Occurrence of Antibiotic Resistant Fecal Indicator Bacteria in Point-Source Polluted Surface Waters

<div class="line" id="line-5"> Surface waters often receive wastewater treatment plant effluents (WWTP). These sources contribute to antibiotic levels and promote resistance in the water. The purpose of this study was to compare the occurrence of fecal indicator bacteria in beach water resistant to five commonly utilized antibiotics (tetracycline, ampicillin, sulfamethoxazole, ciprofloxacin, and vancomycin). Samples were collected five times in 2016 from a beach receiving UV disinfected WWTP effluents. Triplicates of diluted influent, secondary effluent, undiluted disinfected effluent and beach water were filtered (100 ml each) through a sterile membrane filtration system. Enterococci were enumerated by using Method 1600 and Escherichia coli by Method 1604. Antibiotic resistant fecal indicator bacteria (ARFIB) were enumerated by culturing a separate set of filters on mI Agar plates with tetracycline, ampicillin, sulfamethoxazole and ciprofloxacin at 37&mp; 0.5℃ and mEI Agar with vancomycin at 37&mp; 0.5℃ for 24 hrs. The resistance was calculated as percentages. E. coli resistant to sulfamethoxazole was the most commonly detected FIB (12%) at the beach and followed by ampicillin resistant E. coli (10%). Vancomycin-resistant Enterococci was the least detected FIB. The ARFIB concentrations significantly (p&lt;0.05) increased from influent to secondary effluent for ciprofloxacin and tetracycline in all five sampling events, indicating that E. coli gained resistance to these two antibiotics during treatment. This study presents that a WWTP with UV disinfection has been poorly removing ARFIB and contributing to their presence at the beach. A significant percentage (20%) of ampicillin resistant E. coli reached to the beach and exceeded the beach action value. Except for vancomycin, all beach water samples were positive for at least one type of ARFIB throughout the study. Recreational surface waters are at significant risk as antibiotic resistant bacteria may be introduced via point sources. Treatment efficiency of WWTP needs improvement to prevent antibiotic-resistant waterborne diseases among swimmers.</div>