EFFECTS OF ANTIBIOTICS AND MULTIDRUG RESISTANT E. COLI ON BACTERIAL SEDIMENT COMMUNITIES

Abstract

The spread of antibiotic resistance is a global health concern, with growing evidence that environmental reservoirs such as aquatic sediments play a role in antibiotic resistance persistence and dissemination. This study investigates the effects of a mixture of antibiotics and the establishment of a multidrug-resistant strain of Escherichia coli at levels commonly discharged by wastewater treatments plants on freshwater sediment bacterial communities. In addition, the study evaluates how the potential E. coli establishment was affected by the occurrence of antibiotics. To assess the effect and interaction of these two variables, a 10-day static test was performed in microcosm conditions using sediment from Lake Vänern, Sweden. Prior to the full experiment, a pilot study was performed to assess the invasion capacity of E. coli on sediment and how to prepare the inoculation of E.coli in the sediment. Results from the pilot study demonstrated that E.coli was able to survive and establish in the sediment for up to 28 days. In the full experiment an increase of the blaCTX-M gene in the sediment invaded by E.coli was observed after 1, 3, and 7 days after inoculation, indicating potential resistance spread to natural bacterial communities. The occurrence of antibiotic contamination positively affected the spread of antibiotic resistance genes (ARGs) on natural communities. The functions of the community were resilient to both the exposed antibiotic mixture and the invasion of the E.coli, attributed to functional redundancy in the bacteria communities and no-ecological effects of acquiring ARGs. The bacterial communities appear to have a higher carbon metabolism and a higher nitrification over time, attributed to an increasement on their efficiencies in using carbon and ammonium. These findings underscore the potential of invading bacteria carrying ARGs, such as E.coli, to influence the resistome of bacterial communities, and how this is modulated by the occurrence of antibiotic contamination. This study highlights the importance of incorporating environmental dimensions into antibiotic resistance research and supports a One Health approach to managing antimicrobial resistance.