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Updated: Jan 29, 2026
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Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
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Phase Variation of Streptococcus pneumoniae
1Center for Infectious Disease Research, Department of Basic Medical Science, School of Medicine, Tsinghua University, Beijing 100084, China.
Microbiology Spectrum
|February 10, 2019
Summary
Streptococcus pneumoniae exhibits reversible phase variation in colony opacity, impacting virulence and colonization. This variation is driven by DNA methylation changes in specific genes, allowing adaptation for infection or carriage.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pneumoniae displays phase variation, a reversible phenotypic change affecting traits like colony opacity, capsule production, and pilus expression.
- Colony opacity variation is observed in all strains and is extensively characterized, distinguishing between opaque and transparent colony phenotypes.
Purpose of the Study:
- To elaborate on the phenomenon of colony opacity variation in Streptococcus pneumoniae.
- To detail the distinct metabolic, cellular, and virulence characteristics of opaque and transparent variants.
- To explain the underlying genetic mechanism of pneumococcal opacity variation.
Main Methods:
- Characterization of colony opacity variation in Streptococcus pneumoniae.
- Analysis of differential gene expression and phenotypic traits between opaque and transparent variants.
- Investigation of DNA methylation patterns and genetic inversions in the colony opacity determinant (cod) or SpnD39III locus.
Main Results:
- Opaque variants exhibit higher virulence in sepsis models but poor nasopharyngeal colonization due to increased capsular polysaccharides and decreased teichoic acids.
- Transparent variants show efficient nasopharyngeal colonization but reduced virulence, characterized by fewer capsular polysaccharides and more teichoic acid.
- Pneumococcal opacity variants are generated by differential genome DNA methylation, controlled by DNA inversions in three homologous hsdS genes of a type I restriction-modification system.
Conclusions:
- Phase variation in Streptococcus pneumoniae, specifically colony opacity, is a complex mechanism involving DNA inversion and differential methylation.
- This reversible switch allows for the generation of mixed populations, facilitating adaptation for either host colonization or systemic infection.
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