If I were to define myself professionally, I’d say I am equal parts microbiologist, molecular biologist, and biochemist. I obtained my doctorate in biochemistry in 1986, working on the genetic instability and antibiotic resistance of bacteria. Since then, I’ve studied bacterial pathogenesis, vaccine biotechnology, and more recently, the biochemistry of iron uptake by Escherichia coli and Listeria monocytogenes, two potentially lethal bacterial contaminants of food. As a result of these experiences, I have strong opinions about the use of antibiotics in food production.
Watching the news this week, I saw a pig farmer from my home state (Oklahoma) defending the practice of feeding pigs antibiotics to improve their health and weight. I’d love nothing better than to invite that man over for a cup of coffee and a conversation, so I could ask him what exactly he knows about the use of antibiotics. For example, has he ever heard of the term “plasmid?” What about you? If you care to read about it, then follow me to the next page….
Bacteria possess efficient and sophisticated responses that block antibiotic action, which existed long before we “discovered” them (in 1929), before we learned to produce them (in 1943), and before we created new, more potent derivatives, sometimes with a broader spectrum of microbial targets. Just like any living organism, bacteria organize their DNA in a chromosome, usually a single, large molecule that contains all the genes for survival and replication (in E.coli, that’s almost 4,500 genes). But, bacteria often possess additional DNA, much smaller and not part of the chromosome: this DNA is in the form of plasmids.
Keep in mind that the cartoon is not to scale: the chromosome is huge, and very tightly packed. Plasmids are a few thousand times smaller, but they may be present in high numbers, as much as hundreds of copies per cell. Plasmids usually contain genes that are not needed in “normal” situations, but are useful in adverse situations. Indeed, in the 1960’s scientists found that the genes that confer antibiotic resistance are often located on plasmids. This fact gives the microbes an added bonus, because plasmids may be transferred from one bacterium to another. A conjugative plasmid sends a copy of itself to other bacteria, in a very cool mating process. Yes, even these tiny unicellular creatures are into sexual activities, if the conditions are just right for it… 😉
Since the first antibiotic – penicillin – was discovered (in a very fortuitous way by Fleming), we’ve witnessed incessant evolution in the microbiological world: every new weapon designed by humans to eliminate bacteria is soon followed by the development of drug resistance, and as new resistance genes arise, they often associate together to form larger and larger plasmids, containing multiple drug resistance genes. You can read about a carefully studied example by clicking here.
At first, scientists were a bit puzzled by resistance genes ending up all neatly organized in plasmids, but later it became clear that these genes efficiently move among bacterial populations, literally “jumping around” from one place to another. They are classified as “transposons“, which gives an intuitive idea of what they do: they transpose themselves to new locations, while leaving the original copy of the antibiotic resistance gene in place.
Back to food. When farmers treat animals (like pigs) with antibiotics to produce more meat and “healthier” animals, they create strong selective pressure on the bacteria in the pig stomachs and on their skins, so that rare, antibiotic-resistant variants will arise, survive and take over the population. It’s only a matter of time. Many of these bacteria are potentially pathogenic in humans, and they will have plasmids that can be transmitted to other bacteria, including bacteria in the human digestive tract. So, even if the bacteria are themselves non-pathogenic, they may pass their antibiotic resistance to more harmful microbes by conjugation or other processes. Besides that, the antibiotics are eliminated in the animals waste, and end up permeating the soil, ultimately draining into rivers, lakes and reservoirs used for drinking water and irrigation of food crops in the surrounding regions. So the selective pressure for antibiotic resistance becomes ubiquitous, leading to the development of more and more dangerous bacterial strains.
Here’s some good news: the selective pressure works both ways. Carrying the extra DNA associated with plasmids is a heavy metabolic load for the bacterial cell. If you stop adding antibiotics to animal food, plasmid-free bacteria will have an advantage in growth and replication, and soon take over the population. The upshot of these explanations is clear: the less antibiotics that we use, in food production and in medicine, the better it is for the future of mankind.
Antibiotics as a preemptive measure in food production are unnecessary and driven by obsession with profit. This practice, that has undeniably caused infections in humans with microorganisms that are completely resistant to multiple drugs (click here for a very good article) was already banned in many European countries. Here in the US we witness a huge opposition to responsible action in the right direction. Why? In part because drug companies do not want to lose their profits from drug sales to the food industry. And in part because large-scale farming walks hand in hand with the pharmaceutical industry, hoping to raise their own profits by making meat artificially cheap, so that we eat lots and lots of it, even knowing that the practice is unhealthy. Ironically, if farmers stopped excessive antibiotic use, the price of pork would only increase by a meager 20 cents per pound. Twenty – cents – per – pound. Does that 20 cents a pound justify the threat of infections by antibiotic resistant bacteria?
