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Updated: Jul 14, 2026
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
Real-time PCR for determining capsular serotypes of Haemophilus influenzae
Younes Maaroufi1, Jean-Marc De Bruyne, Corine Heymans
1Department of Microbiology and Infectious Diseases, Institut Jules Bordet, Rue Héger-Bordet 1, 1000 Brussels, Belgium.
Abstract:
A two-step real-time PCR assay targeting all six capsulation loci of Haemophilus influenzae (i.e., serotypes a to f) was developed and compared with a previously published qualitative PCR assay by using 131 H. influenzae clinical isolates. There was a 98.5% concordance between the two tests. The sensitivity of detection of capsular type-specific reference strains of H. influenzae a to c (10(1) CFU/PCR) was higher than that for type e (10(3) CFU/PCR) and types d and f (10(4) CFU/PCR), and a broader dynamic range was obtained (5 to 8 log(10) units). No cross-reaction was observed with bacteria commonly isolated from the respiratory tract. We showed that both PCR assays are more reliable than slide agglutination serotyping. The real-time PCR-based assay seems to be an alternative of choice for the epidemiological follow-up of H. influenzae invasive infections.
Insights
A new real-time PCR assay accurately identifies all six Haemophilus influenzae capsular types (a-f). This method offers improved sensitivity and reliability for tracking invasive infections compared to older techniques.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Haemophilus influenzae causes invasive infections.
- Accurate serotyping is crucial for epidemiological tracking.
- Existing methods like slide agglutination have limitations.
Purpose of the Study:
- To develop and evaluate a two-step real-time PCR assay for identifying all six capsular types (a-f) of Haemophilus influenzae.
- To compare the performance of the real-time PCR assay against a qualitative PCR assay and slide agglutination serotyping.
Main Methods:
- Development of a two-step real-time PCR assay targeting capsulation loci.
- Testing the assay with 131 clinical isolates of Haemophilus influenzae.
- Comparison with a previously published qualitative PCR assay and slide agglutination.
Main Results:
- High concordance (98.5%) between the real-time PCR and qualitative PCR assays.
- Real-time PCR demonstrated superior sensitivity for serotypes a-c and a broader dynamic range.
- No cross-reactivity with common respiratory tract bacteria was observed.
- Both PCR assays were found to be more reliable than slide agglutination serotyping.
Conclusions:
- The developed real-time PCR assay is a reliable and sensitive tool for identifying Haemophilus influenzae serotypes.
- This assay is a valuable alternative for the epidemiological surveillance of invasive Haemophilus influenzae infections.
