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Updated: Mar 23, 2026
Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination
Published on: September 25, 2014
Streptococcus pneumoniae capsule determines disease severity in experimental pneumococcal meningitis
Lucy J Hathaway1, Denis Grandgirard2, Luca G Valente2
1Institute for Infectious Diseases, Faculty of Medicine, University of Bern, Bern 3001, Switzerland lucy.hathaway@ifik.unibe.ch.
Abstract:
Streptococcus pneumoniaebacteria can be characterized into over 90 serotypes according to the composition of their polysaccharide capsules. Some serotypes are common in nasopharyngeal carriage whereas others are associated with invasive disease, but when carriage serotypes do invade disease is often particularly severe. It is unknown whether disease severity is due directly to the capsule type or to other virulence factors. Here, we used a clinical pneumococcal isolate and its capsule-switch mutants to determine the effect of capsule, in isolation from the genetic background, on severity of meningitis in an infant rat model. We found that possession of a capsule was essential for causing meningitis. Serotype 6B caused significantly more mortality than 7F and this correlated with increased capsule thickness in the cerebrospinal fluid (CSF), a stronger inflammatory cytokine response in the CSF and ultimately more cortical brain damage. We conclude that capsule type has a direct effect on meningitis severity. This is an important consideration in the current era of vaccination targeting a subset of capsule types that causes serotype replacement.
Insights
The capsule type of Streptococcus pneumoniae directly impacts meningitis severity. Specific serotypes, like 6B, cause more mortality and brain damage than others, highlighting the importance of capsule type in disease.
Area of Science:
- Microbiology
- Immunology
- Neurology
Background:
- Streptococcus pneumoniae has over 90 serotypes based on polysaccharide capsule composition.
- While some serotypes cause carriage and others invasive disease, the severity of invasive disease by carriage serotypes is unknown.
- The direct contribution of capsule type versus other virulence factors to disease severity remains unclear.
Purpose of the Study:
- To determine the direct effect of pneumococcal capsule type on meningitis severity.
- To isolate the impact of capsule type from other genetic factors using capsule-switch mutants.
- To investigate the role of capsule in the infant rat model of pneumococcal meningitis.
Main Methods:
- Utilized a clinical isolate of Streptococcus pneumoniae and its capsule-switch mutants.
- Inoculated infant rats to establish a meningitis model.
- Assessed mortality, capsule thickness in cerebrospinal fluid (CSF), inflammatory cytokine response in CSF, and cortical brain damage.
Main Results:
- A polysaccharide capsule is essential for Streptococcus pneumoniae to cause meningitis.
- Serotype 6B demonstrated significantly higher mortality rates compared to serotype 7F.
- Increased capsule thickness in CSF, heightened inflammatory cytokine response, and greater cortical brain damage were observed with serotype 6B.
Conclusions:
- Pneumococcal capsule type directly influences the severity of meningitis.
- Capsule characteristics, such as thickness, correlate with disease outcomes.
- Findings are critical for understanding serotype replacement in the context of current vaccination strategies targeting specific capsule types.
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Risk Factors
Various factors influence the likelihood of developing pneumonia. Age plays a crucial role, with infants, children under two, and individuals over 65 at increased risk due to their...