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roundtable: the evolving enemy Watch Show 4:
"The Evolutionary Arms Race"
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How concerned should we be about becoming infected with resistant bacteria from foods like chicken, beef, and even aqua-cultured fish that may have been grown on diets treated with antibiotics? Will eating less of these foods, perhaps by switching to "organic" chicken, reduce our risk, and do vegetarians have a reduced risk for this reason?
If the use of antibiotics in a widespread fashion at low doses in agriculture, particularly in the raising of animals, is so common and yet so potentially dangerous from the standpoint of evolution of resistance, why is it still the practice? What are the costs and benefits of this practice?
Several people have submitted questions not about antibiotics, but about all of the liquid soaps that are now for sale in supermarkets that are labeled "antibacterial." Do these work like antibiotics in causing further resistance? If so, how, and if not, how is their action on bacteria different than just plain soap?
Americans now seem to be getting fanatic about sterility, and people are trying to raise their children in an almost "germ-free" environment. We have a question from a woman who says that she has several friends, young mothers, generally, who seem to overuse antibacterial products. She asks: Is it not true that the presence of some "germs" in moderation is actually good for the development of our immune system?
In one of the programs in the Evolution broadcast series, there was the story of the leafcutter ants that culture Streptomyces bacteria on their bodies and seem to use those bacteria to apply antibiotics to keep their fungal farms parasite free. This has been inferred to mean that somehow the Streptomyces and the antibiotics they produce have been evolving with the enemy, and this is a kind of use that appears to have been going on for 15 million years without permanent resistance being developed. Is there anything we can do to put ourselves in that situation versus the more static situation we're in now?
Could you give an explicit description of how evolutionary theory informs integrated pest management? I think the cross-fertilization here between bacteria and antibiotic resistance and agricultural pests and insecticide resistance is very interesting, and I don't think many people make that connection.
Some physicians, who are quite impassioned, say they would like to prescribe fewer antibiotics, but their patients demand them. Since in effect they cannot be absolutely positive there isn't a bacterium involved, when, say, a parent brings in a young child who is ill, and they can't be absolutely certain that there won't be bacterial complications as a result of a viral illness, they would like to know how the public will be educated and who is going to take on the job, so that patients will basically get off the doctors' backs and let their colds run their course.
Another part of that question is that doctors are afraid of being sued if they don't prescribe an antibiotic and a bacterial infection does develop. So from the medical perspective of overuse of antibiotics, how might we address this basic problem in the interface between healthcare providers and the consuming public?
   

 

Q: How concerned should we be about becoming infected with resistant bacteria from foods like chicken, beef, and even aqua-cultured fish that may have been grown on diets treated with antibiotics? Will eating less of these foods, perhaps by switching to "organic" chicken, reduce our risk, and do vegetarians have a reduced risk for this reason?
Panelist Responses: < back to intro page
Stuart Levy
I'll take the first question, since it seems to be in my area. I would say that the answer is yes, there is a risk. In fact, until the farm community and the food industry can assure [people] that resistant bacteria are not associated with meat and food products, everyone should take the advice of the Department of Agriculture and Food and Drug Administration, and that is to prepare your meats on separate counters from your salads and other items that won't be cooked. When you cook your meat, you will destroy the bacteria that are on it. In the United States, these bacteria are generally harmless, but in chicken and some other meats you can pick up bacteria that are toxic, such as salmonella or a toxic form of a common bacterium that we all carry called E. coli.

The fish industry is much less risky in the sense that there are tremendous new efforts to reduce antibiotic use. The reason I mention that is the presence of resistant bacteria is linked to the use of large amounts of antibiotics in the raising of food stock. This has changed considerably in the raising of fish, and there have been huge reductions in the amount of antibiotics used, although there still will be and have been reports of bacteria with resistance associated with fish. I would say that for the time being it doesn't hurt to prepare any foods that are coming from outside, fish or meat, on a counter that's separate from your uncooked salads and other vegetables.
George Beran
We do have an increasing level of safety in our fresh meats, and that includes poultry and beef and pork. That doesn't mean that they are totally safe. It means that this is a major target in our whole food safety system -- in the slaughter and processing. The levels of bacterial contamination are going down, but that doesn't mean that we don't occasionally find salmonella and another kind of bacteria called Campylobacter, which is very common in poultry and in cattle, though it less commonly contaminates the beef than it does the poultry. And we certainly are working to bring those levels down further. What you say about making sure that your kitchen is clean, that you're not using the same cutting board for cutting up chicken or other meat as you then use to cut up foods that will not be cooked, is good advice.

