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Role of M protein in pharyngeal colonization by group A streptococci in rats
S K Hollingshead1, J W Simecka, S M Michalek
1Department of Microbiology, University of Alabama, Birmingham 35294.
Abstract:
As the initial step in infection, group A streptococci (GAS) colonize either the nasopharyngeal mucosa or the skin of humans. A number of virulence factors have been implicated in the colonization phase of pathogenesis based upon their in vitro activities, but the in vivo data supporting their role in colonization of the host tissues is lacking. In this investigation, the potential requirement for M protein in pharyngeal colonization by GAS was explored by using near-isogenic strains in experimental animals studies. Fischer rats were infected by intranasal and oral inoculation with both M-positive and M-negative Streptococcus pyogenes strains. Colonization of the pharyngeal area by the streptococci was monitored at various time intervals. Both M-positive and M-negative strains colonized during the first week following infection, indicating that M protein was not necessary for this initial colonization. Two M-positive strains of S. pyogenes were recovered from the rats up to 23 weeks following inoculation, while the colonization levels for M-negative strains decreased rapidly in the second and third weeks, becoming negligible by the fourth week. This indicates a potential role for M protein in the persistence of colonization at this mucosal surface. Colonization of rats with either M-positive strain of S. pyogenes also resulted in the appearance of salivary and serum antibody responses. This in vivo model should allow further investigation into factors required for GAS disease, including the examination of the potential role of the host immune response both in modulation of the pharyngeal surface and in modulation of antigenic changes in M protein or other surface factors.
Insights
Group A Streptococcus M protein is not essential for initial pharyngeal colonization but is crucial for long-term persistence. This study highlights M protein's role in maintaining GAS infections in vivo.
Area of Science:
- Microbiology
- Infectious Diseases
- Immunology
Background:
- Group A Streptococcus (GAS) colonization is the first step in infection.
- In vitro studies suggest GAS virulence factors aid colonization, but in vivo data is limited.
- The role of M protein in GAS pharyngeal colonization requires further in vivo investigation.
Purpose of the Study:
- To investigate the role of M protein in the initial and persistent pharyngeal colonization by GAS.
- To evaluate the host immune response to GAS colonization in an animal model.
- To establish an in vivo model for studying GAS pathogenesis.
Main Methods:
- Experimental animal studies using Fischer rats.
- Intranasal and oral inoculation with M-positive and M-negative Streptococcus pyogenes strains.
- Monitoring of pharyngeal colonization at various time intervals and assessment of antibody responses.
Main Results:
- Both M-positive and M-negative GAS strains initially colonized the pharynx.
- M-positive strains demonstrated persistence up to 23 weeks, while M-negative strains showed rapid decline after week 3.
- GAS colonization elicited salivary and serum antibody responses in rats.
Conclusions:
- M protein is not required for the initial colonization of the rat pharynx by GAS.
- M protein plays a significant role in the persistence of GAS colonization at mucosal surfaces.
- The developed in vivo model facilitates further research into GAS virulence factors and host immune responses.