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Attenuated expression of the mga virulence regulon in an M serotype 50 mouse-virulent group A streptococcal strain
D L Yung1, K S McIver, J R Scott
1Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Abstract:
The attenuated expression of virulence genes found in a group A streptococcal strain that is naturally pathogenic for mice was postulated to result from a defect in the strain's multigene regulator, Mga. The sequence of the mga gene reveals three amino acid changes in the gene product that might affect protein function. The defect in the mga gene was complemented by providing either the closely similar mga4 allele or a more divergent mga1 allele in trans. Complementation increased the amount of emm50 transcript and the quantity of surface-extractable M protein, restoring virulence function.
Insights
A defect in the Mga regulator of group A Streptococcus impairs virulence gene expression in mice. Restoring Mga function via gene complementation re-established virulence.
Area of Science:
- Microbiology
- Bacterial genetics
- Streptococcal infections
Background:
- Group A Streptococcus (GAS) causes various infections.
- Virulence gene expression is crucial for GAS pathogenesis.
- The Mga regulator controls multiple GAS virulence factors.
Purpose of the Study:
- To investigate the role of a defective Mga regulator in GAS virulence.
- To identify specific mutations within the mga gene.
- To restore GAS virulence by complementing the mga defect.
Main Methods:
- Sequencing the mga gene to identify mutations.
- Allelic exchange to introduce mga alleles.
- Quantitative reverse transcription-PCR to measure emm50 transcript levels.
- Western blotting or ELISA to quantify M protein.
Main Results:
- A GAS strain with attenuated virulence showed three amino acid changes in Mga.
- Complementation with wild-type or divergent mga alleles restored Mga function.
- emm50 transcript levels and surface M protein quantity increased after complementation.
Conclusions:
- A defective Mga regulator is responsible for reduced virulence gene expression in this GAS strain.
- Restoring Mga function through genetic complementation re-establishes virulence.
- Mga is essential for regulating GAS virulence in a mouse model.