2005 Volume 16 Issue 4 Pages 111-116
To demonstrate the participation of the 95-kb virulence plasmid in the pathogenicity of S. Abortusequi in horses, the prevalence of the plasmid in S. Abortusequi field isolates was examined, and experimental inoculation of mice and horses was carried out using strains with and without the plasmid. Single, large plasmids were detected in 226 of the 242 field isolates (93.4%), and spvC was detected by PCR testing from all the isolates with the plasmid. Mouse virulence tests revealed that the LD50 of 11 of 13 isolates harboring the virulence plasmid was less than 104 CFU, whereas the LD50 of 12 isolates not harboring the virulence plasmid was, without exception, over 106 CFU. Experimentally, 6 horses inoculated with S. Abortusequi strains 17N1 or Sal-107 harboring the 95-kb virulence plasmid were infected, and showed similar clinical symptoms, even though Sal-107 is avirulent in IVCS mice. On the other hand, the 17N3 plasmid-cured strain did not infect horses. We conclude that the 95-kb virulence plasmid of S. Abortusequi plays a role as a pathogenic factor in mice, but is also important in horses.
