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Published on: February 10, 2011
Pathogenicity in mice of Staphylococcus aureus mutants deficient in exoprotein synthesis
L Odierno1, G Risatti, A Calzolari
1Departmento de Microbiología, Facultad de Ciencias Exactas, Físico, Químicas y Naturales, Universidad Nacional de Río Cuarto, Argentina.
Abstract:
Twelve mutants were isolated from a Staphylococcus aureus strain derived from bovine mastitis after mutagenesis by ultraviolet light. These mutants were found to be deficient for several characteristics such as production of most exoproteins and had altered phage type and/or colonial morphology in serum-soft agar medium. They also differed in virulence when assayed in mice by intraperitoneal administration; the ratio of the LD50 of the mutants vs. that of the parental strain ranged from 1 to 123. The different virulence of the mutants could not be associated with lack of production of exoproteins or altered colonial morphology. On the other hand, a clear correlation was evidenced between lowered virulence and slower growth rate at 37 degrees C. Three mutants were assayed in the mouse mastitis model. One of them, which was about 40 times less virulent when assayed by intraperitoneal administration, induced a histopathological lesion similar to that produced by the parent strain; the other two mutants, which were about 70 to 120 times less virulent by intraperitoneal administration, induced only a very slight lesion. Mice were vaccinated by the intraperitoneal route with two of the less virulent mutants; the LD50 in the vaccinated mice that were challenged with the parental strain increased 11 to 14 times compared with that for the unvaccinated mice.
Insights
Researchers identified Staphylococcus aureus mutants with reduced virulence. Lowered virulence correlated with slower growth, and vaccination with these mutants offered partial protection against the parental strain in mice.
Area of Science:
- Microbiology
- Bacteriology
- Immunology
Background:
- Staphylococcus aureus is a significant pathogen, particularly in bovine mastitis.
- Understanding the genetic basis of Staphylococcus aureus virulence is crucial for developing effective control strategies.
Purpose of the Study:
- To isolate and characterize Staphylococcus aureus mutants with altered virulence.
- To investigate the relationship between specific mutant characteristics and virulence.
- To evaluate the potential of less virulent mutants as vaccine candidates.
Main Methods:
- Mutagenesis of Staphylococcus aureus using ultraviolet light.
- Isolation and characterization of twelve mutants.
- Virulence assays in mice (intraperitoneal administration and mastitis model).
- Growth rate determination at 37°C.
- Vaccination studies in mice.
Main Results:
- Twelve mutants exhibited reduced exoprotein production, altered phage type, and/or colonial morphology.
- Mutant virulence (LD50 ratio) varied significantly (1 to 123) compared to the parental strain.
- Lowered virulence correlated with slower growth rates at 37°C, but not with exoprotein production or morphology.
- In the mastitis model, less virulent mutants induced less severe lesions.
- Vaccination with two less virulent mutants increased protection against the parental strain by 11-14 fold.
Conclusions:
- Slower growth rate is a key factor associated with reduced virulence in these Staphylococcus aureus mutants.
- Less virulent mutants show promise as vaccine candidates for protecting against Staphylococcus aureus infections.
- Further research is warranted to explore the mechanisms underlying growth rate-virulence correlation and to optimize vaccine strategies.
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