Abstract
BackgroundStreptococcus suis (S. suis) is a major swine pathogen and an emerging zoonotic agent. Serotypes 1, 2, 3, 7, 9, 14 and 1/2 are the most prevalent serotypes of this pathogen. However, almost all studies were carried out on serotype 2 strains. Therefore, characterization of genomic features of other serotypes will be required to better understand their virulence potential and phylogenetic relationships among different serotypes.ResultsFour Chinese S. suis strains belonging to serotypes 1, 7, 9 and 1/2 were sequenced using a rapid, high-throughput approach. Based on the 13 corresponding serotype strains, including 9 previously completed genomes of this bacterium, a full comparative genomic analysis was performed. The results provide evidence that (i) the pan-genome of this species is open and the size increases with addition of new sequenced genomes, (ii) strains of serotypes 1, 3, 7 and 9 are phylogenetically distinct from serotype 2 strains, but all serotype 2 strains, plus the serotype 1/2 and 14 strains, are very closely related. (iii) all these strains, except for the serotype 1 strain, could harbor a recombinant site for a pathogenic island (89 K) mediated by conjugal transfer, and may have the ability to gain the 89 K sequence.ConclusionsThere is significant genomic diversity among different strains in S. suis, and the gain and loss of large amount of genes are involved in shaping their genomes. This is indicated by (i) pairwise gene content comparisons between every pair of these strains, (ii) the open pan-genome of this species, (iii) the observed indels, invertions and rearrangements in the collinearity analysis. Phylogenetic relationships may be associated with serotype, as serotype 2 strains are closely related and distinct from other serotypes like 1, 3, 7 and 9, but more strains need to be sequenced to confirm this.
Highlights
Streptococcus suis (S. suis) is a major swine pathogen and an emerging zoonotic agent
Among the 33 serotypes that have been classified based on the composition of their capsular polysaccharides (CPS), only a limited number are responsible for infections in pigs, including serotypes 1-9 and 14 [24]
The distribution of different serotypes varies depending on the geographical origins of the strains, S. suis serotype 2 (SS2) is considered the most pathogenic and the most prevalent capsular type among diseased pigs, followed by serotypes 3 and 1/2 [25,26]
Summary
Streptococcus suis (S. suis) is a major swine pathogen and an emerging zoonotic agent. Serotypes 1, 2, 3, 7, 9, 14 and 1/2 are the most prevalent serotypes of this pathogen. Streptococcus suis (S. suis) is a major swine pathogen responsible for severe economic losses in the pork industry and is emerging as an important threat to human health, especially to people who have close contact with swine or pork by-products [1,2,3]. Among the 33 serotypes that have been classified based on the composition of their capsular polysaccharides (CPS), only a limited number are responsible for infections in pigs, including serotypes 1-9 and 14 [24]. The distribution of different serotypes varies depending on the geographical origins of the strains, S. suis serotype 2 (SS2) is considered the most pathogenic and the most prevalent capsular type among diseased pigs, followed by serotypes 3 and 1/2 [25,26]. Comparative genomic analysis is a powerful method for exploring the relationships between genotypes and phenotypes and for discovering genetic markers for clinical purposes
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