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Updated: Feb 18, 2026
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
PCR-based discrimination of emerging Streptococcus pneumoniae serotypes 22F and 33F
Hayley D Gillis1, Walter H B Demczuk2, Averil Griffith2
1Canadian Center for Vaccinology (CCfV), Dalhousie University, Halifax, Nova Scotia (NS), Canada; Nova Scotia Health Authority (NSHA), Halifax, Nova Scotia (NS), Canada.
Abstract:
Serotyping of Streptococcus pneumoniae is important to monitor disease epidemiology and assess the impact of pneumococcal vaccines. Traditionally, the Quellung reaction used serotype-specific antibodies to classify S. pneumoniae based on differences in capsular antigens. More recently, PCR-based serotype deduction relying on serotype-specific capsule biosynthesis genes has been broadly applied for pneumococcal surveillance. However, PCR-based serotyping lacks discrimination for certain S. pneumoniae serotypes, including the differentiation of serotype 22F from 22A, and serotype 33F from 33A and 37. Serotypes 22F and 33F are emerging serotypes that are absent in the currently licensed 13-valent pneumococcal conjugate vaccine, but present in the new candidate 15-valent formulation. This study validated novel PCR reactions to detect and discriminate S. pneumoniae serotypes 22F and 33F. In order to differentiate S. pneumoniae serotypes 22F or 33F from genetically similar serotypes, two novel PCR reactions were designed and validated. The specificity of all PCR targets was evaluated using all 92 different S. pneumoniae serotypes, as well as 32 other streptococci. Reproducibility was evaluated using geographically and genetically diverse strains of S. pneumoniae serotypes 22F and 22A, or serotypes 33F, 33A, and 37 that were previously characterized by reputable reference laboratories. Overall, S. pneumoniae serotypes 22F and 33F could be accurately and reproducibly be detected and discriminated using PCR alone. Such a molecular serotyping approach provides a valuable diagnostic tool that is feasible in any molecular laboratory, to enable pneumococcal serotype surveillance and subsequent assessment of the impact of the new 15-valent candidate pneumococcal vaccine.
Insights
Novel PCR methods accurately identify emerging Streptococcus pneumoniae serotypes 22F and 33F, crucial for monitoring vaccine impact. This molecular serotyping tool aids global pneumococcal surveillance and vaccine development.
Area of Science:
- Microbiology
- Molecular Biology
- Vaccinology
Background:
- Accurate serotyping of Streptococcus pneumoniae is vital for disease epidemiology and pneumococcal vaccine impact assessment.
- Traditional Quellung reactions and current PCR methods have limitations in discriminating specific pneumococcal serotypes, including 22F/22A and 33F/33A/37.
- Emerging serotypes 22F and 33F are relevant to new 15-valent pneumococcal conjugate vaccine candidates.
Purpose of the Study:
- To validate novel PCR reactions for the accurate detection and discrimination of Streptococcus pneumoniae serotypes 22F and 33F.
- To differentiate these emerging serotypes from genetically similar ones.
- To provide a molecular tool for enhanced pneumococcal serotype surveillance.
Main Methods:
- Design and validation of two novel PCR reactions targeting specific capsule biosynthesis genes.
- Evaluation of PCR target specificity against all 92 S. pneumoniae serotypes and 32 other streptococci.
- Assessment of reproducibility using diverse geographical and genetic strains of S. pneumoniae serotypes 22F/22A and 33F/33A/37.
Main Results:
- The novel PCR assays accurately and reproducibly detected and discriminated Streptococcus pneumoniae serotypes 22F and 33F.
- High specificity was confirmed against a comprehensive panel of S. pneumoniae serotypes and related streptococci.
- The molecular approach demonstrated reliable differentiation from closely related serotypes.
Conclusions:
- Novel PCR reactions provide an accurate and reproducible method for molecular serotyping of S. pneumoniae serotypes 22F and 33F.
- This diagnostic tool is feasible for molecular laboratories, supporting enhanced pneumococcal serotype surveillance.
- The validated method will aid in assessing the impact of new pneumococcal vaccines, including the 15-valent candidate.
