Microalgae produce extracellular and intracellular metabolites with various biological activities, such as antibacterial and antiadhesive properties making them very interesting in various fields, including prevention of oral disease. The aim of the master thesis was to determine antibacterial and antiadhesive properties of Arthrospira platensis and Chlorella vulgaris microalgae extracts on Streptococcus cristatus and Staphylococcus warneri strains, isolated from oral cavity. Minimal inhibitory concentration (MIC) of MC, MS, CMAC and CMAS microalgae extracts (M: methanol extraction; CMA: extraction with mixture of chloroform, methanol and acetone; C: C. vulgaris; S: A. platensis) was determined by the microdilution method. To study bacterial adhesion, we use 0,1 MIC of microalgal extracts. The antiadhesive properties of the extracts were determined first on polysryrene surface by crystal violet staining method and then on dental surface by colony count method. The results showed that CMAS extract had the best antibacterial activity (MIC 10 mg/mL). At a subinhibitory concentration of 0.1 MIC, CMAS extract had antiadhesive activity against Strep. cristatus, as adhesion to polystyrene was reduced for 84 %, while adhesion of Staph. warneri was reduced for 36 %. On the dental surface, CMAS extract inhibited the adhesion of Staph. warneri, while it had no effect on adhesion of Strep. cristatus. The results of the experimental work confirm the complexity of studying the bioactive properties of natural extracts, which depends on many factors. The results show that the antibacterial and anti-adhesive activity of the microalgal extract depend on the extraction process, the type of solvent used, and the procedure used to test the bioactive properties (e.g. choice of the solvent in which the extracts are dissolved, choice of bacteria, choice of the surface, choice of the method) and type of microorganisms used. Obtained results show the antiadhesive properties of A. platensis and C. vulgaris microalgae extracts and suggest their possible application in field of oral hygiene
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