Researchers have detected the building blocks of superbugs—bacteria resistant to the antibiotics used to fight them—in the environment near large factory farms in the United States.
An investigation conducted by global animal welfare non-profit World Animal Protection (WAP) identified what are known as “antibiotic resistance genes” (ARGs) in waterways and soils near these farms that could pose a significant threat to public health, according to a report.
In October 2020, investigators took 45 water samples and 45 soil samples from eight sites in eastern North Carolina both downstream and upstream of industrial pig farms. These samples were then analyzed to identify whether 23 target ARGs were present.
The area from where the samples were taken features a heavy concentration of large pig farms, which discharge waste into waterways and spread pig waste on local crop fields.
Factory farms—where large numbers of animals are confined to cages or barren concrete pens—routinely use antibiotics to mask poor welfare conditions and prevent stressed animals from getting sick. But this overuse of antibiotics can lead to the emergence of superbugs, which are considered one of the most significant global health threats.
The WAP researchers found that all the water and soil samples they tested returned a positive result for at least one ARG. In addition, 92 percent of samples displayed positive results for three or more different ARGs.
The presence of ARGs in the samples does not definitively confirm that antibiotic resistant bacteria were present, but it does indicate the genetic potential for resistance.
“ARGs are genetic elements that allow a bacteria not to be as easily killed by a particular type of antibiotic that it previously had been sensitive to,” Michael Hansen, senior scientist on the WAP report told Newsweek.
“ARGs can occur naturally or can be created via mutations. In addition, these ARG often occur on mobile genetic elements, called a plasmid, which allow them to be readily swapped between bacteria.”
Essentially, antibiotic resistant bacteria originating on farms can spread their resistance genes to harmful bacteria already present in the surrounding environment, with the genes persisting beyond the viability of the bacteria themselves.
“When antibiotics are used, they tend to kill the bacteria that are sensitive to them, so that the surviving bacteria are less sensitive to the antibiotic because the population as a whole has become more resistant to that antibiotic. This means that a higher level of antibiotic is needed to kill those bacteria.”
Bacteria originating on farms that are still susceptible to antibiotics can then pick up resistance to important drugs if ARGs are widely present in the environment.
Hansen said the use of antibiotics on farms often leads to various bacteria releasing plasmids with antibiotic resistance genes on them.
As these plasmids move between bacteria, they can pick up more ARGs, so that certain plasmids may contain numerous ARGs conferring resistance to three or more classes of antibiotics. Some plasmids have five or more ARGs on them. Superbugs are defined as bacteria that are resistant to three or more classes of antibiotics.
According to the report, the presence of ARGs in the environment around these farms suggests that they may be playing a significant role in the spread of antibiotic resistance to the environment, while placing nearby communities at risk.
“Bacteria carrying these genes can reach people via several pathways,” Cameron Harsh, Farming Campaign Manager with World Animal Protection, U.S., told Newsweek.
For example, manure stored in lagoons or sprayed on fields can leech into groundwater and public waterways. Particulate matter released into the air can settle on the soil and vegetation nearby. Meanwhile, farmworkers, insects, rodents, wild birds, and farmed animals headed to slaughter may all carry ARGs or superbugs with them.
Harsh said the results of the report raise “concerns that multi-drug resistance is common in this environment. Multi-drug-resistant bacteria pose significant health threat as they are able to survive treatment with several antibiotics. Genes indicating resistance to critically important medicines were also found in several samples.”
Genes conveying resistance to a class of antibiotic drugs known as tetracyclines were identified in nearly all the samples taken for the study.
“Tetracycline-resistance genes have been detected in some previous studies testing in the region, but the high rate of positive results is particularly significant,” Harsh said. “We know that the pig industry is the largest market for tetracycline antibiotics sold to farmed animals in the U.S., and farmer surveys have indicated frequent reliance on these drugs.”
Harsh said that surveillance of antibiotic resistant bacteria occurs in human health settings on certain retail meats, and on farmed animals at slaughter in the United States. But the monitoring of resistant bacteria in the environment at this time is limited.
Superbugs already kill seven hundred thousand people around the would every year, and experts predict that this figure will rise to 10 million deaths annually if nothing is done to address the issue, causing an estimated $100 trillion in global economic losses.
The WAP investigation also conducted similar testing of water and soil samples collected near factory farms in farms in Canada, Spain, and Thailand. These studies also detected the widespread presence of ARGs.
In light of the report, Harsh said factory farms can reduce the risk of contaminating the environment with antibiotic resistant elements by reducing their use of antibiotics, although this must be accomplished alongside improvements to the welfare and living conditions for the animals.
“Raising animals with more space, with enrichments in their pens like straw for pigs and perches for chickens, and with more robust genetics—instead of the high-growth genetics of conventional breeds—are all management practices that can reduce reliance on antibiotics and provide farmed animals with good lives,” he said.
“The U.S. government should also set regulations requiring reduced use of antibiotics in farmed animals, not just medically important antibiotics, and phase out use for disease prevention.”