New research has demonstrated an association between heavy metal and radioactive soil pollution and the resistance of bacteria living in that soil to the antibacteria.
Appearing in the journal Microbial Biotechnology, the study adds weight to earlier results. Indeed, previous research suggests that they also evolve antibacterial properties because bacteria react to heavy metal and radioactive emissions.
Resistance to antibiotics is an important global health issue. This is described by the World Health Organization (WHO) as “one of the greatest threats to global health, food security and development today.”
People rely on antibiotics to treat bacterial infections. They are vital to modern medicine, and have saved innumerable lives. Popular infections and injuries without antibiotics can be fatal.
Even humans use antibiotics for food. For example, farmers routinely give animals antibiotics to increase yields.
But bacteria can develop antibiotic resistance, making specific antibiotics less effective or completely useless.
While antibacterial resistance occurs naturally, the process is made more probable by human behaviour. Overuse of antibiotics is the primary driver of antibacterial resistance in both humans and animals.
When people unnecessarily or indiscriminately use antibiotics, there’s a greater risk that bacteria will become immune to them.
Market pressures, for example, promote extensive use of antibiotics in livestock, whether or not the animals have bacterial infections.
This indiscriminate use increases the chance that bacteria will become resistant to antibiotics, rendering the drug ineffective when bacterial infections occur in humans or other animals.
The role of pollution
In addition to the indiscriminate and improper use of antibiotics, there is also evidence to indicate that certain pollutants that inculcate antibiotic activities.
According to the corresponding author of the study Jesse C. Thomas IV: “Overuse of antibiotics in the environment adds additional selection pressure to microorganisms which accelerates their ability to resist multiple classes of antibiotics. But antibiotics aren’t the only pressure source for selection.
He adds, “Many bacteria have genes that work on multiple compounds that would be toxic to the cell at the same time, and that includes metals.”
In healthy soil bacteria exist in abundance. Up to 1 billion bacteria can occur in a teaspoon of soil, according to the United States Department of Agriculture. This represents up to one ton of bacteria per acre of soil.
These bacteria can gain resistance when exposed to harmful pollutants, such as heavy metals. But there is also evidence to suggest that the bacteria may develop resistance to antibiotics in developing this resistance to pollutants at the same time.
The researchers decided to explore the relationship further in the recent report. To do so, they focused on an area of the United States that was once the location of a nuclear weapons production facility: the Savannah River Site, in the upper South Carolina coastal plain.
From 1950 to the 1980s the nuclear weapons production facility was active and involved numerous heavy metal industries across the Savannah River Region.
“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 contained significant pollutants such as heavy metals and radionuclides.
The researchers collected samples from four sites in this sector:
- 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
Then the researchers studied the genetic composition of the bacteria present at each site in the soil.
The researchers found that areas with large concentrations of heavy metals, radionuclides, or both had less soil bacteria diversity than the reference site.
They identified bacteria with genes in all four sites, including the reference site, which rendered them both immune to pollutants and antibacterial drugs.
But the scientists observed an increased abundance and variety of antibiotic-resistant and metal-resistant genes at sites with large levels of emissions.
Bacteria including Acidobacteriaoceae, Bradyrhizobium, and Streptomyces all displayed genes that made them immune to vancomycin, bacitracin, and polymyxin, which are antibiotics used by doctors to treat bacterial infections.
Researchers point out people should be careful when interpreting their results.
While they found a clear link between soil contaminants and antibacterial resistance, they note that there are likely to be other confounding factors at function. This may exacerbate a potentially causal relationship between soil pollution and resistance to the bacteria.
However, their study supports other research studies which have come to similar conclusions, and it makes clear the importance of more research in this field.