The purpose of the master's thesis was testing the resistance of bacteria Bacillus subtilis in biofilm against antimicrobial agents and mechanical stress with the main focus on finding out the importance of protein TasA and exopolysaccharides EpsA-O. In the first part, using a modular oscillatory rheometer, we determined the basic rheological properties of biofilms of various mutants, such as elastic and viscous modulus, cohesive energy, and damping factor. To test the resistance against antimicrobial agents, we added propidium iodide as a viability stain and then we treated wild type and mutant strains deficient in exopolymer production with antibiotics daptomycin, erythromicin or vankomycin. The antibiotics’ efficiency was then evaluated by spectrofluorometry. Very similarly, we tested the resistance against mechanical stress by the use of ultrasound disintegrator. The results obtained during the experiments indicate that the retention of water in the biofilm and its protection against antimicrobial agents, such as the antibiotic daptomycin, can be attributed to the important role of the TasA protein and exopolysaccharides. The latter are also important for maintaining the consistency of the biofilm and protecting cells within it. Equally important is the finding that antibiotics targeting cellular metabolism were entirely ineffective against mature biofilm.
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