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Relationship of M protein genes in group A streptococci
Abstract:
The M protein of group A streptococci is considered one of the primary virulence determinants of this organism because it prevents phagocytosis. All of the 56 different M protein types of group A streptococci tested contain a DNA region that hybridizes with a labeled probe consisting of DNA encoding the type 6 M protein (emm6 gene). In addition, 2 of 3 functionally M- group A strains (strains that are successfully phagocytized) also contain this gene, but this DNA is not present in 1 M- strain. Of the other streptococcal groups, only groups C and G, which are closely related to group A, contain DNA that hybridizes with emm6. None of the non-streptococcal Gram-positive bacteria tested contains emm6-related DNA. In the strain from which emm6 was cloned, there appears to be only a single copy of this gene.
Insights
The M protein gene (emm6) is present in most Group A Streptococcus strains, aiding in virulence by preventing phagocytosis. This gene is also found in related Groups C and G streptococci, but not in non-streptococcal bacteria.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Group A Streptococcus (GAS) is a significant human pathogen.
- The M protein is a key virulence factor in GAS, inhibiting phagocytosis.
- Understanding the genetic basis of M protein is crucial for combating GAS infections.
Purpose of the Study:
- To investigate the presence and distribution of the M protein gene (emm6) in various streptococcal groups.
- To determine the correlation between emm6 gene presence and M protein-mediated virulence in GAS.
Main Methods:
- DNA hybridization techniques were used to detect the emm6 gene.
- A labeled DNA probe encoding the type 6 M protein (emm6) was employed.
- Various strains of Group A, C, and G streptococci, as well as non-streptococcal bacteria, were tested.
Main Results:
- The emm6 gene was detected in all tested Group A Streptococcus strains, regardless of M protein type.
- Two of three M-negative (phagocytized) GAS strains contained the emm6 gene, while one lacked it.
- DNA hybridization with emm6 was positive for closely related Group C and G streptococci, but negative for all tested non-streptococcal Gram-positive bacteria.
- A single copy of the emm6 gene was observed in the strain from which it was cloned.
Conclusions:
- The emm6 gene is a common genetic element in Group A Streptococcus and is present in related streptococcal groups.
- The presence of the emm6 gene is strongly associated with M protein virulence, although exceptions exist.
- The emm6 gene is specific to certain streptococcal groups, suggesting its role in their distinct pathogenic profiles.