Prevalence of β-Lactam and Sulfonamide Resistance Genes in a Freshwater Reservoir, Lake Bret, Switzerland

The spread of antibiotic resistance bacteria and their resistance genes (ARGs) represents a great concern to public health worldwide. The aquatic ecosystems are considered as hot spot for horizontal gene transfer, and sediments act as a reservoir of different contaminants. However, the occurrence of agricultural versus medical ARGs in Swiss freshwater reservoirs is understudied. Consequently, in this study, we aimed to quantitate broad-spectrum beta-lactam and sulfonamide resistance genes (bla(TEM), bla(SHV), bla(CTX-M), bla(NDM), sul1, and sul2) and the total bacterial load (16S rRNA genes) from the total DNA extracted from the surface sediments of the Lake Bret, Switzerland using quantitative polymerase chain reaction. In addition, sediment physicochemical parameters including organic matter, grain size, and toxic metal were analyzed. The results highlight the widespread dissemination of bla(TEM), bla(SHV), and sul1, which were also highly correlated to bacterial biomass and organic matter content (R > 0.75, p < 0.05). The bla(CTX-M) and sul2 were occasionally present and positively correlate with the concentrations of Cr, Mn, Fe, and Ni, linking it to agricultural practices. These findings demonstrate a fixation of last ARGs' generation in the environment, whereas actual antibiotic regulation tends to limit the dissemination of other ARGs in the studied lake reservoir.