Abstract
Streptococcus suis serotype 2 is an important porcine bacterial pathogen and zoonotic agent responsible for sudden death, septic shock, and meningitis. However, serotype 2 strains are heterogeneous, composed of a multitude of sequence types (STs) whose distribution greatly varies worldwide. Of the virulence factors presently described for S. suis, the capsular polysaccharide (CPS) is a critical factor implicated in a multitude of functions, including in impairment of phagocytosis and innate immune cell activation by masking underlying bacterial components. However, these roles have been described using Eurasian ST1 and ST7 strains, which greatly differ from North American ST25 strains. Consequently, the capacity of the CPS to mask surface antigens and putative virulence factors in non-Eurasian strains remains unknown. Herein, the role of the S. suis serotype 2 CPS of a prototype intermediate virulent North American ST25 strain, in comparison with that of a virulent European ST1 strain, with regards to interactions with dendritic cells, as well as virulence during the systemic phase of infection, was evaluated. Results demonstrated that the CPS remains critical for virulence and development of clinical disease regardless of strain background, due to its requirement for survival in blood. However, its role in the interactions with dendritic cells is strain-dependent. Consequently, certain key characteristics associated with the CPS are not necessarily applicable to all S. suis serotype 2 strains. This indicates that though certain factors may be important for S. suis serotype 2 virulence, strain background could be as determining, reiterating the need in using strains from varying backgrounds in order to better characterize the S. suis pathogenesis.
Highlights
Deletion of cpsF or neuC genes involved in S. suis serotype 2 capsular polysaccharide biosynthesis results in non-encapsulation of a ST25 strain
Deletion of cpsF or neuC gene significantly increased surface hydrophobicity of all mutants (p < 0.001), which averaged 95% (Fig 1). These results confirm that deletion of S. suis serotype 2 capsular polysaccharide (CPS) biosynthesis genes results in high surface hydrophobicity, regardless of strain background
Biosynthesis of the S. suis serotype 2 CPS involves a variety of genes encoded by the cps locus of which mutants deficient for cpsB, cpsE, cpsF, cpsG, cpsJ, cpsL, neuB, and neuC have been created, all using Eurasian strain P1/7 (ST1) strains or the Chinese ST7 strain [16, 18, 19, 34, 40]
Summary
The objective of this study was to evaluate the role of the S. suis serotype 2 CPS of a prototype intermediate virulent North American ST25 strain, in comparison with that of a virulent European ST1 strain, with regards to interactions with DCs, as well as virulence during the systemic phase of infection
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