Phagocytosis resistance is a virulence mechanism of Haemophilus parasuis

Researchers of CReSA have reported for the first time that phagocytosis resistance is a virulence mechanism of Haemophilus parasuis (H. parasuis) and that several factors may be involved in this function. The paper, published in Veterinary Research describes that H. parasuis strains from different clinical origin present different susceptibility to phagocytosis by porcine alveolar macrophages (PAM).

H. parasuis is a colonizer of the upper respiratory tract of healthy pigs, but virulent strains can cause a systemic infection characterized by fibrinous polyserositis, commonly known as Glässer's disease.

The variability in virulence that is observed among H. parasuis strains is not completely understood, since the virulence mechanisms of H. parasuis are largely unknown. However, it is known that in the course of infection, H. parasuis has to survive the host pulmonary defences, which include alveolar macrophages, to produce disease.

Since resistance to phagocytosis is a common trait of virulent Pasteurellaceae, the aim of this study was to determine if resistance to phagocytosis is also a virulence mechanism of H. parasuis.

Using strains from different clinical backgrounds, we were able to detect clear differences in susceptibility to phagocytosis. Strains isolated from the nose of healthy animals were efficiently phagocytosed by porcine alveolar macrophages (PAM), while strains isolated from systemic lesions were resistant to this interaction. Phagocytosis of susceptible strains proceeded through mechanisms independent of a specific receptor, which involved actin filaments and microtubules.

Confocal images showing the association of virulent (ER6-P and PC4-6P) and non-virulent (SW114) strains with PAM. The green signals correspond to FITC-labelled H. parasuis. PAM were stained with rhodamine-phalloidin (red) to label the cytoplasm and the nuclei were counterstained with DAPI (blue). Z stack images from two independent experiments were captured. Scale bar, 2 μm.

In all the systemic strains tested in this study, we observed a distinct capsule after interaction with PAM, indicating a role of this surface structure in phagocytosis resistance. However, additional mechanisms of resistance to phagocytosis should be explored, since we detected different effects of microtubule inhibition among systemic strains.

This work will contribute to a better understanding of the pathogenesis of H. parasuis helping in the development of better vaccines and diagnostics methods.

These results have been published as Differences in phagocytosis susceptibility in Haemophilus parasuis strains. Olvera A, Ballester M, Nofrarias M, Sibila M, Aragon V. Vet Res. 2009 May-Jun;40(3):24.

To consult the full paper:

To contact with the author of this paper:

Dr. Alexandre Olvera Van Der Stoep
Investigator of the CReSA
Bacterial Diseases Unit
Telephone: +34 93 581 45 67
Fax: +34 93 581 44 90
Edifici CReSA. Campus UAB
08193 Bellaterra (Barcelona) España


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