Antibiotic drugs can be a lifesaver for anyone suffering from a bacterial infection such as meningitis or pneumonia. Antibiotics kill Bacteria, and thus help fight infection. But some types of bacteria can develop a resistance to these drugs, while others not only become resistant but also utilize antibiotics as a source of food.

Until now, scientists have not fully understood how drug resistant bacteria manage to safely consume antibiotics, but a study that was published in the scientific journal Nature Chemical Biology earlier this year reveals important steps in this process. The study's findings could help establish new methods to remove antibiotics from soil and water, thus ridding the environment of antibiotic contaminants which promote drug resistance, undermining our ability to cure bacterial infections effectively.

"Ten years ago we stumbled onto the fact that bacteria can eat antibiotics, and everyone was shocked by it," said senior author Gautam Dantas, an associate professor of pathology and immunology, of molecular microbiology, and of biomedical engineering at the Washington University School of Medicine, St. Louis. "But now it's beginning to make sense. It's just carbon, and wherever there's carbon, somebody will figure out how to eat it. Now that we understand how these bacteria do it, we can start thinking of ways to use this ability to get rid of antibiotics where they are causing harm."

When these resistant bacteria get into soil, waterways and ultimately drinking water sources, they can cause antibiotic resistance in people who are exposed to them. Antibiotic resistance is an increasingly common problem that adversely affects medical treatment of infectious diseases, eroding the advances made in medical care since antibiotics were discovered, and ultimately putting people's lives at risk.

Modern day agricultural and industrial practices which saturate the environment with antibiotic drugs are fueling the growth of antibiotic resistance. In China and India, the two largest producers of antibiotic drugs, pharmaceutical companies often discharge antibiotic-laden wastewater into local waterbodies. Back home in the US, farmers routinely feed antibiotics to their livestock to help them grow healthy and strong, resulting in animal waste that is laded with these drugs.

Because bacterial communities readily exchange genetic material, when soil and water become polluted with antibiotics, bacteria living in these habitats respond by sharing their antibiotic resistant genes with their neighbors.

The researchers wanted to gain a clearer understanding of how some bacteria in the environment are not only resistant to antibiotics, but also feed on the drugs. They examined four types of soil bacteria that were distantly related and which flourished on a diet consisting solely of penicillin — the first antibiotic ever discovered, which until recently was widely used but is prescribed less often now due to antibiotic resistance. They found three sets of genes that were activated when the bacteria consumed penicillin, but which became inactive when the bacteria consumed sugar. The three genetic sets correspond to the three steps the bacteria take to convert what should be a lethal drug into a nutritious meal.

According to the authors, "all of the bacteria start by neutralizing the dangerous part of the antibiotic. Once the toxin is disarmed, they snip off a tasty portion and eat it."

Gaining a clearer understanding of the steps the bacteria take to convert antibiotics into a source of food may help scientists bioengineer bacteria and put them to work ridding soil and waterbodies that are contaminated with antibiotics in an effort to combat the rise in drug resistance.

Because soil dwelling bacteria that typically consume antibiotics are not so easy to work with, the researchers suggest that with some genetic tweaking, "a more tractable species such as E. coli potentially could be engineered to feed on antibiotics in polluted land or water."

"With some smart engineering, we may be able to modify bacteria to break down antibiotics in the environment," said Terence Crofts, a post-doctoral researcher and primary author of the study.

While bacteria are effective at removing antibiotics from soil, their rate of consumption is slow. Consequently, if we have any hope of eradicating antibiotics from hotspots such as sites located near sewage plants' or pharmaceutical manufacturers' discharge outlets, any bioengineering project with this goal in mind would need to encourage the bacteria to consume antibiotics faster.

"You couldn't just douse a field with these soil bacteria today and expect them to clean everything up," Dantas said. "But now we know how they do it. It is much easier to improve on something that you already have than to try to design a system from scratch."

Journal Reference

T.S. Crofts, et al. Shared strategies for β-lactam catabolism in the soil microbiome. Nature Chemical Biology. Vol.14, 556-564; (2018)