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Capsule-negative Staphylococcus aureus induces chronic experimental mastitis in mice
Lorena P N Tuchscherr1, Fernanda R Buzzola, Lucía P Alvarez
1Departamento de Microbiología, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155 P-12, (C 1121 ABG) Buenos Aires, Argentina.
Infection and Immunity
|November 22, 2005
Summary
Staphylococcus aureus lacking a capsule persisted longer in mouse mammary glands, unlike encapsulated strains which caused more inflammation. Capsule loss may enhance chronic infection persistence.
Area of Science:
- Microbiology
- Immunology
- Veterinary Science
Background:
- Staphylococcus aureus capsular polysaccharides (CP) are linked to virulence.
- Human S. aureus strains often express CP5 or CP8, but bovine mastitis isolates in Argentina are frequently capsule-negative.
- The role of CP in bovine mastitis pathogenesis is not fully understood.
Purpose of the Study:
- To investigate the impact of CP5 and CP8 expression on the pathogenesis of experimental murine mastitis.
- To compare the virulence and host response to encapsulated versus acapsular S. aureus strains in a mouse model.
Main Methods:
- Lactating mice were infected via intramammary route with isogenic S. aureus strains (CP5, CP8, or acapsular).
- Bacterial load was quantified at 12 days post-infection.
- Histopathological analysis assessed mammary gland inflammation.
- In vitro assays evaluated bacterial internalization by bovine epithelial cells.
Main Results:
- Acapsular S. aureus strains showed significantly higher recovery rates from infected mammary glands compared to encapsulated strains.
- Encapsulated strains induced greater leukocyte infiltration and congestion; CP5 elicited more inflammation than CP8.
- Acapsular S. aureus was internalized more readily by MAC-T cells than encapsulated strains.
Conclusions:
- S. aureus lacking a capsule demonstrated enhanced persistence in the murine mammary gland.
- Encapsulated strains induced a stronger inflammatory response and were cleared more rapidly.
- Loss of CP5 or CP8 may contribute to the persistence of S. aureus in chronically infected mammary glands.