The right chemistry: Farmers are making a dangerous gamble by using too many antibiotics


Antibiotics are very effective, but they are not perfect, and the remaining bacteria can cause problems if they enter our stomach.

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It is perhaps the most important class of drugs ever introduced. Antibiotics are the best weapon we have in the fight against pathogenic bacteria. This is a fight we cannot afford to lose. But it can happen if the bacteria become resistant to antibiotics.

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Although antibiotics are very effective at killing bacteria, they are not perfect. Some bacteria are more resistant than others and when a population of bacteria is exposed to an antibiotic, some survive. These will then pass on the genetic machinery that allowed them to survive to their offspring, thus also making them resistant to the antibiotic in question. Basically, whenever an antibiotic is used, there is a chance of developing a strain of insects that is resistant to that antibiotic. Consequently, a subsequent infection caused by this strain will be resistant to antibiotic treatment. The moral here is that antibiotics should be used appropriately and not lightly, which raises the topic of their use in animal agriculture.

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Like humans, cattle, pigs, poultry and fish can suffer from bacterial infection and require treatment with antibiotics. These are usually administered in the animals’ food or water on the advice of a veterinarian who specializes in bacterial diseases of farm animals. No medical intervention is without risk and with antibiotics we have the double problem of residues and resistance. A course of antibiotics can result in traces of residues of the drug found in the meat after slaughter and these can then end up in our bodies when that meat is eaten. The issue here is not toxicity, but the fear that the drug might kill susceptible bacteria and allow resistant microbes to thrive. This risk is very low since antibiotic residues in meat are very strictly regulated and treated animals can only be slaughtered after the specific time required to remove the residues.

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A bigger problem than residue is the direct passage of resistant bacteria to people. It is inevitable that an animal treated with antibiotics develops resistant bacteria which can then be transmitted to humans through contact with animal feces. Farm workers can become infected and then spread the disease. Meat can also be contaminated during slaughter, and traces of feces can be found on meat sold in stores. Although heat can kill most bacterial contaminants, improper cooking or mishandling before cooking can contaminate surfaces and possibly other uncooked foods. Of course, we don’t want to eat meat from sick animals either, so eliminating antibiotics altogether isn’t the answer. Emphasis must be placed on the appropriate and judicious use of these life-saving drugs.

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What constitutes misuse? Giving animals antibiotics to make them gain weight faster would be one. Although penicillin was discovered by Alexander Fleming in 1928, it was not until the 1940s that it became widespread thanks to the work of doctors Howard Walter Florey and Ernst Boris Chain, who succeeded in isolating the drug from penicillium mold and have developed methods to produce it on a large scale. It also sparked a search by pharmaceutical companies for other antibiotics, and in 1945 researchers at Lederle Laboratories isolated chlortetracycline from a soil sample taken from a field at the University of Missouri. While testing this new drug, they noted that it caused the animals to gain weight. This discovery was quickly turned into a commercial enterprise, namely the sale of antibiotics to farmers who wanted to increase their profits by bringing their animals to maturity more quickly. The concept of antibiotic resistance was not even on the horizon at the time and the addition of antibiotics to animal feed became widespread.

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At the start of the 21st century, the problem of resistant bacteria promoted by the use of antibiotics in humans and animals was recognized and in 2006 the European Union banned the use of antibiotics as growth promoters in animals. A decade later, Canada and the United States followed suit. With companies no longer able to sell antibiotics to farmers as growth promoters, they have turned to promoting low-dose antibiotics in animal feed as a means of disease prevention. As a result, there was no significant reduction in animal exposure to antibiotics. Growing concerns about bacterial resistance as well as consumer resistance to buying meat that may contain antibiotic residues have now moved farmers away from the prophylactic use of antibiotics.

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Modified practices may also reduce the need for such prophylaxis. For example, piglets are weaned naturally around the age of 3-4 months, but in “factory farms”, they are often weaned after one month. In this case, they have not had sufficient access to antibodies from breast milk, which makes them more prone to gastrointestinal illnesses and post-weaning diarrhea. Early weaning also interferes with the development of a healthy microbiome, the proper balance of healthy and harmful bacteria in the animal’s gut. A disrupted microbiome can lead to later disease requiring antibiotics. The poultry microbiome is also affected by intense farming practices. Chicks absorb microorganisms through the pores of the egg during brooding, but in modern husbandry the eggs are removed from the mother and cleaned on the surface. Plus, once the chicks hatch, they don’t have a chance to come out and peck the ground with all kinds of bacteria that would diversify their microbiome and prevent disease. Again, farmers are turning to prophylactic antibiotics for help. Shame.

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While antibiotic residues in meat are unlikely to impact human health, the generation of antibiotic-resistant bacteria in animals poses a threat to humans. That’s why meat labeled “never antibiotics” enjoys increased sales despite a higher cost. However, it should be emphasized that the misuse of antibiotics in humans presents a much greater risk than their use in animals. Pushing doctors to prescribe antibiotics when they are not indicated is tantamount to crying wolf. If a wolf really comes to the door, then the cries will bring no help.

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Joe Schwarcz is director of the Office of Science and Society at McGill University ( He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3-4 p.m.

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