From orthodontic separators to the heart
: A laboratory-based study of oral streptococcal blood survival mechanisms

Student thesis: Doctoral ThesisDoctor of Dental Surgery (DDS)


The association between dental procedures, oral bacteria and infective endocarditis (IE)
is contentious, particularly following changes in UK guidance on antibiotic prophylaxis in
recent years. Although IE in children is rare, the disease carries a high risk of mortality
and morbidity, and several cases of orthodontic-induced IE have been reported.
Evidence suggests that orthodontic separator placement induces bacteraemia with oral
streptococci, potential causative agents in IE. However, a detailed understanding of how
such bacteria survive in blood is currently lacking.
This study aimed to determine the blood survival mechanisms of oral streptococci
commonly implicated in orthodontic separator placement. In particular, the role of
bacterial surface determinants and evasion of complement-mediated killing in
promoting streptococcal survival in blood were investigated.
This work identified that bacterial blood survival rates are species- and straindependent, with a general correlation between IE-associated species and persistence
in blood. IE pathogen Streptococcus gordonii surface proteins PadA and Hsa both
bound Factor H and vitronectin, indicating two mechanisms by which S. gordonii may
evade the host immune system.
Better understanding of mechanisms for streptococcal survival in the bloodstream,
such as those identified in this project, could identify novel targets for the prevention
or treatment of IE in the future.
Date of Award26 Nov 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAngela H Nobbs (Supervisor) & Tony Ireland (Supervisor)

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