Anyone who has gone to the doctor for a bacterial infection such as strep throat (Streptococcal pharyngitis) is likely familiar with antibiotics. The doctor typically prescribes an antibiotic to kill the bacteria and advises patients to take the full course of antibiotics, even if they start to feel better. This is to protect against antibiotic resistance.
However, prescriptions are not the only source of concern for antibiotic resistance. Instead, we must look to the antibiotics consumed by our food—in particular, our livestock. Over 70 percent of antibiotics sold in the United States are given to livestock, including cattle, which translates to significant human health impacts.
What Is Antibiotic Resistance?
For much of human history, bacteria have presented a danger to human health. For example, diseases like the bubonic plague, caused by the bacteria Yersinia pestis, reached pandemic proportions and wiped out large segments of the global population. Fortunately, the development of antibiotics has revolutionized treatments for such bacterial diseases, which means they have not been able to spread as they once did. But this safety is being threatened by the looming possibility of antibiotic resistance.
Like other organisms, bacterial populations adapt and evolve over time. When bacteria are exposed to an antibiotic over a long period of time, they can evolve a resistance to the drug. Initially, bacteria treated with antibiotics will die, but if some bacteria happen to have a genetic mutation that makes them resistant to the antibiotics, those bacteria will continue to survive and multiply. Through a process known as vertical gene transfer, resistant bacteria will reproduce and pass on this resistance to their offspring and create a whole new generation of resistant bacteria.
Bacteria can also pass on antibiotic resistance through a process known as horizontal transfer in which genes can actually be passed between bacteria—including different bacteria species. An enzyme in bacteria known as transposase can cut out the DNA of the resistant bacterium and then move the segment to a circular piece of DNA called a plasmid. The gene can then be transferred via the plasmid to a different bacterium.
The consequences of antibiotic resistance are more than conjecture. Some bacteria have already developed resistance to antibiotics. Notably, methicillin-resistant Staphylococcus aureus, or MRSA—a type of bacteria that causes staph infections—are highly resistant to antibiotics.
Why Are Cattle Given Antibiotics?
Antibiotics are given to farm animals, such as cattle, for some of the same reasons they are given to humans: to treat infections. Disease transmission is particularly concerning in livestock because they are often housed together in close quarters, where there is increased potential for spreading disease. Cattle in particular are susceptible to infections and liver abscesses because they are often fed a corn-based diet despite having evolved to eat grass. Unlike with human medicine, however, antibiotics are often fed to cattle as a preventative measure, rather than as a treatment.
Antibiotics have another unexpected benefit: they allow livestock to grow larger much more quickly than usual. Scientists have yet to discover why this occurs, but it is theorized that the antibiotics kill gut bacteria and allow cattle to digest food more efficiently. This has led many cattle producers to feed livestock low doses of antibiotics for long periods of time in order to garner a greater profit from a single animal, but at the expense of contributing to antibiotic resistance.
How Does this Affect Humans?
Antibiotic resistance in cattle does not only affect the health of the cattle, it impacts people as well because many of the antibiotics given to cattle are also used in human medicine. Eating meat or consuming milk from an animal with antibiotic-resistant bacteria may infect a human with that same resistant bacteria. Salmonella and Campylobacter are among the most common food-borne antibiotic-resistant bacteria. Salmonella dublin is one example of bacteria that can be passed from cattle to humans through the consumption of meat or dairy products.
It is not just animal products that pose a threat to human health either. Antibiotic-resistant bacteria can even make their way into the air, water, and soil. For example, manure from cattle is often used to grow vegetables. If this manure contains antibiotic-resistant bacteria, it can contaminate vegetables and soil as well.
In addition to making it more difficult to treat bacterial infections in humans, the increased use of antibiotics has negative effects on the human microbiome, the ecosystem of bacteria in the gut that keeps us healthy. This can result in short-term opportunistic infections, in which the absence of good bacteria allows bad bacteria to thrive. Alterations to the microbiome can also mean long-term health consequences, such as impaired immunity, and some researchers even suspect that increased exposure to antibiotics ultimately contributes to obesity.
What Can Be Done?
The dangers of antibiotic resistance are being recognized all over the world, and governments are working to take action. Partnerships between governments, cattle producers, and veterinarians can help alleviate antibiotic resistance. Such partnerships implement measures such as reducing the overall use of antibiotics, only using antibiotics prescribed by a veterinarian, and not using antibiotics to enhance production. Also, improving livestock husbandry practices could help reduce the spread of disease and thus the need for antibiotics.
Individual actions can also help prevent the spread of antibiotic resistance. For instance, lowering consumption of meat reduces the risk for infection. Consumers can also look for meat labeled as “antibiotic free” however, this term does not have a unified definition, and the meat may still come from an animal carrying antibiotic-resistant bacteria. It is also recommended to use safe cooking methods such as cooking to the appropriate temperature, separating meats and vegetables, and washing hands.
Halting antibiotic resistance demands a collaborative effort involving many different people, and it is an effort that impacts the medicine we take and the food we eat. But, like the initial discovery of antibiotics, the effort to stop antibiotic resistance will transform human and animal health alike.