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Updated: Aug 30, 2026
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
Using cpsA-cpsB sequence polymorphisms and serotype-/group-specific PCR to predict 51 Streptococcus pneumoniae
Fanrong Kong1, Gwendolyn L Gilbert1
1Centre for Infectious Diseases and Microbiology (CIDM), Institute of Clinical Pathology and Medical Research (ICPMR), Westmead Hospital, Darcy Rd, Westmead, New South Wales, 2145 Australia.
Insights
A new molecular capsular typing (MCT) method accurately predicts most Streptococcus pneumoniae serotypes, aiding invasive pneumococcal disease surveillance. This objective method combines gene sequencing and PCR for enhanced epidemiological studies.
Area of Science:
- Microbiology
- Vaccinology
- Epidemiology
Background:
- Pneumococcal vaccines target common Streptococcus pneumoniae serotypes, necessitating ongoing surveillance of invasive pneumococcal disease.
- Monitoring serotype distribution changes is crucial for public health and vaccine efficacy assessment.
Purpose of the Study:
- To develop and evaluate a molecular capsular typing (MCT) system for Streptococcus pneumoniae.
- To compare the accuracy and efficiency of MCT against conventional serotyping (CS) methods.
Main Methods:
- Developed MCT based on partial cpsA-cpsB gene sequencing and serotype-specific PCR targeting wzy and wzx genes.
- Evaluated MCT using 151 S. pneumoniae isolates of known serotype and 276 recent clinical isolates (total 427).
- Analyzed 376 heterogeneity sites in the cpsA-cpsB region to identify sequence types (STs).
Main Results:
- Identified 89 sequence types (STs), with 76 corresponding to single serotypes and 11 containing mixed serotypes.
- MCT accurately predicted serotypes for most isolates, with limited conventional serotyping (CS) needed for 22% of isolates with mixed STs.
- Serotype 23F-specific PCR resolved ambiguities in two mixed STs.
Conclusions:
- Molecular capsular typing (MCT) is a specific, objective, and practical method for predicting S. pneumoniae serotypes.
- MCT facilitates epidemiological studies of invasive pneumococcal disease.
- Further research is needed to refine MCT and understand its relationship with CS for improved serotype differentiation.
Abstract:
Streptococcus pneumoniae polysaccharide and protein-conjugate vaccines are available against the most commonly isolated pneumococcal serotypes. Ongoing surveillance of invasive pneumococcal disease is needed in order to monitor changes in distribution of serotypes. Based on previously published sequences of capsular polysaccharide synthesis (cps) gene clusters of 16 pneumococcal serotypes, a molecular capsular typing (MCT) system has been developed, based on a combination of partial cpsA-cpsB sequencing and serotype- or serogroup-specific PCR, targeting the genes wzy and wzx (except for serotype 3). In this study, 151 S. pneumoniae isolates of known serotype (representing 51 serotypes) and 276 recent clinical isolates were used to develop MCT and compare it with conventional serotyping (CS) (total 427 isolates). On the basis of 376 heterogeneity sites in the cpsA-cpsB region, 89 sequence types (ST) were identified, of which 76 corresponded to a single serotype and 11 contained two serotypes. The correct serotypes in two of the latter (10A-23F-g and 23F-23A) were identified using serotype 23F-specific PCR. Limited CS was required for 92 (22 %) isolates to distinguish between the two serotypes in the nine other mixed ST (6A-6B-g, 6A-6B-q, 15B-22F, 33F-33A, 17F-35B, 18B-18C, 13-20, 25F-38, 31-42). MCT is a specific, objective and practical method that can predict the serotype of most S. pneumoniae isolates; it will facilitate epidemiological studies. Further study of the relationship between MCT and CS is needed in order to improve our understanding of serotype differentiation and to improve MCT methods further.
