Researchers Identify Highly Antibiotic Resistant Bacteria at US Wastewater Treatment Plants


    Researchers Identify Highly Antibiotic Resistant Bacteria at US Wastewater Treatment Plants

    A team of researchers from the University of Maryland School of Public Health, in the United States, has found that the MRSA (methicillin-resistant Staphylococcus aureus) inhabits multiple WWTPs (Wastewater Treatment Plants) across the US territory. This specific type of Staphylococcus aureus is known to be the cause of many fatal bacterial infections. Before the year 2000, most of these fatal infections occured in hospitalized patients, however, after the year 2000 a rise in prevalence in healthy communities has been reported.

    According to the lead researcher of the study, assistant professor Amy Sapkota, the prevalence of these community-acquired MRSA infections is continuously rising. Despite this fact, researchers have not yet been able to identify the exact sources of MRSA infection. “This was the first study to investigate U.S. wastewater as a potential environmental reservoir of MRSA”, said Amy Sapkota.

    The current study has been published in the November issue of the journal Environmental Health Perspectives and is the first study to confirm the presence of MRSA in the wastewater treatment plants from the United States. A precedent study led by Swedish scientists  showed that MRSA was present in the wastewater treatment plants from Sweden.



    Researchers from the University of Nebraska Medical Center, in collaboration with the research team from the University of Maryland School of Public Health, collected water samples from four wastewater treatment plants (two from the Mid West and two from the Mid Atlantic area). The criteria through which these four wastewater plants were selected included the fact that discharged water is reused in irrigation. The aim of the study was to detect whether or not MRSA are still present in the discharged water.

    Along with the antibiotic resistant bacteria (MRSA), researchers found out that MSSA (methicillin-susceptible Staphylococcus aureus) was also present in the discharged water coming from all four wastewater treatment plants. The results show that 45% of the samples contained MRSA whilst 55% was MSSA. Before passing through the treatment plant, 83% of the water samples were shown to contain MRSA. However, after water was processed and treated, only samples from one wastewater treatment plant contained bacteria. These samples were taken from one of the plants that doesn’t regularly use chlorination in the treating process.

    From the isolated bacterial cultures, researchers found that 93% of the MRSA strains and 29% of the MSSA strains were resistant to more than two classes of antibiotics. According to the team of researchers, although water treatment plants are effective against reducing the number of bacteria through the treatment process, the same treatment plants might be responsible for increasing the number of extremely resistant bacteria. These are particularly the treatment plants that don’t use chlorination in the water treatment process.

    “Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater”, said doctoral student Rachel Rosenberg Goldstein, whilst concluding: “Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater”.

    Study Abstract

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