In the first known study of its kind, Chuanwu Xi of the University of Michigan School of Public Health and his team sampled water containing the bacteria Acinetobacter at five sites in and near Ann Arbor's wastewater treatment plant.
They found the so-called superbugs—bacteria resistant to multiple antibiotics—up to 100 yards downstream from the discharge point into the Huron River. Xi stresses that while the finding may be disturbing, it is important to understand that much work is still needed to assess what risk, if any, the presence of superbugs in aquatic environments poses to humans.
"We still need to understand the link between aquatic and human multiple drug resistant bacteria," said Xi, assistant professor of public health.
Xi and colleagues found that while the total number of bacteria left in the final discharge effluent declined dramatically after treatment, the remaining bacteria was significantly more likely to resist multiple antibiotics than bacteria in water samples upstream. Some strains resisted as many as seven of eight antibiotics tested. The bacteria in samples taken 100 yards downstream also were more likely to resist multiple drugs than bacteria upstream."Twenty or 30 years ago, antibiotics would have killed most of these strains, no problem," he said.
Multiple antibiotic-resistant bacteria has emerged as one of the top public health issues worldwide in the last few decades as the overuse of antibiotics and other factors have caused bacteria to become resistant to common drugs. Xi's group chose to study Acinetobacter because it is a growing cause of hospital-acquired infections and because of its ability to acquire antibiotic resistance.
Xi said the problem isn't that treatment plants don't do a good job of cleaning the water—it's that they simply aren't equipped to remove all antibiotics and other pharmaceuticals entering the treatment plants.
Read full from the University of Michigan,