The evolution of "superbug" methicillin-resistant Staphylococcus aureus, or MRSA, is a classic example of how the antibiotic miracle has turned into a disaster due to misuse and overuse of antibiotics. Being resistant to methicillin and other commonly prescribed antibiotics, MRSA infections are difficult to treat.
MRSA, which is a variant of the common bacterium Staphylococcus aureus, mostly affects patients in hospitals and other healthcare settings, and these are known as hospital-acquired MRSA. But since the late-1990s, MRSA infections are said to have become increasingly common among otherwise healthy people in the community who have no contact with the healthcare settings. The MRSA infections acquired outside of hospital settings are known as community-acquired MRSA or CA-MRSA.
What has not been fully understood yet is the potential environmental sources of the community-acquired MRSA. As a first step towards this goal, researchers at the University Of Maryland School Of Public Health investigated two Mid-Atlantic and two Midwestern wastewater treatment plants, or WWTPs, for the presence of the antibiotic-resistant bacteria. It is to be noted that the treated effluent discharged from these plants is reused as "reclaimed wastewater" in spray irrigation activities.
An analysis of raw sewage samples of all the four plants has revealed the presence of MRSA, as well as a related pathogen, methicillin-susceptible Staphylococcus aureus, or MSSA. However, the percentage of MRSA- and MSSA-positive samples decreased as treatment progressed, say the researchers.
But that said, in one of the WWTPs that did not regularly use chlorination for treatment, bacteria was detected even in the treated water leaving the plant.
According to the researchers, 93 percent of the MRSA strains and 29 percent of MSSA strains that were isolated from the wastewater were resistant to two or more classes of antibiotics, including several of the FDA-approved medications for treating MRSA infections.
Given the increasing use of reclaimed wastewater, the findings of the study raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater, says Rachel Rosenberg Goldstein, the study's first author.
The University of Maryland-led study is the first to document the environmental source of superbug MRSA in the U.S. Swedish researchers have already identified the presence of MRSA in WWTPs in Sweden.
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