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Surface-associated filamentous hemagglutinin induces autoagglutination of Bordetella pertussis
F D Menozzi1, P E Boucher, G Riveau
1Laboratoire de Microbiologie Génétique et Moléculaire, INSERM CJF 9109, Institut Pasteur, Lille, France.
Abstract:
Filamentous hemagglutinin (FHA) is a major adhesin produced by Bordetella pertussis, the etiologic agent of whooping cough. FHA has been shown to be surface associated but is also secreted by virulent bacteria. Microscopic observations of lungs of mice infected with B. pertussis showed that the bacteria grow as clusters within the alveolar lumen. When B. pertussis was cultivated in vitro with chemically defined medium, bacteria grew as aggregates, mimicking growth observed in vivo. This aggregation was abolished by the addition of cyclodextrin (CDX) to the growth medium and depended on the production of FHA, because a mutant lacking the FHA structural gene failed to form aggregates in a CDX-free medium. Western blot (immunoblot) analyses revealed that, in the absence of CDX, FHA was attached to the bacterial surface and was not efficiently released into the growth medium. Hydrophobic chromatography of FHA showed that CDX drastically reduced the hydrophobicity of FHA, suggesting a direct binding of CDX to FHA, which was further supported by the partial protection of FHA from trypsin digestion in the presence of CDX. In addition, free FHA can interact in a CDX-inhibitable manner with solid phase-immobilized FHA. It can therefore be postulated that the B. pertussis aggregates are most likely due to direct FHA-FHA interaction.
Insights
Filamentous hemagglutinin (FHA) from Bordetella pertussis causes bacterial aggregation. Cyclodextrin (CDX) disrupts this FHA-mediated clumping by reducing FHA hydrophobicity and inhibiting FHA-FHA interactions.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Interactions
Background:
- Bordetella pertussis causes whooping cough and forms aggregates in host lungs.
- Filamentous hemagglutinin (FHA) is a key adhesin involved in B. pertussis virulence.
- B. pertussis aggregates in vitro, mimicking in vivo growth patterns.
Purpose of the Study:
- To investigate the mechanism of B. pertussis aggregation.
- To determine the role of FHA in bacterial aggregation.
- To explore the effect of cyclodextrin (CDX) on FHA-mediated aggregation.
Main Methods:
- In vitro bacterial culture with and without CDX.
- Genetic manipulation of B. pertussis (FHA mutant).
- Western blot analysis.
- Hydrophobic chromatography of FHA.
- Trypsin digestion assay.
- Solid-phase FHA interaction assays.
Main Results:
- B. pertussis forms aggregates in vitro, dependent on FHA production.
- Cyclodextrin (CDX) abolishes B. pertussis aggregation.
- CDX reduces FHA hydrophobicity and inhibits FHA-FHA interactions.
- FHA remains surface-associated and is not efficiently secreted in the absence of CDX.
Conclusions:
- B. pertussis aggregation is mediated by direct FHA-FHA interactions.
- CDX disrupts aggregation by directly binding to FHA, reducing its hydrophobicity.
- Understanding FHA-FHA interactions offers potential therapeutic targets for whooping cough.