Antibiotic resistance represents a major public health challenge, while aquatic ecosystems can act as reservoirs of resistant bacteria and antimicrobial resistance genes (ARGs). In this master's thesis, we investigated the phenotypic and genotypic burden of antibiotic resistance in Lake Bled and its tributaries and evaluated the influence of spatial and seasonal factors on the distribution of resistant bacteria and ARGs. The susceptibility of 745 Escherichia coli isolates, obtained from water samples, to 16 antibiotics was analysed using the disk diffusion method. In addition, the presence of 69 target ARGs was determined by PCR in 140 metagenomic DNA samples. The phenotypic analysis showed a relatively low prevalence of resistance; 73,56 % of the isolates were susceptible to all tested antibiotics, whereas 14,6 % were multidrug-resistant (MDR). We also isolated 32 extended-spectrum betalactamase producing isolates, of which 87,50 % were MDR. The genotypic analysis revealed the presence of ARGs in all samples throughout the year, with the most frequently detected genes being blaTEM, blaOXA, tetA, tetC, sul2, dfrB, aadA, ermF, intI1, and genes encoding non-specific efflux pumps. The mcr-4 gene, associated with colistin resistance, was detected in more than one quarter of the samples. The highest ARG burden was detected in the tributaries outside the bathing season, whereas a slight increase in ARG burden was also observed in the lake during the bathing season. The results indicate that tributaries flowing through agricultural and urban areas are the main source of resistant bacteria and ARGs entering Lake Bled and that monitoring faecal indicator bacteria alone is insufficient for a comprehensive assessment of microbiological risk in recreational waters. The study highlights the importance of incorporating molecular analyses of antimicrobial resistance into future recreational water quality monitoring programmes.
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