A new study suggests clues to overcoming drug resistance in superbugs may lie in understanding why soil bacteria, despite having many drug-resistant genes, seem reluctant to share them.

The ability of bacteria to swap genes is known to be an important driving force in the rise of superbugs - microbes that are becoming increasingly resistant to drugs designed to kill them. The rise of superbugs poses a serious threat to global public health. The World Health Organization recently warned that common infections may become killers unless we act now.

According to a recent threat report from the Centers for Disease Control and Prevention, around 2 million Americans every year become infected with drug-resistant bacteria, and at least 23,000 die as a result of such infections. Many more die from other conditions that became complicated because of drug-resistant infection.

Antibiotic resistance now accounts for $20 billion of annual health-care costs and 8 million additional hospital treatment days in the US.

Soil bacteria have a large armoury of antibiotic-resistant genes

It is thus alarming to discover that bacteria that live naturally in the soil have a large armoury of genes to fight off antibiotics. But a new study led by Washington University School of Medicine (WUSTL) in St. Louis, MO, and published in the journal Nature, reveals that this large armoury is not poised to contribute to antibiotic resistance in infectious bacteria.

Senior author Gautam Dantas, assistant professor of pathology and immunology at WUSTL, hopes by studying the surprising lack of sharing of drug-resistant genes in soil bacteria, they may find ways to reduce gene sharing in infectious bacteria, and also, as he explains:

"Soil bacteria have strategies for fighting antibiotics that we're only just starting to learn about. We need to make sure the genes that make these strategies possible aren't shared with infectious bacteria, because they could make the problem of drug-resistant infections much worse."

The majority of drugs used to combat infection today come from soil microbes. For example penicillin, the first successful antibiotic, originates from the soil fungus Penicillium.

But unfortunately, widespread use of penicillin and other antimicrobial drugs has driven bacteria to evolve ways of resisting them.

Resistance genes in soil bacteria 'not poised' for sharing with pathogens

Scientists studying antibiotic resistance in bacterial DNA have identified patterns of genetic code that enable the microbes to share resistance genes. If a gene sits close to these "mobility elements," then it is readily shared with other bacteria.

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Scientists studying antibiotic resistance in bacterial DNA have identified patterns of genetic code that enable the microbes to share resistance genes.

Prof. Dantas and colleagues analyzed the DNA of bacteria found in 18 soil samples from agricultural and grassland sites in Minnesota and Michigan.

Using a technique they helped to develop, they identified around 3,000 antibiotic resistance genes in the soil bacteria. However, they were not situated close to mobility elements in the bacteria's DNA.

They also found that individual drug-resistance genes were closely linked with particular bacteria, suggesting they were not readily shared among species.

"We suspect that one of the primary factors that drives the sharing of antibiotic resistance genes is exposure to new antibiotics," explains Prof. Dantas. "Because soil bacteria need many thousands of years to develop new antibiotics, the bacteria in that community don't encounter these threats anywhere near as often as disease-causing bacteria, which we regularly treat with different antibiotics."

He says they were happy to discover that antibiotic resistance genes from soil bacteria are not poised to jump suddenly into infectious bacteria. But he warns we need to do everything we can - from the way we treat infections to the way we manage environments that harbor bacteria - to keep the odds in our favor.

Funds for the study came from a number of organizations, including the National Institutes of Health, the Children's Discovery Institute, the International Center for Advanced Renewable Energy and Sustainability at Washington University, and the National Academies Keck Futures Initiatives.

Meanwhile, Medical News Today recently learned how new agents may revitalize antibiotics to fight superbugs. A study published in the Journal of the American Chemical Society showed it may be possible to fight superbugs with conventional antibiotics by pairing the drugs with a new class of metal-based agents called metallopolymers, which revitalize their potency.