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Updated: Jan 31, 2026
Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination
Published on: September 25, 2014
Streptococcus mitis Expressing Pneumococcal Serotype 1 Capsule
Fernanda C Lessa1, Jennifer Milucky2, Nadine G Rouphael3
1Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases, Division of Bacterial Diseases, Atlanta, Georgia, USA. flessa@cdc.gov.
Abstract:
Streptococcus pneumoniae's polysaccharide capsule is an important virulence factor; vaccine-induced immunity to specific capsular polysaccharide effectively prevents disease. Serotype 1 S. pneumoniae is rarely found in healthy persons, but is highly invasive and a common cause of meningitis outbreaks and invasive disease outside of the United States. Here we show that genes for polysaccharide capsule similar to those expressed by pneumococci were commonly detected by polymerase chain reaction among upper respiratory tract samples from older US adults not carrying pneumococci. Serotype 1-specific genes were predominantly detected. In five oropharyngeal samples tested, serotype 1 gene belonging to S. mitis expressed capsules immunologically indistinct from pneumococcal capsules. Whole genome sequencing revealed three distinct S. mitis clones, each representing a cps1 operon highly similar to the pneumococcal cps1 reference operon. These findings raise important questions about the contribution of commensal streptococci to natural immunity against pneumococci, a leading cause of mortality worldwide.
Insights
Genes for Streptococcus pneumoniae
Area of Science:
- Microbiology
- Immunology
- Genetics
Background:
- The polysaccharide capsule of Streptococcus pneumoniae is a key virulence factor.
- Vaccine-induced immunity targeting specific capsular polysaccharides prevents pneumococcal disease.
- Serotype 1 Streptococcus pneumoniae is highly invasive and associated with meningitis outbreaks.
Purpose of the Study:
- To investigate the presence and characteristics of Streptococcus pneumoniae-like polysaccharide capsule genes in commensal bacteria.
- To explore the immunological similarity of capsules expressed by commensal streptococci to those of Streptococcus pneumoniae.
- To understand the genetic relatedness of commensal bacteria expressing these capsule genes.
Main Methods:
- Polymerase chain reaction (PCR) was used to detect specific genes in upper respiratory tract samples.
- Oropharyngeal samples were analyzed for the presence and immunological properties of expressed capsules.
- Whole genome sequencing was performed on identified bacterial clones.
Main Results:
- Genes for polysaccharide capsules similar to those of Streptococcus pneumoniae were frequently detected in adults not carrying pneumococci.
- Serotype 1-specific genes were predominantly found.
- Capsules expressed by serotype 1 genes in Streptococcus mitis were immunologically indistinguishable from pneumococcal capsules.
- Whole genome sequencing identified three distinct Streptococcus mitis clones with cps1 operons highly similar to the pneumococcal reference.
Conclusions:
- Commensal streptococci, such as Streptococcus mitis, can harbor genes for Streptococcus pneumoniae-like capsules.
- These findings suggest a potential role for commensal streptococci in natural immunity against Streptococcus pneumoniae.
- Further research is needed to elucidate the contribution of commensal bacteria to immunity against pneumococcal infections.
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