A new discovery in the virulence mechanisms of the porcine pathogen Haemophilus parasuis

CReSA’s researchers have found that Haemophilus parasuis can utilize the sialic acid from the host to avoid recognition by the immune system and be able to cause disease. In addition, a gene associated with the virulence of the bacterial strain has been identified. This gene could be useful in the diagnosis of virulent strains of H. parasuis.

Haemophilus parasuis is a swine respiratory pathogen that produces economical losses in all countries with porcine production. This bacterium can be found in the nasal cavity of healthy pigs, where does not produce clinical disease; but virulent strains can produce Glässer’s disease. Glässer’s disease appears in farms under certain circumstances and it is characterized by a systemic inflammation that can involve the nervous system and produce meningitis. The identification of virulence factors to differentiate virulent from non-virulent colonizing strains, and the understanding of the pathogenesis of the disease caused by this bacterium have been the focus of several research studies at CReSA.

The use of sialic acid from the host by bacteria is a well known phenomenon. Thus, bacteria can use this sialic acid as nutrient or to decorate their surface in order to avoid recognition by the host immune system. In order to utilize sialic acid, bacteria need to have several enzymes, including:
- Neuraminidase, to release sialic acid from complex molecules from the host.
- Sialyltransferase, to transfer the released sialic acid to the lipopolysaccharide on the bacterial surface.

Previous studies in H. parasuis found a neuraminidase activity in the bacterium, but the distribution of this activity in strains of different clinical origin was not determined and the corresponding gene was not identified. In this work, we have identified the gene responsible for the neuraminidase activity and found that is widely distributed in H. parasuis strains, independently of the virulence. Besides, a sialyltransferase gene was detected, and this gene was associated with the virulence of the strains, and more specifically with the resistance to the bactericidal effect of serum (serum or complement resistance). Using two reference strains, we demonstrated that the lipopolysaccharide in the virulent strain (serum resistant) was decorated with sialic acid.

These results support that H. parasuis, as well as other bacteria from the same family, is able to use the sialic acid from the pig to avoid recognition by the immune system and cause disease. These results provide new information to understand how H. parasuis can produce disease and to differentiate strains depending on their virulence. This information can assist in the future to control Glässer’s disease.

These results have been published recently in: Distribution of genes involved in sialic acid utilization in strains of Haemophilus parasuis. Verónica Martínez-Moliner, Pedro Soler-Llorens, Javier Moleres, Junkal Garmendia and Virginia Aragon. Microbiology (2012), 158, 2117–2124. The study, leaded by Dr. Aragón from CReSA-IRTA in collaboration with Dr. Garmendia from Instituto Agrobiotecnologıía of Navarra (UPNA-CSIC-Gobierno Navarra), has counted with the participation of the Department of Microbiology and Parasitology from the Universidad de Navarra.

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If you want to contact with the author of this article:

Dr Virginia Aragón Fernández
Researcher from the Research Line of Respiratory bacterial infections
Subprogram Bacterial and endoparasitic infections, and antimicrobial resistance
Correo electrónico: virginia.aragon@cresa.uab.cat
Teléfono: +34 93 581 44 94
Fax: +34 93 581 44 90
Edifici CReSA. Campus UAB
08193 Bellaterra (Barcelona) Spain

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