Distribution of genes involved in sialic acid utilization in strains of Haemophilus parasuis

Abstract

Haemophilus parasuis is a porcine respiratory pathogen, well known as the aetiological agent of Glä sser's disease. H. parasuis comprises strains of different virulence, but the virulence factors of this bacterium are not well defined. 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 CMPNeu5Ac 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.

Gene Content and Diversity of the Loci Encoding Biosynthesis of Capsular Polysaccharides of the 15 Serovar Reference Strains of Haemophilus parasuis

“…In fact, the presence of the wza gene and homologues of wzb and wzc (ptp and wzs, respectively) strongly indicates that the locus is required for the biosynthesis of a polysaccharide capsule, rather than an O antigen (33,38,39). Furthermore, experimental evidence does not support the production of an O antigen in H. parasuis (23)(24)(25)40). We therefore propose that this is a capsular polysaccharide biosynthesis locus.…”

“…While there are differences between the two serotyping methods, there is strong evidence that the important antigens in both protocols are polysaccharides. The study of these polysaccharide components in relation to serovar has only just started with the publication of structures of the capsular polysaccharide and LPS for two reference strains, and their expression has been monitored in only a selection of the reference strains (23)(24)(25)(26). There are some problems with the serotyping assay, including the difficulty of consistently producing specific antisera against several reference strains, variation in growth conditions, cross-reactions between serovars, and the very small number of laboratories that currently perform this test (8,18,20,26).…”

Haemophilus parasuis α-2,3-sialyltransferase-mediated lipooligosaccharide sialylation contributes to bacterial pathogenicity

“…LOS is important in host cell adhesion and invasion, which is an important mechanism for H. parasuis infection [30]. Also, the lsgB gene is reported to be present predominantly in systemic clinical isolates but not in nasal isolates [17], indicating a potential relationship in H. parasuis strains between the lsgB gene and adhesion or invasion. The ΔlsgB mutant exhibited significantly attenuated invasion of both PIEC and PK15 cells; however, unexpectedly; we observed a prominent and significant increase in the adhesion of the ΔlsgB mutant to both cell types.…”

“…The genes involved in sialic acid metabolism have been investigated in 21  H. parasuis strains from different clinical origins (including nasal and systemic isolates). These genes include the neuraminidase gene nanH , the CMPNeu5Ac synthetase, and the sialyltransferase genes neuA, siaB and lsgB [17]. Commonly, the sialyltransferase has been classified into α-2,3-sialyltransferase, α-2,6-sialyltransferase and α-2,8-sialyltransferase [18].…”

“…The α-2,3-sialyltransferase encoded by H. parasuis lsgB gene has been grouped into GT38 family [20]. This lsgB gene was predominantly present in the systemic H. parasuis isolates but was not present in any of the nasal isolates [17], suggesting that lsgB -mediated sialylation is likely to affect bacterial pathogenicity. However, the influence of sialylation in H. parasuis pathogenicity is not clear and its mechanism of action remains to be determined.…”