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Updated: Mar 2, 2026
Assessing Respiratory Immune Responses to Haemophilus Influenzae
Published on: June 29, 2021
Flagellar expression in clinical isolates of non-typeable Haemophilus influenzae
Alejandro Carabarin-Lima1, Patricia Lozano-Zarain1, Miguel Castañeda-Lucio1
1Benemérita Universidad Autónoma de Puebla, Instituto de Ciencias, Posgrado en Microbiología, Centro de Investigaciones en Ciencias Microbiológicas, Puebla, México.
Purpose:
Haemophilus influenzae is a commensal organism found in the upper respiratory tract of humans. When H. influenzae becomes a pathogen, these bacteria can move out of their commensal niche and cause multiple respiratory tract diseases such as otitis media, sinusitis, conjunctivitis and bronchitis in children, and chronic obstructive pulmonary disease in adults. However, H. influenzae is currently considered a non-flagellate bacterium.
Methodology And Results:
In this study, 90 clinical isolates of H. influenzae strains (typeable and non-typeable) showed different degrees of the swarm-motility phenotype in vitro.Keys findings. One of these strains, NTHi BUAP96, showed the highest motility rate and its flagella were revealed using transmission electron microscopy and Ryu staining. Moreover, the flagellar genes fliC and flgH exhibited high homology with those of Actinobacillus pleuropneumoniae, Escherichia coli and Shigella flexneri. Furthermore, Western blot analysis, using anti-flagellin heterologous antibodies from E. coli, demonstrated cross-reaction with a protein present in NTHi BUAP96.
Conclusion:
This study provides, for the first time, information on flagellar expression in H. influenzae, representing an important finding related to its evolution and pathogenic potential.
Insights
This study reveals that Haemophilus influenzae possesses flagella, challenging its classification as non-flagellate. This finding is crucial for understanding the bacterium's pathogenic potential and evolution.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
Background:
- Haemophilus influenzae is a common human commensal.
- Pathogenic strains cause significant respiratory infections in children and adults.
- H. influenzae has been historically considered a non-flagellate bacterium.
Purpose of the Study:
- To investigate the presence and characteristics of flagella in Haemophilus influenzae.
- To explore the implications of flagellar expression on bacterial motility and pathogenicity.
Main Methods:
- Analysis of 90 clinical isolates of H. influenzae for swarm-motility phenotype.
- Transmission electron microscopy and Ryu staining to visualize flagella.
- Gene homology analysis of flagellar genes (fliC, flgH).
- Western blot analysis using anti-flagellin antibodies.
Main Results:
- Variable swarm-motility observed across H. influenzae isolates.
- Strain NTHi BUAP96 exhibited high motility, with flagella confirmed by microscopy.
- Flagellar genes showed homology with other motile bacteria.
- Cross-reactivity in Western blot confirmed flagellin presence.
Conclusions:
- This study provides the first evidence of flagellar expression in H. influenzae.
- The presence of flagella may influence the bacterium's pathogenic potential and evolutionary trajectory.
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