Slovenia is one of the most water-rich countries in Europe, where water is important not only for drinking, but also for swimming. Several Slovenian rivers, lakes and the sea meet the criteria for natural bathing waters where water quality is monitored during the bathing season and many of them are marked with a blue flag, while in some bathing resorts, (mainly visited by locals), the water is not monitored. Bathing water quality criteria are based on the number of fecal indicators i.e. Escherichia coli and intestinal enterococci. Due to a plastic genome, E. coli strains are very diverse and range from non-pathogenic to pathogenic, where both may carry antimicrobial resistance genes (ARGs).
To evaluate the antimicrobial resistance and pathogenic potential of E. coli for bathers, after isolation and ERIC-PCR analysis nonclonal isolates of E. coli from controlled (Lake Bled and sea at the central beach of Portorož) and uncontrolled natural bathing waters (river bathing area downstream of a wastewater treatment plant (WWTP) (Savinja River) were examined for the presence of virulence associated genes (VAGs) and ARGs. Phenotypic resistance to antimicrobials was also tested.
Preliminary results show high clonal diversity in lake water, followed by river and sea water. The isolates were assigned to all phylogenetic groups, with 20% of isolates, mainly from Lake Bled and Savinja River, belonging to group B2. The higher number of B2 isolates in Lake Bled, correlates with the time period of use of fertilizer in agriculture in the immediate vicinity of lake. The percentage of VAGs detected in isolates from Lake Bled ranged from 3 to 22%. The presence of specific ARGs (CTX-M, SHV/TEM, PMQR) was confirmed in all sampled waters, with the genes of groups CTX-M1 and qnrB dominating in isolates from the Savinja River and CTX-M 1, 2, 8 and 9 group genes from Lake Bled.
The results of our study show that the number of E. coli indicates only the level of contamination with faecal bacteria and does not reflect the real disease-causing potential for humans and the spread of antimicrobial resistant bacteria and ARGs in and between humans and the environment.