Author:

Abstract:

Periodontal diseases are a significant public health burden, of which severe periodontitis is the 6th-most prevalent disease, affecting 11% of the global population. Periodontitis is defined as infections of the tooth supporting tissue, leading to destruction of the connective tissue and alveolar bone, eventually resulting in tooth loss. While dental biofilm are known to play a major role in the development of periodontal diseases, the exact microbial etiology is still unknown. The ecological plaque hypothesis states that the host, the environment, the presence of periodontal pathogens and the absence of beneficial bacteria are the most important factors in the development of periodontal diseases. The shift from a homeostatic microbial composition towards a dysbiotic microbiota in a susceptible host will lead to the development of periodontitis. To date, standard periodontal therapy focuses mainly on the reduction and elimination of the bacterial load with subsequent improvement in clinical parameters. However, fast bacterial translocation and recolonization increases the risk of recurrence of disease, making maintenance therapy a lifelong requirement for the patients. One new treatment strategy focuses on controlling recolonization by means of probiotic bacteria. Although the use of certain probiotic bacteria resulted in an improvement in clinical parameters as well as in a delayed recolonization by pathogenic bacteria, the colonization of probiotic bacteria in the oral cavity is only temporary. Therefore, the stimulation of the protective and beneficial properties of the natural resident microbiota might reveal a new treatment approach. The prebiotic concept has already been introduced in gastrointestinal health. By means of specific food ingredients, selective changes in the composition or activity of the indigenous gastrointestinal are induced, thus conferring health benefits to the host. The main aim of this thesis was to investigate if the prebiotic concept can be transferred to oral health to reveal an alternative treatment approach for periodontitis. To identify potential prebiotic compounds for oral health, Phenotype MicroArrays were used as a high-throughput method to monitor the change in respiratory activity of 16 oral bacteria in response to 759 nutritional compounds. Multivariate statistical analysis was employed to investigate metabolic associations within and among bacterial groups, analyzing collaborative or competitive interactions of bacteria. Further, compounds were selected based on their selective stimulation of individual bacteria in metabolic activity, growth and biofilm formation. Seven compounds were subsequently used in dual species competition assays of beneficial and pathogenic bacteria. N-acetyl-D-mannosamine, L-arginine, and beta-methyl-D-galactoside selectively stimulated beneficial oral bacteria, leading to a suppression of pathogenic species. Hence, mixed species biofilm communities were shifted towards a composition dominated by beneficial oral bacteria at in vitro level. To validate the selective stimulatory effect of beneficial bacteria, a chemostat culture containing 14 model bacteria was developed. Nine potential prebiotic substrates were tested on these multispecies biofilms, and biofilm composition was analyzed by vitality qPCR. N-acetyl-D-mannosamine, succinic acid, and the di-peptide Met-Pro were able to stimulate the beneficial proportion of the biofilm to above 95%. Additionally, the effect of environmental factors, such as pH, nutrient availability, oxygen concentration and prebiotic dose, on the efficacy of the prebiotic substances was evaluated. Throughout the experiments, N-acetyl-D-mannosamine could be identified as the most promising prebiotic compound, shifting the biofilm composition despite changing conditions towards a beneficial dominated community of 97%. In addition, the potential of N-acetyl-D-mannosamine to increase the resistance of established beneficial biofilms to invading pathogens was analyzed. Incorporation of pathogenic species was significantly decreased when compared to the control treatment, thus, possibly enabling the use of prebiotics to control or prevent the translocation and recolonization of pathogenic bacteria in the oral cavity. Although the exact mechanism of the prebiotic treatment needs to be investigated, data indicated that N-acetyl-D-mannosamine also interferes with the co-aggregation of beneficial and pathogenic bacteria. The prebiotic concept shows promising potential as a new treatment approach for periodontal diseases by shifting the bacterial composition of mixed biofilm communities towards a health associated microbiota and preventing the incorporation of pathogenic bacteria into established biofilms.