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Presence of a capsule in Erysipelothrix rhusiopathiae and its relationship to virulence for mice
Y Shimoji1, Y Yokomizo, T Sekizaki
1National Institute of Animal Health, Ibaraki, Japan.
Abstract:
Three avirulent insertional mutants of Erysipelothrix rhusiopathiae were obtained by the technique of transposon mutagenesis with the self-conjugative transposon Tn916. The interactions between murine polymorphonuclear leukocytes and parent and mutant strains were studied in vitro. In the presence of normal serum, the virulent parent strain was resistant to phagocytosis, whereas the avirulent mutant strains were efficiently phagocytosed. In the presence of immune serum, the parent and the mutant strains were both efficiently phagocytosed. Electron microscopic examination of the parent strain demonstrated the presence of a structure resembling a capsule which was absent on the mutant strains, suggesting that a capsule may be involved in virulence. This was confirmed in studies in which an avirulent mutant strain reverted to virulence following acquisition of a capsule when the transposon was lost by spontaneous excision. These results strongly suggest that virulence of E. rhusiopathiae is associated, at least in part, with resistance to phagocytosis by polymorphonuclear leukocytes and that this antiphagocytic ability of the bacterium results from its possession of a capsule.
Insights
Avirulent Erysipelothrix rhusiopathiae mutants were created using transposon mutagenesis. These mutants, lacking a capsule, were phagocytosed by leukocytes, unlike the virulent parent strain, indicating the capsule
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Erysipelothrix rhusiopathiae is a Gram-positive bacterium known to cause disease in animals and humans.
- The mechanisms underlying the virulence of E. rhusiopathiae, particularly its interaction with the host immune system, are not fully understood.
- Phagocytosis by polymorphonuclear leukocytes (PMNs) is a critical component of the innate immune response against bacterial pathogens.
Purpose of the Study:
- To investigate the role of bacterial surface structures in the virulence of Erysipelothrix rhusiopathiae.
- To elucidate the interaction between E. rhusiopathiae and murine polymorphonuclear leukocytes.
- To determine the contribution of phagocytosis resistance to bacterial pathogenicity.
Main Methods:
- Generation of avirulent insertional mutants of E. rhusiopathiae using transposon mutagenesis with Tn916.
- In vitro phagocytosis assays using murine polymorphonuclear leukocytes and both parent and mutant bacterial strains.
- Electron microscopy to examine bacterial surface structures.
- Assessment of virulence following spontaneous reversion of mutants.
Main Results:
- Avirulent E. rhusiopathiae mutants generated by transposon mutagenesis were efficiently phagocytosed by PMNs in the presence of normal serum.
- The virulent parent strain exhibited resistance to phagocytosis in normal serum, suggesting an antiphagocytic mechanism.
- Electron microscopy revealed a capsule-like structure on the virulent parent strain, absent in the avirulent mutants.
- Reversion of a mutant to virulence correlated with the re-acquisition of the capsule, confirming its role.
Conclusions:
- The capsule of Erysipelothrix rhusiopathiae plays a significant role in its virulence.
- Resistance to phagocytosis by polymorphonuclear leukocytes, mediated by the capsule, is a key factor in E. rhusiopathiae pathogenicity.
- Understanding these interactions can inform strategies for controlling E. rhusiopathiae infections.