Breaking barriers How Porphyromonas gingivalis travels through the oral mucosa using Candida albicans

Increasing evidence shows that periodontitis is associatedwith various diseases such as Alzheimer's disease. Porphyromonas gingivalis isa keystone pathogen of periodontitis and has been found in affected organs. Howthis bacterium travels from the oral cavity to these organs is unknown. The aimof this thesis was to study how P. gingivalis can pass the oral mucosa,which would be the first barrier. Four possible mechanisms are described. Thelatter two mechanisms involving the fungus Candida albicans and hostmacrophages were investigated in this thesis. It was found that P.gingivalis survives in oxygen-rich conditions when C. albicans ispresent, where it cannot survive alone. In addition, P. gingivalis canphysically adhere to the hyphae of C. albicans. Macrophages areattracted by C. albicans and can take up P. gingivalis from thehyphae of C. albicans. However, it could not be determined whether P.gingivalis survives within macrophages. The method used to quantifyintracellular bacteria was altered for P. gingivalis, but it wasconfirmed that this redesign is flawed. Lastly, P. gingivalis cansurvive in a model of the oral mucosa without C. albicans, and it penetratesinto the tissue undetected. C. albicans enhances this penetration andtriggers the immune response. Overall, the findings of this thesis provideevidence on how P. gingivalis can travel through the oral mucosa. Targetingthe adherence of P. gingivalis to C. albicans or reducing theattraction of macrophages to C. albicans could provide new treatmentoptions to reduce the development of various diseases.