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Abstract

Antimicrobial resistance is a global health issue. The discharge, maintenance and transfer of antimicrobial resistance to the aquatic environment and the risk this presents is relatively unknown. This work describes the presence and distribution of antimicrobial resistant Escherichia coli in surface waters of seven rivers in south east Queensland, Australia. Resistance to four antimicrobials (ampicillin, tetracycline, sulfamethoxazole and ciprofloxacin) was determined using a method combining chromogenic microbial detection with breakpoint antimicrobial resistance analysis. E. coli concentration and antimicrobial resistance was significantly higher (p < 0.05) at sites receiving WWTP discharge compared to sites with no direct WWTP discharge. There was a positive correlation (ρ < 0.001, r = 0.95) between E. coli concentration and volume of WWTP discharge into these rivers. This would suggest that WWTPs are the primary source of antimicrobial resistant E. coli in the study region. There was no correlation (ρ > 0.05) between WWTP discharge volume into rivers and incidence of antimicrobial resistance for ampicillin, sulfamethoxazole and tetracycline. However, there was a positive correlation (ρ < 0.01, r = 0.82) between incidence of ciprofloxacin resistance and WWTP discharge volume into rivers. This would suggest that E. coli resistance to ciprofloxacin found in the study area is driven primarily by WWTP discharge, with resistance to other investigated antimicrobials influenced by additional sources and/or drivers.