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Haemophilus parasuis comprises strains of different virulence, but the virulence factors of this bacterium are not well defined. CReSA’s researchers have found that H. aemophilus 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.
A neuraminidase activity has been previously detected in H. parasuis, but the role of sialylation in the virulence of this bacterium has not been studied. To explore the relationship between sialic acid (Neu5Ac) and virulence, we assessed the distribution of genes involved in sialic acid metabolism in 21 H. parasuis strains from different clinical origins (including nasal and systemic isolates). The neuraminidase gene nanH, together with CMP-Neu5Ac synthetase and sialyltransferase genes neuA, siaB and lsgB, were included in the study. Neuraminidase activity was found to be common in H. parasuis isolates, and the nanH gene from 12 isolates was expressed in Escherichia coli and further characterized. Sequence analysis showed that the NanH predicted protein contained the motifs characteristic of the catalytic site of sialidases. While an association between the presence of nanH and the different origins of the strains was not detected, the lsgB gene was predominantly present in the systemic isolates, and was not amplified from any of the nasal isolates tested. Analysis of the lipooligosaccharide (LOS) from reference strains Nagasaki (virulent, lsgB+) and SW114 (non-virulent, lsgB−) showed the presence of sialic acid in the LOS from the Nagasaki strain, supporting the role of sialylation in the virulence of this bacterial pathogen. Further studies are needed to clarify the role of sialic acid in the pathogenicity of H. parasuis.
V. Martínez-Moliner, P. Soler-Llorens, J. Moleres, J. Garmendia and V. Aragon. Distribution of genes involved in sialic acid utilization in strains of Haemophilus parasuis. Microbiology. 2012. Vol. 158 (8), 2117-2124. doi:10.1099/mic.0.056994-0