'Superbug' MRSA identified in U.S. wastewater treatment plants

Sponsored by

College Park, MD, Nov. 5, 2012 -- A team led by researchers at the University of Maryland School of Public Health has found that the superbug methicillin-resistant Staphylococcus aureus (MRSA) is prevalent at several U.S. wastewater treatment plants. MRSA is well known for causing difficult-to-treat and potentially fatal bacterial infections in hospital patients, but since the late 1990s it has also been infecting otherwise healthy people in community settings.

"MRSA infections acquired outside of hospital settings -- known as community-acquired MRSA or CA-MRSA -- are on the rise and can be just as severe as hospital-acquired MRSA. However, we still do not fully understand the potential environmental sources of MRSA or how people in the community come in contact with this microorganism," says Amy R. Sapkota, assistant professor in the Maryland Institute for Applied Environmental Health and research study leader. "This was the first study to investigate U.S. wastewater as a potential environmental reservoir of MRSA."

Because infected people can shed MRSA from their noses and skin and through their feces, wastewater treatment plants are a likely reservoir for the bacteria. Swedish researchers have previously identified the presence of MRSA in wastewater treatment plants in Sweden, and this new UMD-led study confirms the presence of MRSA in U.S. facilities. The study was published in the November issue of the Environmental Health Perspectives journal.

The research team, including University of Maryland School of Public Health and University of Nebraska Medical Center researchers, collected wastewater samples throughout the treatment process at two Mid-Atlantic and two Midwestern wastewater treatment plants. These plants were chosen, in part, because treated effluent discharged from these plants is reused as "reclaimed wastewater" in spray irrigation activities. The researchers were interested in whether MRSA remained in the effluent.

They found that MRSA, as well as a related pathogen, methicillin-susceptible Staphylococcus aureus (MSSA), were present at all four wastewater treatment plants, with MRSA in half of all samples and MSSA in 55 percent. MRSA was present in 83 percent of the influent -- the raw sewage -- at all plants, but the percentage of MRSA and MSSA-positive samples decreased as treatment progressed. Only one wastewater treatment plant had the bacteria in the treated water leaving the plant, and this was at a plant that does not regularly use chlorination, a tertiary step in wastewater treatment.

Ninety-three percent of the MRSA strains that were isolated from the wastewater and 29 percent of MSSA strains were resistant to two or more classes of antibiotics, including several that the U.S. Food and Drug Administration has specifically approved for treating MRSA infections. At two wastewater treatment plants, MRSA strains showed resistance to more antibiotics and greater prevalence of a gene associated with virulence at subsequent treatment stages, until tertiary chlorination treatment appeared to eliminate all MRSA. This suggests that while wastewater treatment plants effectively reduce MRSA and MSSA from influent to effluent, they may select for increased antibiotic resistance and virulence, particularly at those facilities that do not employ tertiary treatment (via chlorination).

"Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater," says Rachel Rosenberg Goldstein, environmental health doctoral student in the School of Public Health and the study's first author. "Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater."

###

Sponsored by

TODAY'S HEADLINES

EPA awards over $17M in Great Lakes Restoration Initiative grants to address algal blooms

The Environmental Protection Agency has announced the award of 14 Great Lakes Restoration Initiative grants totaling over $17 million to fund projects that will improve Great Lakes water quality by preventing phosphorus runoff and soil erosion that contribute to algal blooms.

Texas water district recognized for Eagle Mountain Spillway Dam rehabilitation

The Association of State Dam Safety Officials announced that it has awarded the Tarrant Regional Water District of Texas with the National Rehabilitation Project of the Year Award.

Innovyze named winner of prestigious Esri Partner Conference Award

Innovyze recently announced that it was named the winner of the ArcGIS for Desktop Based Application category of the Esri Partner Conference Awards.

CH2M HILL partnership to deliver safe, clean water supply to Jaipur, India

CH2M HILL in partnership with the Singapore Public Utilities Board and Singapore Cooperation Enterprise, is providing water management leadership services to the Rajasthan state government through Public Health and Environment Department for the city of Jaipur, India.

FOLLOW US ON SOCIAL MEDIA