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Avirulence and immunogenicity in mice of a bovine mastitis Staphylococcus aureus mutant
1Departamento de Microbiología e Inmunología, Facultad de Ciencias Exactas, Físico, Químicas y Naturales, Universidad Nacional de Río Cuarto, Córdoba, Argentina.
Abstract:
An avirulent mutant, designated RC122, was derived from Staphylococcus aureus bovine mastitis strain RC108 after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. Mutant RC122, which was isolated on the basis of reduced colony size, showed diminished virulence in mice (LD50 of RC122: 3.1 x 10(10) cfu vs LD50 of RC108: 2.3 x 10(7) cfu). Mutant RC122 grew more slowly than its parental strain and showed decreased production of several exoproteins, such as alpha- and beta-hemolysin, DNAse and coagulase. The production of its capsule was induced only under in vivo growth conditions. Clearance studies performed in the mouse kidney revealed that the kinetics of disappearance of the mutant was similar to that of its parental strain. Protection experiments carried out by intraperitoneal administration in mice showed that mutant RC122 conferred a good degree of protection from challenge with homologous and heterologous strains.
Insights
A Staphylococcus aureus mutant, RC122, exhibits significantly reduced virulence and exoprotein production. This attenuated strain still provides protection against homologous and heterologous strains in mice.
Area of Science:
- Microbiology
- Immunology
- Veterinary Science
Background:
- Staphylococcus aureus is a significant pathogen causing bovine mastitis.
- Virulence factors contribute to Staphylococcus aureus pathogenicity.
- Attenuated strains are explored for vaccine development.
Purpose of the Study:
- To characterize an avirulent mutant (RC122) derived from Staphylococcus aureus.
- To evaluate the virulence and immunogenic properties of the mutant strain.
Main Methods:
- N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis was used to create the mutant.
- Virulence was assessed in mice using LD50 determination.
- Exoprotein production and capsule induction were analyzed.
- In vivo clearance and protection experiments were conducted.
Main Results:
- Mutant RC122 displayed significantly reduced virulence (LD50: 3.1 x 10(10) cfu) compared to the parent strain (LD50: 2.3 x 10(7) cfu).
- The mutant showed slower growth, decreased exoprotein production (alpha-hemolysin, beta-hemolysin, DNAse, coagulase), and in vivo-induced capsule production.
- RC122 demonstrated similar clearance kinetics to the parent strain in mouse kidneys.
- The mutant conferred significant protection against homologous and heterologous Staphylococcus aureus strains in mice.
Conclusions:
- Mutant RC122 is an attenuated strain of Staphylococcus aureus with diminished virulence.
- Despite attenuation, RC122 retains protective immunity, suggesting potential as a live vaccine candidate.