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Bacteriophage control of antiphagocytic determinants in group A streptococci
Abstract:
At least two genes have been shown to be required for the expression of the antiphagocytic M protein molecule in group A streptococci. Evidence for phage involvement in the expression of M protein is that: (a) M- cultures of bacteria can be converted to the M+ state (resistant to phagocytosis) upon lysogenization with appropriate bacteriophages; (b) without those bacteriophages the M- recipient culture could not be detected to revert to the M+ state, even under our most stringent selective conditions; and (c) stable M+ lysogens cured of their bacteriophages returned to the M- state. Immunochemical analysis of lysogenically converted M+ strains demonstrated that they contain precipitating and antiphagocytic determinants of the parental M-76 strain (CS110) rather than M-12 determinants expressed by the phage donor strain. This information strongly suggests that the M- strain CS112 possesses the structural gene for M protein, but that it remains predominantly unexpressed. Quantitation of the M antigen produced by these strains supports the observation that the M- phage-recipient strain possesses a small amount of extractable M antigen and that phage activates its synthesis by some unknown mechanism. Various possibilities to account for the phage requirement in M protein synthesis and its role in the transition between M+ and M- states are discussed.
Insights
Bacteriophages activate the expression of M protein in group A streptococci, enabling resistance to phagocytosis. This phage-mediated activation is crucial for the M+ state, with bacteria reverting to M- upon phage removal.
Area of Science:
- Microbiology
- Bacteriology
- Molecular Biology
Background:
- Group A streptococci express antiphagocytic M protein, crucial for virulence.
- The genetic basis for M protein expression and its regulation is not fully understood.
Purpose of the Study:
- To investigate the role of bacteriophages in the expression of M protein in group A streptococci.
- To elucidate the mechanism by which phages influence M protein synthesis and the M+ phenotype.
Main Methods:
- Bacterial lysogenization with specific bacteriophages.
- Phage curing experiments.
- Immunochemical analysis of M protein expression.
- Quantitation of M antigen production.
Main Results:
- Lysogenization of M- streptococci with specific phages converted them to the M+ state.
- M+ strains lysogenized with phages expressed M protein determinants from the original strain, not the phage donor.
- Curing lysogenic phages reverted M+ strains to the M- state.
- Phage-dependent strains produced a small amount of M antigen, suggesting phage activates its synthesis.
Conclusions:
- Bacteriophages play a critical role in the expression of M protein in group A streptococci.
- The M- strain possesses the M protein gene, but its expression is predominantly regulated by phage presence.
- Phage activation of M protein synthesis is a key mechanism for achieving the antiphagocytic M+ phenotype.