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Encapsulation and mouse-virulence of Serratia marcescens strain SM-1 and its variants in relation to colonial
Abstract:
With the addition to a soft-agar medium of rabbit anti-flagella serum inhibiting mobility, strain SM-1 of Serratia marcescens produced single colonies. Strain SM-1 and its variants A and B exhibited three kinds of colonial form. The parent strain showing extra large round-type growth in the medium had the highest cell volume index and mouse virulence, and a large capsule was seen on electron microscopy. An intermediate cell volume index and a remarkably lower mouse virulence were observed with variant A, which exhibited diffuse-type growth in the medium, although no definite extracellular feature was shown. The variant B, showing compact-type growth in the medium, represented the lowest cell volume index, mouse avirulence and was not encapsulated. Mouse virulence of the parent strain was assumed to be related to encapsulation which protects against phagocytosis.
Insights
Serratia marcescens strain SM-1 and its variants showed distinct colonial forms. Mouse virulence correlated with cell size and encapsulation, suggesting capsules protect against phagocytosis.
Area of Science:
- Microbiology
- Bacteriology
- Pathogenesis
Background:
- Serratia marcescens is an opportunistic pathogen.
- Colonial morphology can influence bacterial virulence.
- Understanding bacterial surface structures is key to pathogenesis.
Purpose of the Study:
- To investigate the relationship between colonial morphology, cell characteristics, and mouse virulence in Serratia marcescens.
- To characterize variants of Serratia marcescens strain SM-1.
Main Methods:
- Cultivation of Serratia marcescens strain SM-1 and its variants in soft-agar medium with anti-flagella serum.
- Observation of colonial morphology (round, diffuse, compact).
- Measurement of cell volume index and assessment of mouse virulence.
- Electron microscopy to visualize bacterial capsules.
Main Results:
- Strain SM-1 exhibited large, round colonies, high cell volume, significant mouse virulence, and a large capsule.
- Variant A showed diffuse growth, intermediate cell volume, and lower mouse virulence.
- Variant B displayed compact growth, the lowest cell volume, avirulence, and lacked a capsule.
- Encapsulation in the parent strain was associated with increased virulence.
Conclusions:
- Colonial morphology in Serratia marcescens is linked to cell volume, encapsulation, and mouse virulence.
- Encapsulation appears to be a key factor in the virulence of Serratia marcescens, potentially by evading phagocytosis.