A recent study from the Maryland School of Public Health has found a simple way to help overcome the health problems caused by antibiotic resistance: stop adding antibiotics to animal feed. The study found that when poultry and beef are produced without these antibiotics, bacterial resistance quickly declines.
Feeding antibiotics to livestock creates an ever-increasing number of antibiotic-resistant bacteria, including many that cause disease in humans. Yet up to now, no one has been able to say how quickly the damage can be undone by ending this practice or if it can be undone at all.
The Union of Concerned scientists estimated that 70% of all antibiotics in the U.S. (24.6 million pounds annually) are fed to healthy livestock, not taken by people.
The study, by a team that included researchers from Pennsylvania State University and Johns Hopkins Bloomberg School of Public Health as well as the Maryland School of Public Health, found an immediate and substantial decrease in antibiotic-resistant bacteria on poultry farms that had just switched from conventional to organic practices. And this happened in the very first flock raised organically.
But this study's findings won't become reality on their own. Meat and poultry farmers must embrace it. For that to happen, consumers will have to persuade them through the power of the pocketbook.
Including antibiotics in animal feed became routine soon after the rise of feedlots. Meat animals are fed antibiotics because doing so increases their weight and makes meat production cheaper. As far back as 1946, it was known that healthy animals fed low doses of antibiotics – doses strong enough to kill some of the animals' internal bacteria but not all of them – grew to market weight on less feed than animals that weren't fed antibiotics.
"You start giving [cattle] antibiotics, because as soon as you give them corn, you've disturbed their digestion, and they're apt to get sick, so you then have to give them drugs, says Michael Pollan, author of In Defense of Food: An Eater's Manifesto. "That's how you get in this whole cycle of drugs and meat... Once they start eating the [corn], they're more vulnerable. They're stressed, so they're more vulnerable to all the different diseases cows get."
Because of this, meat animals are also fed antibiotics protectively, to prevent the spread of disease before disease even occurs. Meat animals are raised under highly crowded conditions, which means that on the typical meat or poultry farm, one sick animal can easily infect all the others. This is similar to what occurs with people living in overcrowded conditions, where disease rates traditionally soar.
When antibiotics are fed to farm animals, even at the low levels used to aid growth, the remaining bacteria within the animals tend to acquire resistance to them. This was seen as early as 1951 in streptomycin-fed turkeys. But it didn't set off many alarm bells. The main impact of antibiotic resistance is seen in infections in humans, but back in the 1950s an infection that couldn't be cured with streptomycin could still be cured by using penicillin or some other antibiotic. But that was about to change.
Bacteria spread antibiotic resistance to other bacteria, even bacteria of a different species, by genetic transfer. This means that a harmless intestinal bacterium could make a disease-causing bacterium antibiotic resistant. Sewers are excellent breeding grounds for such transfer. This began to set off the alarm bells. But it wasn't until the advent of methicillin-resistant Staphylococcus aureus – MRSA – that the alarm bells really began ringing.
Antibiotic resistance was no longer a theoretical topic for scientists to discuss. It was now an extremely serious health problem.
A 2007 study published by the CDC found that 20% of all human MRSA in the Netherlands is of animal origin, from pigs and likely from cows. And the researchers strongly doubt that this problem is confined to the Netherlands. In other words, antibiotic-resistant bacteria from farm animals have been linked to antibiotic-resistant infections in humans.
The issue of whether antibiotic-resistant bacteria from farm animals have already caused infections in humans is really moot. The ease with which resistance spreads from one species of bacteria to another means that the pool of drug-resistant bacteria created on animal farms is bound to spread to humans sooner or later. Unless of course, these resistant bacteria can be reduced or eliminated.
This was the idea behind the Maryland School of Public Health study. Could drug-resistant bacteria be discouraged by a reduced reliance on antibiotics?
Bacteria don't choose to become antibiotic resistant. When they are growing in the presence of an antibiotic that would normally kill them, those that are able to resist the antibiotic survive and breed, while those that don't die. It's a survival trait, pure and simple.
When antibiotics are removed from feed and no antibiotic is present, the energy spent on antibiotic resistance is no longer a survival trait, it's a liability.
But what happens when that antibiotic disappears? Antibiotic resistance, whether caused by a protein that inactivates the antibiotic or a pump that transports it out of the cell, comes at an energy cost to the bacteria.
When antibiotics are removed from feed and no antibiotic is present, the energy spent on antibiotic resistance is no longer a survival trait, it's a liability. Non-resistant bacteria now are more energy efficient and should be at an evolutionary advantage and grow better, eventually replacing their resistant cousins. At least that's the theory. The Maryland researchers decided to put this theory to the test.
