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Association between a large plasmid and 15- to 17-kilodalton antigens in virulent Rhodococcus equi
1Department of Animal Hygiene, School of Veterinary Medicine and Animal Sciences, Kitasato University, Aomori, Japan.
Abstract:
Rhodococcus equi strains showing 15- to 17-kDa antigens in immunoblots were found to be virulent in mice. To study the genes specific to these antigens in virulent R. equi, we compared plasmid profiles, immunoblot profiles, and murine pathogenicity profiles of 10 strains of R. equi. All the strains showing 15- to 17-kDa antigens contained a large plasmid of approximately 85 kbp and were virulent in mice; however, the remaining strains lacked both the antigens and the large plasmid and were avirulent in mice. Mutants of virulent strains ATCC 33701 and L1, which were cured of the large plasmid by repeated passage at 38 degrees C, lacked the 15- to 17-kDa antigens and showed a dramatic decrease in lethality in mice. These results suggested that the presence of an 85-kbp plasmid may be essential for virulence and expression of 15- to 17-kDa antigens of R. equi and offered support for earlier observations that freshly isolated strains of R. equi killed mice, whereas laboratory-adapted strains did not.
Insights
Virulent Rhodococcus equi strains possess a large 85-kbp plasmid essential for expressing 15- to 17-kDa antigens and causing disease in mice. Loss of this plasmid renders strains avirulent.
Area of Science:
- Microbiology
- Veterinary Science
- Molecular Biology
Background:
- Rhodococcus equi is an important pathogen in foals and immunocompromised humans.
- Virulence factors of R. equi are not fully understood, but certain antigens are associated with pathogenicity.
Purpose of the Study:
- To investigate the genetic basis of virulence in Rhodococcus equi.
- To determine the role of specific antigens and plasmids in R. equi pathogenicity.
Main Methods:
- Comparative analysis of plasmid profiles, immunoblot profiles, and murine pathogenicity of 10 R. equi strains.
- Generation and analysis of plasmid-cured mutants from virulent strains.
Main Results:
- All virulent R. equi strains possessed a large 85-kbp plasmid and expressed 15- to 17-kDa antigens.
- Avirulent strains lacked both the plasmid and the antigens.
- Plasmid-cured mutants lost the antigens and exhibited significantly reduced lethality in mice.
Conclusions:
- The 85-kbp plasmid is crucial for the expression of 15- to 17-kDa antigens in R. equi.
- This plasmid appears essential for the virulence of R. equi in a murine model.
- Findings support the association between plasmid presence, antigen expression, and pathogenicity in R. equi.