Biological properties of the encapsulated Staphylococcus aureus M
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Abstract:
Strain M, classified as a Staphylococcus aureus, behaves like the other rare encapsulated staphylococcal strains. It was clumping-factor negative, grew in diffuse-type colonies in serum-soft agar, and produced rapidly fatal disease in mice. Strain M was highly resistant to phagocytosis by human or mouse leukocytes and required both specific antibody and heat-labile serum factor(s) for efficient ingestion by human polymorphonuclear leukocytes. Electron micrographs confirmed the presence of a large capsule. Agglutination studies, active or passive mouse protection experiments, and opsonic studies revealed that strain M represents a new, immunologically distinct strain of encapsulated staphylococcus. Strain M differs from other known encapsulated staphylococci in several other respects: its cellular and colonial morphology is atypical; its LD(50) in the mouse peritoneal model is 100 times less than that of other mouse lethal strains; it is poorly opsonized by normal human serum; and, finally, it possesses an unusually large capsule as seen in electron micrographs.
Insights
A novel Staphylococcus aureus strain, Strain M, exhibits a large capsule and resistance to phagocytosis. This encapsulated bacterium causes rapid, fatal infections in mice and represents a new, distinct immunological strain.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Staphylococcus aureus can form capsules, influencing virulence.
- Rare encapsulated strains exhibit unique characteristics.
- Understanding encapsulated S. aureus is crucial for infectious disease research.
Purpose of the Study:
- To characterize a novel encapsulated Staphylococcus aureus strain, designated Strain M.
- To investigate the immunological and pathogenic properties of Strain M.
- To determine if Strain M represents a new distinct strain of encapsulated staphylococcus.
Main Methods:
- Phenotypic characterization: clumping-factor assays, colony morphology in serum-soft agar.
- In vivo studies: mouse models for disease lethality (LD50) and protection.
- In vitro assays: phagocytosis resistance, opsonization studies with human leukocytes and serum.
- Microscopy: electron micrographs for capsule visualization.
Main Results:
- Strain M is clumping-factor negative and exhibits atypical morphology.
- It produces rapidly fatal disease in mice with a significantly lower LD50 than other lethal strains.
- Strain M shows high resistance to phagocytosis, requiring specific antibodies and heat-labile factors for opsonization by human polymorphonuclear leukocytes.
- Electron microscopy confirms an unusually large capsule.
- Agglutination, protection, and opsonic studies indicate Strain M is immunologically distinct.
Conclusions:
- Strain M represents a novel, immunologically distinct encapsulated Staphylococcus aureus.
- Its large capsule and resistance to phagocytosis contribute to its high virulence.
- Further research into Strain M could reveal new insights into staphylococcal pathogenesis and host immune evasion strategies.