Switching to organic meats will make no difference, nor do vegetarians have a reduced risk. These bacteria that we are talking about are very, very common, and they do contaminate food both in organic production and in conventional production. We don't know whether there's a real difference here between the level of occurrence of this contamination in organic production, in conventional production, and in vegetarian, because these bacteria are on the foods that we eat in a vegetarian diet, too. So the answer is that as of the present time, there are bacteria and they have similar levels of resistance in all of these types of food. The organic producers are paying very close attention to this, and we may see some changes in the future.
Tamar Barlam
I think that a lot of the advice that has been given is just generally good advice in terms of food preparation and doesn't necessarily speak to the special issue of resistance. I think that if you do have a lapse in your food preparation or if you're exposed to food that hasn't been prepared in a proper way, then the use of antibiotics in food animals, in agriculture, certainly does make it more likely that the bacteria that you encounter will be resistant to a treatment that you might receive. And this is one reason, for example, that the Food and Drug Administration has proposed banning one of these uses in poultry -- because of concerns that if you do get an infection with Campylobacter, you might be more likely to have a resistant bacteria because of antibiotic use.

So I think the general advice given -- clean your vegetables, etc. -- is good for all meal preparation, organic or non-organic, but I think that the special issue of antibiotic use in food production is that the bacteria would be more likely to be resistant, and that would potentially increase the health risk to the person.
Stephen Palumbi
The interesting comments earlier seemed to say, if I can paraphrase and then ask you whether that's what you really meant, that you're just as likely to pick up a resistant salmonella off a carrot as off of a piece of chicken. Is that really so? Are there studies that show the level of resistance in bacteria is just as high on vegetables as they are on meat products?
George Beran
You're not that likely to pick up salmonella off of the carrots. Our carrots come packaged, and the usual situation now is that they are cleaned before packaging. You're much more likely to pick up food-borne bacteria -- and it's much more likely that they would be resistant -- on meat and meat products than you are on vegetables. But the presence is there throughout the environment.
Stuart Levy
I think that's the critical point. Whenever you give an antibiotic, whether it's to people or to animals, the antibiotic doesn't just get broken down immediately; it enters the environment in one way or the other. Either it goes into sewage systems, or, in the case of animals, generally the manure is plowed into the fields or put in other places. If it's in the water, it often goes out into the general environment.

So you have, in fact, an environmental effect, an ecological effect of antibiotics, which far exceeds, in its impact on resistance, that which occurs in the people or animals that are being treated. Antibiotic use really pushes the evolutionary process to favor organisms that are resistant. Any individuals in the bacterial population that is being targeted that happen to have genes that give them resistance to the antibiotic will survive and multiply. And because bacteria have the unique ability to transfer genes laterally -- to swap genes as though they were trading cards -- those resistance genes will be passed on to their neighbors and a kind of community resistance occurs. At the same time, this antibiotic resistance doesn't stay in the animals that are treated; it then goes back into the fields. We ourselves have studied fruits and vegetables and have found resistant bacteria.

The infectious types of bacteria have not been associated with food products, except in the case of the E. coli, which is toxic; that has been picked up in fruit juices. So I think that while there is concerted effort -- and I mean that -- to clean up the food products, there hasn't been, yet, a true advance in keeping out antibiotics when they are not needed. Echoing what Tamar was saying, I think there's a lot of use of antibiotics -- some estimate at least half, some would say greater than half of the antibiotics used in our United States for animals -- that are used not to treat diseases, but to help the animals grow.

Many countries in Europe have stopped doing this, have in fact banned the use of antibiotics to promote growth in livestock. And I think advances here in the United States would say that this use, which goes back to the '50s, is now outdated and can be removed without any real harm to the economy of this process or to people. In fact, there will be an advantage.
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