaI, SpeI, NotI, and SfiI differentiated the 29 S. choleraesuis strains included in this study into 10, 13, 8, and 13 different fragment patterns, respectively. While the Suisaloral vaccine strain showed a unique XbaI macrorestriction pattern, the fragment patterns of the SC-54 strain obtained with the different enzymes were shared by 2 to 18 S. choleraesuis field strains. A combination of plasmid analysis and macrorestriction analysis proved to be most suitable for the molecular typing of S. choleraesuis and the differentiation of both live vaccine strains from field isolates of this serovar.