The role of exopolysacacchirides and extracellular DNA in Streptococcus sanguinis escape from complement system

Author(s)

Victor Aragão Abreu de Freitas

• Document type: Doctoral Thesis
• Press: Piracicaba, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
• Defense date: 2023-03-17

Examining board members

Renata de Oliveira Mattos Graner; Marlise Inêz Klein; Antônio Pedro Ricomini Filho; Rodrigo Alex Arthur

• Advisor: Lívia Araujo Alves; Renata de Oliveira Mattos Graner

Abstract

Streptococcus sanguinis is an abundant commensal bacterial species of the oral cavity capable of initiating biofilms on tooth surfaces by evading salivary S-IgA1 antibodies through the expression of IgA1 protease, and by producing extracellular DNA (eDNA), as well as exopolysaccharides (EPS) from sucrose. This species is also commonly associated with opportunistic cardiovascular infections, which might imply the capacity to evade blood clearance immune functions mediated by the complement system. The aim of this study was to investigate the roles of eDNA, sucrose-derived EPS and IgA1 protease in the capacity of S. sanguinis to evade the complement system. To this end, deletion mutants of genes encoding for the IgA1 protease (iga), pyruvate oxidase required for the production of eDNA (spxB), and glucosyltransferase P (gtfP) required for the synthesis of EPS from sucrose were obtained in the S. sanguinis strain SK36 (respectively named SKiga, SKspxB and SKgtfP). Mutants were then compared with parent strain regarding their susceptibility to C3b deposition and to phagocytosis by neutrophils (PMN) isolated from human peripheral blood, in flow cytometry assays. Five wild-type strains from the oral cavity or from the bloodstream were also analyzed regarding their production of eDNA and/or EPS at different conditions, as well as to their profiles of C3b binding. The effects of bacterial treatment with DNAse I in C3b binding and opsonophagocytosis was also assessed in all the studied strains. Deletion of spxB and gtfP promoted significant increases in C3b deposition and opsophagocytosis by PMN under conditions which promote production of eDNA and sucrose-derived EPS, respectively (Kruskal Wallis with post hoc Dunn’s test; p<0.05). In addition, C3b deposition and/or opsonophagocytosis by PMN were significantly increased in wild-type strains with high production of eDNA after treatment with DNase I, as compared to the same strain not treated with DNAse I. Moreover, strains producing sucrose-derived EPS showed increased C3b deposition when grown in the absence of sucrose (to avoid EPS synthesis), when compared to the same strain grown in the presence of sucrose (p<0.05). No significant difference in C3b deposition or in opsophagocytosis were found in SKigA as compared to SK36. These findings indicate that the production of eDNA and sucrose-derived EPS contribute to S. sanguinis evasion to complement-mediated immunity, whereas expression of IgA proteases does not significantly affect the capacity of SK36 to evade the complement system (AU)

• FAPESP's process: 18/12248-0 - The role of exopolysaccharides and extracellular DNA in Streptococcus sanguinis evasion to complement system
• Grantee: Victor Aragão Abreu de Freitas
• Support Opportunities: Scholarships in Brazil - Doctorate