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Expression of capsules by Haemophilus influenzae in mixed infections
1Naval Medical Research Institute, Bethesda, Maryland, USA.
Abstract:
The pathogenicity of eight clinical isolates of non-type b Haemophilus influenzae was investigated by inoculating them subcutaneously into mice, alone or mixed with viable or non-viable bacteria of certain other species. Three of the H. influenzae isolates were non-capsulated while five were slightly capsulated (less than 1% of organisms had capsules). The other strains of bacteria tested were four isolates of capsulated and four isolates of non-capsulated pigmented strains of Prevotella sp. and Porphyromonus sp. as well as a capsulate Klebsiella pneumoniae ("helpers"). None of the non-capsulated strains induced an abscess when inoculated alone. Following co-inoculation of viable or non-viable "helpers" with H. influenzae, abscesses were formed in all instances in which the "helper" had a capsule. Profusely capsulated cells of H. influenzae were recovered, however, only from abscesses induced with the five slightly capsulated strains of H. influenzae. These capsulated organisms were found serologically to be of type b and induced abscesses when inoculated alone. Our findings illustrate the ability of non-capsulated strains of H. influenzae to produce progeny of capsulated type b organisms after co-inoculation with certain other species.
Insights
Non-encapsulated Haemophilus influenzae can become encapsulated type b strains when co-inoculated with helper bacteria. This study reveals how non-type b H. influenzae can transform into pathogenic type b strains.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Haemophilus influenzae is a significant human pathogen.
- Non-type b strains are generally less virulent than type b strains.
- The capsular polysaccharide is a key virulence factor for H. influenzae.
Purpose of the Study:
- To investigate the pathogenicity of non-type b Haemophilus influenzae clinical isolates.
- To determine if non-type b H. influenzae can acquire capsulation and pathogenicity.
- To explore the role of other bacterial species in H. influenzae transformation.
Main Methods:
- Subcutaneous inoculation of mice with H. influenzae isolates, alone or with "helper" bacteria.
- Assessment of abscess formation and bacterial recovery.
- Serological analysis of recovered H. influenzae strains.
Main Results:
- Non-encapsulated H. influenzae did not induce abscesses alone.
- Co-inoculation with encapsulated "helper" bacteria (Klebsiella pneumoniae, Prevotella sp., Porphyromonas sp.) led to abscess formation.
- Slightly capsulated H. influenzae strains, when co-inoculated, yielded profusely capsulated type b organisms.
- Recovered type b H. influenzae strains were pathogenic independently.
Conclusions:
- Non-encapsulated H. influenzae strains can acquire a capsule and become pathogenic type b strains.
- Co-infection with encapsulated bacteria facilitates the transformation of H. influenzae.
- This mechanism highlights a potential pathway for the emergence of virulent H. influenzae type b.