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Infect Immun. 2019 Jul 15. pii: IAI.00406-19. doi: 10.1128/IAI.00406-19. [Epub ahead of print]

Streptococcus oralis subsp. dentisani produces mono-lateral serine rich repeat protein fibrils one of which contributes to saliva binding via sialic acid.

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Center for Microbial Pathogenesis, Abigail Wexner Research Institute at Nationwide Children's Hospital, Columbus, OH, USA.
Medical Student Research Program, The Ohio State University College of Medicine, The Ohio State University, Columbus, Ohio, USA.
Institute for Genomic Medicine, Abigail Wexner Research Institute Nationwide Children's Hospital, Columbus, OH, USA.
Diamond Light Source, Harwell Science & Innovation Campus, Didcot, Oxfordshire UK.
Department of Pediatrics, The Ohio State University, Columbus, Ohio, USA.
Institute of Medical Microbiology, German National Reference Center for Streptococci, University Hospital (RWTH), Aachen, Germany.
Center for Microbial Pathogenesis, Abigail Wexner Research Institute at Nationwide Children's Hospital, Columbus, OH, USA.


Our studies reveal the oral colonizer and cause of infective endocarditis Streptococcus oralis subsp. dentisani displays a striking mono-lateral distribution of surface fibrils. Furthermore, our data suggest that these fibrils impact the structure of adherent bacterial chains. Mutagenesis studies indicate that these fibrils are dependent on three serine rich repeat proteins (SRRPs) here named Fibril Associated Proteins (Fap) A, B and C and that each SRRP forms a different fibril with a distinct distribution. SRRPs are a family of bacterial adhesins that have diverse roles in adhesion and can bind to different receptors through modular non-repeat region domains. Amino acid sequence and predicted structural similarity searches using the non-repeat regions suggested that FapA may contribute to interspecies interactions, FapA and B to intraspecies interactions and FapC to sialic acid binding. We demonstrated that a fapC mutant was significantly reduced in binding to saliva. We confirmed a role for FapC in sialic acid binding by demonstrating that the parental strain was significantly reduced in adhesion upon addition of a recombinantly-expressed, sialic acid-specific, carbohydrate binding module while the fapC mutant was not reduced. However, mutation of a residue previously shown to be essential for sialic acid binding did not decrease bacterial adhesion, leaving the precise mechanism of FapC mediated adhesion to sialic acid to be defined. We also demonstrated that presence of any one of the SRRPs is sufficient for efficient biofilm formation. Similar structures were observed on all infective endocarditis isolates examined, suggesting this distribution is a conserved feature of this S. oralis subspecies.


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