The oral cavity represents a habitat for many species of microorganisms, which in certain conditions can cause various diseases, such as periodontal disease. Since current treatment guidelines do not lead to desired results, new approaches are under development, which also includes local treatment with probiotics. This approach is based on the inhibition of the growth of periodontal pathogenic bacteria, and due to the growth of probiotic bacteria and the formation of a probiotic biofilm prevents re-colonization of pathogenic microbes. The purpose of the master's thesis was to obtain autohtonous bacterial strains with antimicrobial effect against periodontal pathogenic bacteria Aggregatibacter actinomycetemcomitans from the oral cavity of individuals with small number of dental fillings. In order to obtain bacterial strains with antimicrobial effect, we have developed a protocol of sampling the oral cavity. We evaluated the effect of food intake on the appearance of strains with antimicrobial effects, so we performed the sampling at different time points (morning, afternoon, and a so-called sampling with minimal impact of food). We also checked whether the strains with antimicrobial activity are present in all ecological biotopes, therefore samples were taken from four different positions in the mouth (saliva, buccal mucosa, tongue and the surface of the tooth). We used the enrichment medium for the isolation of actinomycetes and Gram-positive bacteria. In the next step, we have developed a method for the evaluation of the antimicrobial effect of the isolated bacteria on the bacteria Escherichia coli and Aggregatibacter actinomycetemcomitans. We have found that isolated bacterial strains from the oral cavity show an antimicrobial effect on A. actinomycetemcomitans from all sites of the oral cavity and from all time points. Thus, we have shown that the hypothesis of ecological niche, and the hypothesis of emigration and immigration contribute to a healthy oral flora. In the final phase of the research, we characterized isolated bacteria with antimicrobial effect by molecular microbiological methods. Most strains isolated from the oral cavity with antimicrobial effect against A. actinomycetemcomitans belong to the genus Bacillus. Based on the obtained results we may suggest the genus Bacillus as a probiotic method for treatment of periodontal disease. Our study is the first case in which we have isolated bacteria from the oral cavity belonging to the genus Bacillus, with antimicrobial effect on periodontal pathogenic bacteria A. actinomycetemcomitans.
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