We analysed 125 Escherichia coli isolates from swabs taken from footpaths in tourist caves in Slovenia and from bat guano sampled by the Karst Research Institute ZRC SAZU. E. coli is an important intestinal bacterium in humans and endothermic animals and is generally considered an indicator of faecal pollution. Although most E. coli strains are commensals, they can also become pathogens if they acquire virulence factor genes. Such strains can also be frequently resistant to antimicrobial agents, posing a major threat to humans worldwide. The objective of the thesis was to characterise E. coli isolates and determine their pathogenic potential and resistance to antimicrobial agents. Isolates were classified into 75 different clonal groups using the ERIC-PCR method. Non-clonal strains were assigned to phylogenetic groups according to the original and revised protocol. Molecular methods were used to examine all strains for the presence of 37 virulence genes, genes encoding beta-lactamases, and sequence types. It was also determined whether the strains exhibited hemolysis and resistance to antimicrobial agents. The majority of strains from surface swabs were assigned to phylogroup B1 (43 %) and strains from guano were mainly assigned to phylogroup B2 (36 %). The strains isolated from bat guano had an average of 7 virulence factor genes per strain, while the strains from surface swabs had 5 genes. The most virulent strain from guano had 19 genes, while the most virulent strain from surface swab had 21 genes. Interestingly, only 7 strains (15 %) from surface swabs and 2 strains (7 %) from guano were resistant to at least one of the antimicrobials tested.
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