Antibiotic-resistant bacteria are already directly responsible for the deaths of an estimated 1.27 million people every year, and these challenging infections contribute to the deaths of millions more, according to the World Health Organization. This problem will likely only get worse in the coming years, as bacteria can easily share resistance genes with one another and evolve new ways to evade the effects of drugs. Scientists are searching for new antibiotics that are safe and effective, but it can be very difficult to develop those medications.
New research has highlighted how soil bacteria can add to the problem of antibiotic resistance. Bacteria compete with one another, and many actually generate compounds that kill other microbes. That also means that bacteria have ways to fight those antimicrobial compounds. Antibiotic-resistance genes can exist on tiny bits of DNA known as plasmids, and the world's soils are packed with ARGs that can be shared among microbes.
Humans have had a huge impact on land around the world, and the disruption of ecosystems can facilitate the movement of ARGs, making it even easier for soil microbes to share them, and cause infections that are tough to treat. When ARGs end up in a bacterial pathogen, serious infections that can't be eliminated may happen.
In a new study reported in Nature Communications, scientists have shown that when a bacterium acquires ARGs, they can quickly move them to another microbe. Knowing more about the transmission of ARGs may help us reduce their spread.
Listeria monocytogenes bacteria naturally lives in soil, but it can also get into food and cause an illness known as listeriosis. While this illness is not always severe, it can be a major problem for people with weaker immune systems, and listeriosis can have fatality rates that are as high as 30 percent. Listeria can also spread ARGs.
"Soil is an important reservoir of resistant bacteria and ARGs," noted corresponding study author Jingqiu Liao, an assistant professor at Virginia Tech. "Environmental factors can amplify ARGs by creating conditions that promote the survival, spread, and exchange of these genes among bacteria."
The researchers analyzed the genomes of about 600 listeria microbes that were obtained from soils around the US to learn more about how ARGs spread. This effort revealed five primary ARGs in listeria, and bacteria can easily pass them along to other microbes.
Various soil characteristics were linked to the spread of ARGs. Soils that have high aluminum levels boost ARG spread, possibly because bacteria that live there are under pressure, and prefer to hang onto those protective genes. Soils carrying high levels of magnesium were found to reduce ARG levels. There were more ARGs in forested ecosystems, potentially because wildlife carry those ARGs into that environment. Agricultural areas were very disruptive to soil and the microbes they host, which had various influences on ARGs.
The study authors noted that when people come into contact with soil, it's important for them to maintain good hygiene and sanitation to prevent the spread of infection or ARGs. The researchers added that it is important to keep soil healthy, not only for the sake of the environment, but also to prevent the spread of disease in people.
"Establishing a fundamental understanding of the ecological drivers of these bacteria in the soil could help us better understand the emergence, evolution, and spread of antibiotic resistance," said Liao. "This is an urgent, global public health threat."
Sources: Virginia Tech, Nature Communications