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Capsulation loci of non-serotype b encapsulated Haemophilus influenzae
C Ogilvie1, A Omikunle, Y Wang
1Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
Abstract:
Invasive infections caused by non-type b encapsulated Haemophilus influenzae have increased recently. Because capsule is a major virulence factor, capsulation of 62 recently isolated non-serotype b encapsulated strains was examined. Repeated serotyping confirmed only 69.0% of isolates. The combination of slide agglutination and cap genotyping confirmed 78.9% of type a, 100% of type e, and 86.4% of type f strains. Seven nonencapsulated strains may have lost capsulation through homologous recombination. Three strains that could not be serotyped or genotyped failed to hybridize with any cap probe and are probably nontypeable H. influenzae. Of isolates that retained an intact cap locus, 62.2% had evidence of cap amplification. The epidemiology of non-type b encapsulated H. influenzae infections is complicated by the poor specificity of available serologic reagents and by spontaneous capsule loss. Recently isolated invasive non-type b encapsulated H. influenzae frequently have cap amplification, which may contribute to their virulence.
Insights
Non-type b encapsulated Haemophilus influenzae infections are rising. Studies show poor serotyping accuracy and spontaneous capsule loss, complicating diagnosis and treatment of these invasive bacterial infections.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Genetics
Background:
- Invasive infections caused by non-type b encapsulated Haemophilus influenzae are increasing.
- Capsular polysaccharide is a key virulence factor in Haemophilus influenzae.
- Accurate identification of encapsulated strains is crucial for understanding disease epidemiology.
Purpose of the Study:
- To examine the capsulation status of recently isolated non-serotype b encapsulated Haemophilus influenzae strains.
- To assess the reliability of current diagnostic methods for these bacteria.
- To investigate potential mechanisms of capsule loss and identify factors contributing to virulence.
Main Methods:
- Serotyping of 62 non-type b encapsulated Haemophilus influenzae isolates.
- Combination of slide agglutination and cap genotyping for strain confirmation.
- Analysis of cap locus integrity and evidence of gene amplification.
Main Results:
- Serotyping confirmed only 69.0% of isolates, highlighting diagnostic limitations.
- Cap genotyping confirmed 78.9% of type a, 100% of type e, and 86.4% of type f strains.
- Seven strains lost capsulation, likely via homologous recombination; three were identified as nontypeable.
- 62.2% of isolates with intact cap loci showed evidence of cap amplification, potentially increasing virulence.
Conclusions:
- The epidemiology of non-type b encapsulated Haemophilus influenzae is complex due to poor serologic reagent specificity and spontaneous capsule loss.
- Recently isolated invasive strains frequently exhibit cap amplification, suggesting a role in enhanced virulence.
- Improved diagnostic and typing methods are needed for accurate assessment of non-type b encapsulated Haemophilus influenzae infections.