PepO and CppA modulate Streptococcus sanguinis susceptibility to complement immunity and virulence.

Area of Science:

• Microbiology
• Immunology
• Pathogenesis

Background:

• Streptococcus sanguinis is a common oral bacterium that can cause cardiovascular infections.
• Understanding the virulence factors of S. sanguinis is critical for combating opportunistic infections.

Purpose of the Study:

• To investigate the roles of endopeptidase O (PepO) and C3-degrading protease (CppA) in the systemic virulence of S. sanguinis.
• To determine how PepO and CppA contribute to complement evasion and host interactions.

Main Methods:

• Generation of isogenic pepO and cppA mutants in S. sanguinis strain SK36.
• Assessment of susceptibility to complement C3b deposition and opsonophagocytosis by human neutrophils.
• Analysis of binding to complement regulators (SAP, C1q, C4BP, FH).
• Evaluation of ex vivo persistence in human blood and serum-mediated endothelial cell invasion.
• Virulence testing in a Galleria mellonella infection model.
• RT-qPCR analysis of pepO and cppA transcriptional activity across multiple strains.
• Phylogenetic analysis of PepO and CppA homologues.

Main Results:

• PepO and CppA mutants exhibited increased susceptibility to C3b deposition and neutrophil opsonophagocytosis.
• Mutants showed altered binding to complement components and reduced interaction with complement regulators C4BP and FH.
• Defects in ex vivo persistence, serum-mediated endothelial cell invasion, and Galleria mellonella virulence were observed in the mutants.
• PepO and CppA expression profiles were strain-specific, with variations in amino acid sequences, particularly in CppA.
• Phylogenetic analysis indicated independent evolutionary origins for PepO and CppA in S. sanguinis.

Conclusions:

• PepO and CppA are essential complement evasion proteins contributing to S. sanguinis virulence.
• Their expression is regulated in a strain-specific manner, influencing interactions with the host immune system.
• These proteins play multifaceted roles in bacterial survival, immune evasion, and pathogenesis, particularly in cardiovascular infections.