New structural insights into the PI-2 pilus from Streptococcus oralis, an early dental plaque colonizer

Dental plaque or oral biofilm is a major cause of periodontal disease, dental caries, and infections such as infective endocarditis. Attachment of pioneer bacteria (primary or early colonizers) to the tooth surfaces (e.g., the acquired salivary pellicle coated on the tooth surface) is the first and critical step in plaque development. Coaggregation between the primary colonizers promotes biofilm growth by providing attachment sites for the secondary or late colonizers to establish the environment for subsequent stages (i.e, microcolony formation, maturation, and dispersal). An opportunistic pathogen, Streptococcus oralis, is a primary colonizer of dental plaque, and its coaggregation with another primary colonizer, Actinomyces oris, helps to seed plaque development. Hair-like surface organelles called pili or fimbriae from these primary colonizers facilitate attachment and interbacterial interaction during biofilm formation. This study has used multiple approaches to obtain the three-dimensional structure of pilins or building blocks (PitA and PitB) of S. oralis PI-2 pili. The study also presents the first structural model for the S. oralis PI-2 pilus architecture, in which repeating PitB forms a backbone with the adhesive PitA positioned at the tip. For the first time, the study demonstrates that pilus-mediated bacteria-to-bacteria interactions during dental biofilm formation can occur via the tip adhesins. While these findings are preliminary and require further validation, they still provide a basis for exploring the anti-adhesive potential for targeting pilus-mediated interactions to control dental plaque biofilm growth and combat infections.

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New structural insights into the PI-2 pilus from Streptococcus oralis, an early dental plaque colonizer



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