The recent discovery in an American patient of a “superbug” resistant to colistin, an antibiotic of last resort, is currently rocking the medical profession. This resistance gene has now been found in several U.S. communities just a few weeks after its discovery at the end of May at Walter Reed Army Medical Research Center. The rapid movement of this gene into new populations illustrates just how easily bacteria can share genes that are advantageous to them.
Did you know that 70 percent of all medically important antibiotics used in the United States are given to farm animals that are not even sick? For decades, it has been common practice to administer low doses of the same antibiotics used in human medicine to livestock for growth promotion.
Giving low doses to the entire herd on a regular basis is known to be the fastest way to produce bacterial populations that can resist antibiotics. This is why the European Union banned the prophylactic use of antibiotics in 2011.
Despite the importance of this problem, a bill introduced in Maryland’s General Assembly this year to limit the use of medically important human antibiotics in farm animals did not even get a vote in either the House or the Senate. Sponsored by Sen. Paul Pinsky (D-Prince George’s) and Delegate Shane Robinson (D-Montgomery), this bill would have been a meaningful step in halting a practice that is known to endanger human health.
After many years of warnings from health professionals about the dangers of this practice, the FDA released voluntary guidelines in 2015 for reducing the use of antibiotics in livestock. The FDA guidelines ban the use of antibiotics for growth promotion, but there is a major loophole — they allow livestock producers to continue to administer regular low doses of human antibiotics to animals that aren’t sick for the purpose of “disease prevention.”
Is it a coincidence that the regimens of antibiotics used for disease prevention are virtually the same as those previously used for growth promotion? No medical doctor would prescribe antibiotics to human patients for disease prevention — they know that the risk of antibiotic-resistant bacteria is simply too great. Yet the livestock industry finds this practice useful; in many cases, animals are crowded into unsanitary conditions, and the growth promotion that occurs as a side effect of “disease prevention” allows animals to be more quickly brought to market.
We agree that if individual animals in a commercial herd or flock are sickened with a bacterial infection, they should have access to veterinary care and appropriate use of antibiotics. We also agree that it is appropriate to use antibiotics in the event of a major disease outbreak.
However, we note that such outbreaks may be the result of crowded living conditions in many Concentrated Animal Feeding Operations (CAFOs).
The routine use of human antibiotics in healthy livestock is a public health risk for humans for several reasons. First, unlike the animals with which most of us are familiar, bacteria do not have to inherit genes for traits (like antibiotic resistance) from parents — they can pass around small bits of DNA (called plasmids) that carry “useful” genes like those for antibiotic resistance or the ability to digest different food sources.
These plasmids can even be exchanged between distantly related bacterial species. Bacteria also have the amazing ability to take up DNA from other bacteria that have died in the vicinity. Because of these unusual abilities, if just one bacterial cell has a gene to resist an antibiotic, it can share it with all of the other bacteria in the host organism and its environment.
Thus, when antibiotic-resistant bacteria appear in a livestock herd, they can pass around the gene for resistance to any other bacteria in the neighborhood. This puts farmworkers and meat packers at tremendous risk. Farmworkers and farm families in other states have also been found to harbor bacteria resistant to the antibiotics fed to their livestock.
Secondly, bacteria from livestock operations move directly into the human community. In Maryland, manure from animals fed a routine diet of antibiotics may be spread on fields as fertilizer for crops, potentially contaminating our food with antibiotic resistant bacteria.
In addition, runoff from these fields allows bacteria from the manure to contaminate our streams and the Bay. A recent study from UMD’s School of Public Health reports an elevated level of salmonella infections on Maryland’s Eastern Shore relative to other parts of the state. This was attributed to contamination of recreational waters and even wells during flooding after severe rains by bacteria from livestock operations. Although most of these bacteria just make people sick, some will resist the antibiotics that will allow them to quickly recover.
This is a problem for all of us.
Medical professionals are becoming increasingly concerned that the rampant spread of antibiotic resistant bacteria will soon return us to the pre-antibiotic era, when even the simplest bacterial infection often proved deadly.
The medical community is working hard to use antibiotics judiciously in humans. Consumer demand is prompting companies like Perdue to phase out antibiotics in their products. We can’t wait much longer for the rest of the agricultural community to follow suit.
We urge policymakers at the state and federal level to take this issue seriously and eliminate the use of medically important human antibiotics in farm animals that are not sick.
Dr. Sara Via is a professor of biology and entomology at the University of Maryland, College Park, and a member of Chesapeake Physicians for Social Responsibility. Betsy Nicholas is the executive director of Fair Farms, a campaign for healthy food, land and waterways sponsored by Waterkeepers Chesapeake.