From Wastewater to Your Tap Water: The Vicious Cycle of Antibiotic Resistance

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1 Victoria Sullivan BioTAP March 23, 2015 From Wastewater to Your Tap Water: The Vicious Cycle of Antibiotic Resistance Multi-drug resistant pathogens pose a great challenge to the treatment of infectious diseases. This challenge is being propagated by the common use of broad spectrum antibiotics and has been listed by the World Health Organization as one of the three largest threats to public health in the 21st century (Rodriguez-Mozaz et al., 2015). A recent study by Rodriguez-Mozaz et al. gives insight as to why antibiotic resistance is such a challenge and how we are making it worse in a vicious cycle. This study provides evidence that human-mediated activities are increasing the presence of multi-drug resistant bacteria, particularly due to the selective pressures caused by the antibiotic pollution of a local hospital. This research aims to provide evidence that increased antibiotics and increased antibiotic resistance genes are directly leading to an increased level of multi-drug resistant pathogens in the environment. This particular hospital s pollution of antibiotics and antibiotic resistance genes as well as the wastewater treatment plant s inability to properly eradicate them help select for antibiotic resistant bacteria in the surrounding aquatic ecosystem (Rodriguez-Mozaz et al., 2015). The pollution caused by these institutions tend to have high levels of antibiotic resistance genes due to the common and liberal use of antibiotics in hospitals. Also, the river that the pollution from the hospital is affecting is a major source of drinking water and therefore helps the study

2 show how antibiotic resistance is impacting local communities. This experiment has far reaching implications and highlights the hazardous habits of careless antibiotic use. Rodriguez-Mozaz et al. performed the study by sampling the concentrations of various antibiotics and corresponding antibiotic resistance genes along the Ter River in Girona, Spain. The five sampling points included the wastewater effluents from the Girona hospital, influents and effluents from the Girona wastewater treatment plant, and an upstream and downstream location from the wastewater treatment plant on the Ter River (Rodriguez-Mozaz et al., 2015). The location of the sampling is arguably the most important aspect of the study because it traces the fluctuations in concentrations of antibiotics and antibiotic resistance genes and provides implications for how antimicrobial resistance is being spread throughout an aquatic ecosystem. The relationship between antibiotic resistance genes and the presence of antibiotics was investigated in this study. The antibiotics chosen for this study varied in families and included: β- lactams, lincosamides, macrolides, quinolones/fluoroquinolones, sulfonamides, tetracyclines, dihydrofolate reductase inhibitors and nitroimidazoles (Rodriguez-Mozaz et al., 2015). Five antibiotic resistance genes were selected based on clinical importance including blatem (resistance to β-lactams), qnrs (reduced susceptibility to fluoroquinolones), ermb (resistance to macrolides), suli (resistance to sulfonamides) and tetw (resistance to tetracyclines) genes (Rodriguez-Mozaz et al., 2015). The efficacy of the receiving wastewater treatment plant was observed by noting the incomplete removal of antibiotics and antibiotic resistance genes from upstream and downstream samples of the river. The actual sampling was done through sterile filtration of water samples over three trials. Other similar studies have analyzed the emergence of these pollutants, but none have investigated a hospital, its urban wastewater system, and the

3 affected river. This study shows the direct impact of the hospital on the surrounding aquatic environment and therefore is an excellent way to see the impacts of human-mediated activities on the spread of multi-drug resistant pathogens. The data collected show the significant presence of antibiotics/antibiotic resistance genes in the aquatic ecosystem surrounding the local hospital. The actual data collected were concentrations of antibiotics and antibiotic resistance genes found in various water samples. They analyzed these data using qpcr assays to determine which antibiotics or antibiotic resistant genes were present in the samples and statistical analyses to compare significant differences in concentrations (Rodriguez-Mozaz et al., 2015). One pattern noted in the results was that increased medical consumption of particular antibiotics unsurprisingly led to increased concentrations in hospital effluent samples. For example, antibiotics in the flouroquinolones family were detected at the highest concentrations likely due to their widespread use in hospitals. Sulfamethoxazole and trimethoprim were also found in high concentrations, and had similar readings due to their combined therapeutic use. This is an important pattern to note because approximately 80% of the antibiotics initially detected were also found in the samples of the river water, suggesting their widespread presence in the aquatic ecosystem as well as the wastewater treatment plant s inability to adequately filter them out (Rodriguez-Mozaz et al., 2015). Although the wastewater treatment plant was efficient at removing certain antibiotics, potentially hazardous amounts of other antibiotics were still found in the effluents that may be enough to affect microbial communities and select for resistance. Some actually showed significantly higher concentrations in post-wastewater treatment plant waters than before it. This suggests that the effluents of wastewater treatment plants could actually contribute to the spread

4 of antibiotic resistance genes, and therefore that the wastewater treatment plant may become a key place for horizontal gene transfer. An example of how this may work is shown in the concentration of the antibiotic resistance gene qnrs. With higher fluoroquinolone concentrations, selective advantage is given to resistant bacteria that can acquire this gnrs gene in order to survive the presence of the antibiotic (Rodriguez-Mozaz et al., 2015). To determine potential links between the concentration of antibiotics and their corresponding antibiotic resistance genes, the study carried out a correlation analysis. They concluded that there were indeed significant positive correlations between the concentrations of antibiotics and their antibiotic resistance genes. These data show that the resistance genes increase proportionally to the concentrations of the antibiotics due to selective pressures. They determined that further studies need to be done to further show these relationships and prove that wastewater treatment plants promote horizontal gene transfer among aquatic bacterial populations. The study concluded that the high concentrations of antibiotics and antibiotic resistance genes are indeed impacting the receiving river water. The wastewater treatment plant is contributing to the spread of antibiotic resistance and the levels of these antibiotics and antibiotic resistance genes are enough to affect microbial communities. The Ter River is a major source of drinking water for the city of Girona as well as the surrounding communities of Barcelona. Consequently, the antibiotic resistance that has been selected for in this water source will have a direct impact on these communities and likely pose a threat due to the multi-drug resistant pathogens that could now be in the aquatic ecosystem. While this study has conclusive, far reaching evidence on the negative impact of antibiotic/antibiotic resistance gene pollution, they

5 do assert the value of further research on the topic in order to better our understanding of they spread of antibiotic resistance. The vicious cycle of antibiotic resistance is clearly delineated in this study, and it highlights the serious threat of the issue in today s society. A short term solution would be to increase the efficiency of the wastewater treatment plant and thereby stop the antibiotic pollution from institutions such as hospitals. However, a long term plan, which is in more dire need, involves stopping the common use of broad spectrum antibiotics and funding research for more specific antibiotics. Without this desperately needed change, the vicious cycle of antibiotic resistance will continue to spiral our of our control. We are continuously making it harder for ourselves to treat our own problems, and this cycle needs to come to an abrupt stop. Citation: Rodriguez-Mozaz S, Chamorro S, Marti E, Huerta B, Gros M, Sánchez-Melsió A, Borrego CM, Barceló D Balcázar JL. Occurrence of antibiotics and antibiotic resistance genes in hospital and urban wastewaters and their impact on the receiving river. Elsevier Ltd Feb 1; 69: