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A collaborative study between researchers of CReSA (Barcelona), the Department of Veterinary Medicine of the University of Cambridge (UK) and other European research groups has identified the DNA sequences of Haemophilus parasuis responsible for the bacterial capsule production.
Polysaccharides composing the capsule are potential virulence factors of this bacterium. H. parasuis strains are classified in 15 serovars that are differenced by several characteristics, including virulence. Sequences of the 15 reference strains have been identified and characterized and specific sequences among the genes encoding the capsule of each serovar have been detected in this study.
The researchers contend that these loci contain genes for polysaccharide capsule structures, and not a lipopolysaccharide O antigen, supported by the fact that they contain genes such as wza, wzb, and wzc, which are associated with the export of polysaccharide capsules in the current capsule classification system. A conserved region at the 3′ end of the locus, containing the wza, ptp, wzs, and iscR genes, is consistent with the characteristic export region 1 of the model group 1 capsule locus. A potential serovar-specific region (region 2) has been found by comparing the predicted coding sequences (CDSs) in all 15 loci for synteny and homology. The region is unique to each reference strain with the exception of those in serovars 5 and 12, which are identical in terms of gene content.
This finding is a first step towards understanding the basis of strain antigenic specificity and opens new possibilities for the developing of molecular serotyping systems, which could assist in the diagnosis and control of the disease.
Howell KJ, Weinert LA, Luan SL, Peters SE, Chaudhuri RR, Harris D, Angen O, Aragon V, Parkhill J, Langford PR, Rycroft AN, Wren BW, Tucker AW, Maskell DJ; BRaDP1T Consortium. Gene content and diversity of the loci encoding biosynthesis of capsular polysaccharides of the 15 serovar reference strains of Haemophilus parasuis. J Bacteriol. 2013 Sep;195(18):4264-73.