Although the recognized ecological niche of Escherichia coli is the gastrointestinal tract of humans and animals with a constant body temperature, recent studies have showed that some strains can survive and multiply in the environment. These so-called naturalized strains might carry genes for virulence factors and antimicrobial resistance, posing a risk to human and animal health. In this M. Sc. thesis, we determined the selected phenotypic and genotypic characteristics of 98 isolates of the genus Escherichia, which were isolated from water and sediment samples from the Divjak pond and water samples from the pond, which we designated as 2nd pond in Verd near Vrhnika. Seventy-three isolates were identified as E. coli and 25 as E. marmotae. The clonality of the isolates was determined using the ERIC-PCR method. The isolates were classified into phylogenetic groups according to the original (Clermont et al., 2000) and revised (Clermont et al., 2013) methods, with most isolates classified into phylogenetic group B1 according to the original (70.97 %) and revised (74.19 %) methods. The presence of a specific 476 bp amplicon, characteristic for the E. marmotae strains was confirmed in all E. marmotae isolates. We screened with molecular methods 18 virulence factor genes, eight β-lactamase genes, and three plasmid-mediated quinolone resistance genes. At least one virulence factor gene was confirmed in almost all isolates. We also tested haemolytic activity and phenotypic resistance to 10 selected antimicrobial agents. The latter was confirmed in 5 E. coli isolates and 1 E. marmotae isolate. Plasmid DNA from selected isolates was sent for sequencing to Microsynth, Switzerland. Analysis revealed the presence of small plasmids with different origins of replication and expected regulation of replication by antisense RNA.
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