New research has identified an association between heavy metal and radioactive soil pollution and the antibacterial resistance of bacteria living in that soil.

The research, which appears in the journal Microbial Biotechnology, adds weight to earlier findings. Indeed, previous research suggests that because bacteria adapt to heavy metal and radioactive pollution, they also develop antibacterial properties.

Antibiotic resistance is a major global health crisis. The World Health Organization (WHO) describe it as “one of the biggest threats to global health, food security, and development today.”

Humans depend on antibiotics to fight bacterial infections. They are crucial for modern medicine and have saved countless lives. Common infections and injuries can be fatal without antibiotics.

Humans also use antibiotics for agriculture. For instance, farmers routinely give antibiotics to animals to maximize yield.

However, bacteria are able to develop resistance to antibiotics, rendering particular antibiotics less effective or completely useless.

Although antibacterial resistance occurs naturally, human behavior makes the process more likely. The primary driver of antibacterial resistance is the overuse of antibiotics in both humans and animals.

When people use antibiotics inappropriately or indiscriminately, there is a greater chance that bacteria will become resistant to them.

For example, market pressures encourage the widespread use of antibiotics in farms, whether the animals have a bacterial infection or not.

This indiscriminate use increases the chance that bacteria will become resistant to antibiotics, making the medications ineffective when humans or other animals do develop bacterial infections.

The role of pollution

Alongside the indiscriminate and inappropriate use of antibiotics, there is also evidence to suggest that certain pollutants can inculcate antibacterial resistance.

According to corresponding study author Jesse C. Thomas IV: “The overuse of antibiotics in the environment adds additional selection pressure on microorganisms that accelerates their ability to resist multiple classes of antibiotics. But antibiotics aren’t the only source of selection pressure.”

He adds, “Many bacteria possess genes that simultaneously work on multiple compounds that would be toxic to the cell, and this includes metals.”

Bacteria occur in abundance in healthy soil. According to the United States Department of Agriculture, there can be up to 1 billion bacteria in a teaspoon of soil. This equates to up to a ton of bacteria per acre of soil.

With exposure to harmful pollutants such as heavy metals, these bacteria can develop resistance. However, there is also evidence to suggest that in developing this resistance to pollutants, the bacteria may, at the same time, develop resistance to antibiotics.

Nuclear site

In the recent study, the researchers wanted to further explore this relationship. To do so, they focused on an area of the U.S. that was once the site of a nuclear weapons production facility: the Savannah River Site, in the upper coastal plain of South Carolina.

The nuclear weapons production facility was active from 1950 to the 1980s, and it involved various heavy metals industries throughout the Savannah River Site.

“Over the years, a combination of routine operations, improper disposal practices, and incidental spills contributed to the release of organic and inorganic waste into this environment.”

– Jesse C. Thomas IV, et al.

This waste included serious pollutants, such as heavy metals and radionuclides (radioactive particles).

The researchers took samples from four sites in this area:

• a site that was relatively pristine, which the team used as a reference site
• a site with a preponderance of heavy metals
• a site with a preponderance of radionuclides
• a site that had a combination of heavy metals and radionuclides

The researchers then analyzed the genetic makeup of the bacteria they found in the soil at each site.

Correlation identified

The researchers found that the areas that had significant amounts of heavy metals, radionuclides, or both exhibited less diversity of soil bacteria than the reference site.

Throughout all four sites, including the reference site, they found bacteria with genes that made them resistant to both pollutants and antibacterial drugs.

However, at sites with significant amounts of pollution, the scientists found an increased abundance and variety of antibiotic resistant and metal resistant genes.

Bacteria such as Acidobacteriaoceae, Bradyrhizobium, and Streptomyces all exhibited genes that made them resistant to vancomycin, bacitracin, and polymyxin, which are antibiotics that doctors prescribe to treat bacterial infections.

Causation?

The researchers point out that people should interpret their findings with caution.

Although they found a strong correlation between soil pollutants and antibacterial resistance, they note that other confounding factors are likely to be at play. This may complicate a potentially causal relationship between soil pollution and antibacterial resistance.

Nevertheless, their study backs up other research studies that have reached similar conclusions, and it makes clear the value of further research in this area.

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