A Gene That Could Stop Antibiotics Working Found in U.S. Sewage for First Time

An antibiotic-resistant gene has been identified in a U.S. wastewater sample for the first time—indicating that it may have a foothold in the country.

This gene poses a threat to the medicine colistin, a last-resort antibiotic that can be used when other drugs fail.

Mobile colistin resistance, or MCR, genes have been detected in the U.S. before in samples collected from hospital patients. However, scientists have now identified a version of the gene in a sewage sample from a wastewater treatment plant in Georgia.

The researchers, from the University of Georgia, say this indicates that "MCR genes might be becoming established in the USA."

The Food and Drug Administration has not approved the use of colistin in food animals, according to the researchers. This use of colistin is thought to be a key driver of the spread of MCR genes in other countries.

The Georgia study outlines that an MCR gene, called MCR-9.1, was found inside a pathogen called Morganella morganii, which tends to infect hospital patients after operations. It has been linked with other antibiotic-resistant genes before and also appears to be a potential host of the MCR gene, the researchers said.

The gene was identified from a portion of a 1 liter sewage sample that had been collected and returned to the lab for study. The material was spread on agar plates, which allow bacteria colonies to grow, and incubated at 37 degrees Celsius.

The researchers then tested these colonies and found that one showed high resistance to colistin and other important antibiotics. Further investigation revealed that this was Morganella morganii carrying the MCR-9.1 gene.

"It is important to note that intrinsically colistin-resistant bacteria are not routinely screened for MCR and their role in the transmission of these genes is not extensively studied," the report said.

"Therefore, the detection of plasmid-borne MCR in intrinsically colistin-resistant bacteria such as M. morganii highlights an overlooked and novel aspect of MCR epidemiology that should be considered in future investigations in the USA and other countries."

The study, "First report of the mobile colistin resistance gene mcr-9.1 in Morganella morganii isolated from sewage in Georgia, USA," was published in the Journal of Global Antimicrobial Resistance on December 9.

Colistin and Antibiotic Resistance

Colistin is a 50-year-old antibiotic that is increasingly used as a "last-line" therapy to treat certain bacteria when all other options will not work, according to a 2009 review of the drug in the journal Current Opinion in Infectious Diseases.

Antibiotic resistance happens when bacteria and other germs develop the ability to essentially fight back against the drugs designed to kill them.

The process happens naturally, but misuse of antibiotics by humans is accelerating resistance. A growing number of infections are becoming harder to treat because the antibiotics we use to fight them are less effective, according to the World Health Organization.

The WHO says individuals can help prevent the acceleration of antibiotic resistance by never demanding antibiotics if they aren't necessary and preventing infections in the first place with general good hygiene.

Agar plate
Stock photo of a scientist looking at samples. Antibiotic resistance will make some illnesses more difficult to treat. Manjurul/Getty