In 2008, doctors first identified the New Delhi metallo-β-lactamase, or NDM-1, resistance gene in bacteria from a Swedish patient who had been hospitalized in India. The gene makes bacteria immune to almost all β-lactam antibiotics, even drugs of last resort. Infections with bacteria carrying the gene have been seen in patients in Asia, Europe, the U.S., and Australia. Now researchers report that some wastewater treatment plants in China discharge NDM-1 into the environment. Public health experts worry that this release could promote the spread of the troublesome gene.
The study “sounds a huge alarm,” says Jeffrey Duchin, chair of the public health committee of the Infectious Diseases Society of America, who was not involved in the study.
Serious β-lactam-resistant infections, such as the so-called carbapenem-resistant infections, are primarily caused by bacteria found in hospitals. But if NDM-1 were to spread outside hospitals to bacteria that cause urinary tract infections, diarrhea, and other common ailments, these conditions could become untreatable with routine antibiotics. “It would be a disaster,” Duchin says.
Pedro J. J. Alvarez of Rice University, Daqing Mao of Tianjin University, in China, and their colleagues detected the released gene while analyzing water at various treatment stages in two wastewater treatment plants in northern China. The team extracted bacterial DNA from the water samples and used polymerase chain reaction to measure the abundance of NDM-1.
Treated water released by both plants contained thousands of copies of the resistance gene per milliliter (Environ. Sci. Technol. Lett. 2013, DOI: 10.1021/ez400152e). Alvarez says the NDM-1 genes measured in the study could be carried by living bacteria or represent DNA expunged by dead bacteria.
Also, in a laboratory experiment, the researchers showed that bacteria from the treatment plants could pass NDM-1 to bacteria in the environment that did not previously carry the gene.
Alvarez says treatment plants could reduce the risk of environmental contamination by disinfecting water more efficiently before discharge. He and his team are developing a new treatment method that involves ultraviolet radiation and photocatalysts.