They are perhaps the most important class of drugs ever introduced. Antibiotics are the best weapon we have in the fight against disease-causing bacteria. That is a fight we cannot afford to lose. But that may happen if bacteria become resistant to antibiotics.
While antibiotics are very effective at killing bacteria, they are not perfect. Some bacteria are hardier than others and when a population of bacteria is exposed to an antibiotic, some survive. These will then pass the genetic machinery that allowed them to survive on to their offspring, thereby rendering these resistant to the antibiotic in question as well. Basically, every time an antibiotic is used, there is a chance of developing a strain of bugs resistant to that antibiotic. As a consequence, a subsequent infection caused by that strain will be resistant to antibiotic treatment. The moral here is that antibiotics must be used appropriately, not frivolously, which brings up the topic of their use in animal agriculture.
Like humans, cattle, pigs, poultry and fish can suffer from bacterial infection and require treatment by 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 risk-free, and with antibiotics we have the dual problems of residues and resistance. A course of antibiotics can result in trace residues of the drug found in the meat after slaughter and these can then find their way into our body when that meat is consumed. The issue here is not toxicity, but concern that the drug may wipe out susceptible bacteria and allow resistant microbes to thrive. This risk is very small, given that the antibiotic residues in meat are very carefully regulated and treated animals can only be slaughtered after the specific time needed for residues to be eliminated has passed.
A more significant problem than residues is the direct passage of resistant bacteria to people. It is inevitable that an animal treated with antibiotics will develop some resistant bacteria that can then be transferred to humans through contact with animal feces. Farmworkers can become infected and then spread disease. Meat can also become contaminated during slaughter, and traces of fecal matter can be found on meat sold in stores. While heat can kill most bacterial contaminants, inadequate cooking or improper handling before cooking can contaminate surfaces and possibly other foods that are not cooked. Of course, we do not want to consume meat from sick animals either, so blanket elimination of antibiotics is hardly the answer. Emphasis has to be on the proper and judicious use of these life-saving drugs.
What constitutes an improper use? Feeding antibiotics to animals to make them gain weight more quickly would be one. Although penicillin was discovered by Alexander Fleming in 1928, it was not until the 1940s that it came into widespread use thanks to the work of doctors Howard Walter Florey and Ernst Boris Chain, who managed to isolate the drug from the penicillium mold and developed methods for producing it on a large scale. This 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 novel drug, they noted that it caused animals to gain weight. That finding was quickly spun into a commercial enterprise, namely selling antibiotics to farmers who were keen on increased profits by bringing their animals to maturity more quickly. The concept of resistance to antibiotics was not even on the horizon at the time and the addition of antibiotics to animal feed became a widespread practice.
By the early 21st century, the problem of resistant bacteria fostered by the use of antibiotics both 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 both Canada and the U.S followed suit. With companies no longer able to sell antibiotics to farmers as growth enhancers, they switched to promoting low-dose antibiotics in feed as a way of preventing disease. As a result, there was no significant reduction in the exposure of the animals to antibiotics. Growing concern over bacterial resistance as well as consumer resistance to purchase meat that may contain antibiotic residues has now steered farmers away from the prophylactic use of antibiotics.
Altered practices can also reduce the need for such prophylaxis. For example, piglets naturally wean around 3-4 months of age, but on “factory farms” they are often weaned after a month. In this case, they haven’t had enough access to antibodies from the mothers’ milk making them more prone to gastrointestinal disease 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 disturbed microbiome can lead to later disease requiring antibiotics. Poultry microbiome is also affected by intense farming practices. Chicks absorb microorganisms through the pores of the egg during brooding but in modern farming, the eggs are taken away from the mother and are cleaned on the surface. Furthermore, once the chicks hatch they do not have the opportunity to go outside and peck away at soil with all sorts of bacteria that would diversify their microbiome and prevent disease. So again, farmers look to prophylactic antibiotics for help. Too bad.
While antibiotic residues in meat are unlikely to have an impact on human health, generating antibiotic-resistant bacteria in animals does pose a threat to people. That’s why meat labelled “no antibiotics ever” is enjoying increased sales despite higher cost. However, it must be pointed out that the improper use of antibiotics in humans presents a far greater risk than their use in animals. Pushing doctors to prescribe antibiotics when they are not indicated is tantamount to crying wolf. Should a wolf really come to the door, cries will then bring no help.
Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.