Microbial resistance to antibiotics and biofilm formation represent a major problem in the food chain and medicine. In order to establish control strategies and manage infections associated with antimicrobial resistance and biofilm formation, it is important to understand the potential target mechanisms at the phenotypic and genotypic level. In the master's thesis, we characterized the resistance and biofilm formation of Gram positive bacteria and Gram-negative bacteria phenotypically and genotypically. At the phenotypic level, we determined the minimum inhibitory concentration values for the antibiotics erythromycin, vancomycin, kanamycin, ciprofloxacin, ampicillin and tetracycline using microdilution method and resazurin staining. Biofilm formation was evaluated by staining the biofilm biomass with crystal violet dye. To determine resistance to antibiotics and biofilm formation at the genotypic level, we obtained the whole genome sequences of the selected bacteria and analysed them using bioinformatics tools. Phenotypic characterization of microbial resistance to antibiotics showed heterogeneous resistance of the selected bacteria. Based on the phenotypic characterization of biofilm formation, we determined L. monocytogenes ATCC 19115 and S. aureus ATCC 25923 as the most biofilm-forming bacteria. We selected S. aureus ATCC 25923 as a model organism and determined 69 compounds with anti-biofilm activity among 862 active compounds of the Faculty of Pharmacy library. We highlighted compounds 6C3, 6B3 and 6B4, which mimic D-alanine, and compounds 10C8 and 10D8, which belong to the cyanothiophene inhibitors of the MurF enzyme. Genotypic characterization, based on the aph(3′)-IIb and blaCMH-3 genes, allowed the identification of two molecular mechanisms of antibiotic resistance, the enzyme aminoglycoside phosphotransferase, a mechanism of resistance to kanamycin, and the enzyme β-lactamase, a mechanism of resistance to ampicillin.
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