Molecular analysis of the pathogenicity of Streptococcus pneumoniae: the role of pneumococcal proteins
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J C Paton1, P W Andrew, G J Boulnois
1Department of Microbiology, Adelaide Children's Hospital, Australia.
Abstract:
For many years the virulence of Streptococcus pneumoniae has largely been attributed to its antiphagocytic polysaccharide capsule. Recent evidence, however, indicates that certain pneumococcal proteins play an important part in the pathogenesis of disease, either as mediators of inflammation or by directly attacking host tissues. Pneumococci carrying defined mutations in the genes encoding any one of at least three pneumococcal proteins (the toxin pneumolysin, the major pneumococcal autolysin, and pneumococcal surface protein A) have significantly reduced virulence. Pneumococcal hydrolytic enzymes, such as neuraminidase, hyaluronidase, and IgA1 protease may also contribute to colonization and/or invasion of the host. Several of these proteins (or their detoxified derivatives) are protective immunogens in animal models and therefore warrant consideration for inclusion in human antipneumococcal vaccine formulations.
Insights
Streptococcus pneumoniae virulence is linked to both its capsule and specific proteins like pneumolysin. These proteins, and hydrolytic enzymes, are key to disease and potential vaccine targets.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Historically, Streptococcus pneumoniae virulence was attributed to its antiphagocytic polysaccharide capsule.
- Emerging research highlights the significant role of pneumococcal proteins in disease pathogenesis.
- These proteins can mediate inflammation or directly damage host tissues.
Purpose of the Study:
- To investigate the role of specific pneumococcal proteins in virulence.
- To identify potential vaccine candidates based on pneumococcal proteins and enzymes.
Main Methods:
- Analysis of Streptococcus pneumoniae strains with defined mutations in genes encoding key proteins (pneumolysin, autolysin, pneumococcal surface protein A).
- Evaluation of the contribution of pneumococcal hydrolytic enzymes (neuraminidase, hyaluronidase, IgA1 protease) to colonization and invasion.
- Assessment of the immunogenicity of these proteins and their derivatives in animal models.
Main Results:
- Mutations in pneumolysin, autolysin, or pneumococcal surface protein A genes significantly reduced pneumococcal virulence.
- Pneumococcal hydrolytic enzymes may facilitate host colonization and invasion.
- Several pneumococcal proteins and their detoxified forms demonstrated protective immunogenicity in animal studies.
Conclusions:
- Pneumococcal proteins are critical virulence factors, alongside the capsule.
- Certain pneumococcal proteins and enzymes are promising candidates for novel antipneumococcal vaccines.
- Further research into these protein-based immunogens could lead to improved vaccine formulations.