Bacteria Resistant To Last-Resort Antibiotic Found In Georgia Sewage

Scientists did not realise the gene was circulating the USA. Image Credit: Jarun Ontakrai/Shutterstock.com

A gene that grants bacteria resistance to an important last-resort antibiotic has been discovered circulating in the sewage water of Georgia.

Mcr-9 is a gene found in gram-negative bacteria, such as Salmonella and E. Coli, and is part of the mobile colistin resistance (mcr) gene family that enables bacteria to become resistant to colistin. Colistin is an antibiotic critical in the fight against multidrug-resistant bacterial strains, often used against infections that do not respond to other antibiotics.

If multidrug-resistant strains were to gain an MCR gene, it would mean one of our last remaining weapons against antibiotic resistance is no longer effective. 

As such, scientists have been closely monitoring the mcr family, and until now, thought it was not prevalent across the USA. However, new research from the University of Georgia's Center for Food Safety (CFS) has made a damning discovery – isolates from sewage in Georgia have returned positive for mcr-9.1. Furthermore, these isolates are resistant to colistin, as well as a host of other important antibiotics. 

The research suggests mcr-9 could be far more widespread than previously thought, calling for significantly more investigation in the establishment of MCR variants in the USA. A shortened version of the research has been published in the Journal of Global Antibiotic Resistance.  

Colistin is used as an agricultural antibiotic by many countries, and this has been attributed as a primary driver for colistin resistance in bacteria to date. It has since been banned in the USA, in an attempt to curb the possibility of MCR spreading through the country, but it is unclear how successfully those measures were.  

In this study, the scientists isolated samples from sewage in Georgia, following reports that bacteria carrying mcr genes were found in New York, Connecticut, New Jersey, and Michigan.

Taking a large amount of sewage and returning it to the lab to isolate the bacteria within, the researchers discovered Morganella morganii (a gram-negative bacteria found as normal flora within the human and animal gut) with an mcr-9.1 gene. When tested on antibiotic plates, it showed high resistance to colistin, plus many other important antibiotics commonly used against bacterial infection. 

According to the authors, this marks the first sighting of mcr-9.1 in M. morganii, and the first time mcr has ever been isolated from a sewage sample – and that is bad news for scientists concerned about antibiotic resistance. They now call for a significant collaboration to tackle the crisis, which is listed by the WHO as "one of the top 10 global public health threats facing humanity." 

"If we don't tackle it right now, we are jeopardizing human and animal medicine as we know it and that can have huge repercussions on health and the economy," said Issmat Kassem, assistant professor at College of Agricultural and Environmental Sciences, in a statement to Phys Org.

"It's a dangerous problem that requires attention from multiple sectors for us to be able to tackle it properly." 

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