They looked at the resistance of two species of Enterococcus, Streptococcus-like bacteria found in the intestine and colon of both poultry and humans. These bacteria normally cause no harm but can cause infection when they spread to other parts of the body. Because Enterococcus species are a major source of hospital-acquired infections in humans and because they can spread resistance to other bacterial species through genetic transfer, they're medically important bacteria.
Resistance to the vast majority of antibiotics tested was lower on the newly organic farms. For example, 81% of the E.faecium on conventional farms were resistant to tetracycline, compared to only 12% on the newly organic farms.
The researchers collected bacterial samples from poultry litter, feed and water and tested their resistance to 14 antibiotics. They looked at the two most common species of Enterococcus, E. faecalis and E. faecium. These bacteria spread from farm animals, chiefly through animal waste, into air, soil and water.
Resistance to the vast majority of antibiotics tested was lower on the newly organic farms. For example, 81% of the E.faecium on conventional farms were resistant to tetracycline, compared to only 12% on the newly organic farms. And while all the declines seen weren't this spectacular, the researchers emphasize that all this occurred in the very first flock grown organically. The decreases are only expected to grow larger in the next year or two.
The results of the study are summarized in the table below.
|Number of:||Organic Farm||Conventional Farm|
|Antibiotics with Fewer Resistant Bacteria||11||0|
|Antibiotics with Zero Resistant Bacteria||5||3|
|Multi-Drug Resistant Bacteria||17%||84%|
|Antibiotics with Fewer Resistant Bacteria||9||1|
|Antibiotics with Zero Resistant Bacteria||5||2|
|Multi-Drug Resistant Bacteria||10%||42%|
There are likely still sources of residual antibiotic-resistant bacteria remaining on the newly organic farms, even after the extensive cleaning required to be certified as organic. These should diminish over time and lead to even lower rates of resistance. And even organically-grown poultry can still have major exposure to antibiotics. They can't be fed antibiotics, but this prohibition only applies from the first day of life onward. Breeder facilities and hatcheries are allowed to inject antibiotics into eggs and the chicks that hatch are still certified organic.
Other countries have already acted to curb antibiotic feeding to livestock. Most notably, the European Union banned feeding of all medically important antibiotics to livestock in 1998 and followed that with a total ban on all antibiotics in 2006.
There haven't been many studies done on the effect of banning antibiotics in livestock in Europe and Asia. Two that have been done firmly support the Maryland study's results.
The European Union banned feeding of all medically important antibiotics to livestock in 1998 and followed that with a total ban on all antibiotics in 2006.
Taiwan banned the use of Avoparcin as a feed additive in 2000. Avoparcin is an analogue of the antibiotic vancomycin; bacteria that are resistant to one of these antibiotics will almost always be resistant to the other. Testing the same two bacterial species that were tested in the Maryland study, a 2007 study found that vancomycin resistant enterococci on chicken farms decreased nearly fourfold from 2000 to 2003, dropping from 13.7% to 3.7% and 3.4% in the two Enterococcus species.
A 2001 study from Denmark tested the effect of the 1998 ban on medically important antibiotics. It compared the antibiotic resistance of E. faecium from broilers in 2000 to the pre-ban level in 1997. It found that resistance to four medically important antibiotics — avilamycin, avoparcin, erythromycin and virginiamycin had each dropped greatly, to between one half to one-fourteenth of their 1997 level by the year 2000.
Both these studies offer the same lesson as the Maryland one: Stop feeding antibiotics to livestock and antibiotic-resistance in bacteria will quickly decline.
People have been given a vision of a future where antibiotic resistance begins to fade, instead of becoming a more serious medical problem with every passing year. But expecting industry to take the lead ignores the lessons of the past. Historically, businesses have been loath to change lucrative practices for the sake of the social good without some type of pressure that forces them to do so. That leaves it up to consumers to make this vision real.
Americans have said no to the food industry before: they rejected New Coke simply because they didn't like the taste, and the Coca-Cola company ultimately had no choice but to bow to their wishes.
There's no question that if enough people reject antibiotic-fed meat and poultry, the industry will have to change their practices. But organic meat and poultry do cost more. And some people simply can't afford to pay much more. Buying at farmers markets or directly from the farmer can help, since prices will be lower. And as the organic market share grows, prices should also begin to drop.
For those who can afford the price, the question becomes simpler: what kind of world do you want to live in? If you'd like one where antibiotics can still cure infections, it might be time to start buying organic meat and poultry. And there could be a bonus: many people say that organic meat tastes much better.