Michael Pollan wrote two masterpieces on the subject of the American food industry. I highly recommend that if you haven’t read these books, do so as soon as possible. The bottom line is that by producing our food as cheaply as we possibly can, we are affecting the balance of our planet. We are raising cattle, pigs and chickens in horribly crowded conditions so that we can buy cheap meat, chickens for $3 per pound and eggs less than $3 per dozen. I do not advocate turning into vegetarians: my motto has always been “everything in moderation“. But, at some point, we need to stand up for what is right.
The practice of using antibiotics on healthy animals is irresponsible. Don’t let anyone fool you.
Bewitching Kitchen 
Really interesting post! Is it that many Americans aren’t aware of this yet? Just wondering, because here in Germany it has been debated for quite some time already.
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It’s been in the news quite a bit lately – one of the problems is that last year they tried to pass legislation about it, and it was blocked by Congress in November, if I remember correctly. But somehow not too much “noise” happened then – now, a few months later, we see the issue brought to light again.
Here, depending on the state people might or not be fully aware of it – California, as usual, is way ahead of states like Oklahoma in this regard.
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Thanks so much for this great article. I too, come from a micro/nutrition background with the added interest of a year of post-graduate animal science. Loved your article. This is why I’m becoming so much more interested in raising my own food.
I see you’re in Oklahoma. I went to Med school there and and was stationed there for 7 years. Want to move back there soon and start my little farm!
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Sally, você colocou uma explicacao cientifica e racional no que pra mim era apenas senso comum. obrigada! e beijos,
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Fer, que bom que voce gostou! O assunto e’ algo que me incomoda muito, principalmente por morar em um lugar em que o que deveria ser “common sense” , nem sempre esta’ presente.
Fiquei pensando se deveria ou nao escrever a respeito, mas…. I’m glad I did 🙂
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great post, I like how you broke this down to be easily understood. We will be moving back to he US this summer and hope we will find a good source to get chicken, eggs and meat that are raised the right way. Here in Bavaria/Germany it’s so easy and I getmy chicken and eggs from a farm right in town. El Paso Texas I am sure will be another story.
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Petra, we will be quite a bit closer once you move to El Paso! Good luck with your move, these intercontinental moves can be pretty painful sometimes… 🙂
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Nicely explained, Sally. I’m going to refer this to my friends and relatives.
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Thanks, Jean! I really appreciate it!
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Great blog and interesting post. We really need to bring this problem of excessive and unwarranted antibiotic use in food production to people’s attention. You are absolutely right about major motives. Drug companies sell more antibiotics to food industries than to clinics.
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For those who don’t know, Dr. Zgurskaya is a renowned researcher and expert on antibiotic resistance in bacteria.
Thanks for your affirmation!
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Sally, this is an issue I’ve been concerned about for a long time. My understanding is that there is more antibiotic resistance from animal products in our diets than from human antibiotic consumption. Since antibiotics are notoriously overused in humans, this is shocking. Something certainly needs to be done, but it will be a long road ahead.
Great post…thanks for helping to increase awareness.
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Nicely written, Sally!
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@ Marcia & Steven: Thank you!
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I wish everyone who buys cheap meat would read this Sally. I’ve linked to it in Twitter.
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Thank you, Barbara! If this post helps clarifying the issue, I am more than happy!
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Hi Sally, with your professional hat on, very interesting! I have always said that one of the benefits of organic food is not so much what is put in it, but what is left out, i.e. the routine and unnecessary antibiotics. I am not a scientist but do find epidemology very interesting from a sociologicial perspective, so try hard to understand the science! As a side note to this, do you have any view on the use of aged eggwhites to make french macarons? This is basically leaving eggwhites sitting around at room temperature exposed to the environment in order to ‘age’ them. I think so that they become less watery? It doesn’t sound particularly safe to me, I wonder if there is a scientific perspective on this…
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Hi, Zeb…
A few things to consider – these numbers are not set in stone, but the proportion of contaminated eggs in the USA is at most 1 in 10 thousand, probably more like 1 in 30 thousand eggs. So, you would have to be quite unlucky to get a contaminated egg for your macarons.
That leaves the possibility of contaminating them from the outside by leaving the egg whites exposed to the environment. Well, under normal conditions, there will be no pathogenic bacteria lying around your home, and egg whites do have a series of substances in them that make it very hard for many species of bacteria to grow (lysozyme, avidin, apotransferrin).
So, interestingly enough, the practice of aging egg whites is not as dangerous as it may sound. When you add to it the fact that you will ultimately cook the egg whites during baking, all should have a happy ending.
Now, keep in mind that certain conditions might make a person more susceptible to infections – immunocompromised individuals, elderly people, pregnant women, babies – so just to be on the safe side, I would not do this if cooking for them.
Feel free to drop me an email if you want more specifics…
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Hi Sally, thanks for the reply. It sounds as if American eggs have a lower incidence of salmonella than Euro eggs! Last survey that I can find for the UK says 1 in 2000 eggs. Very interesting to hear about the substances that egg whites have in them to inhibt bacterial growth, I was always under the impression that eggs were used to grow things like viruses and so on for vaccines, so thought they would be more susceptible rather than less, but not being a scientist just shows my level of general ignorance 🙂 Anyway this is off topic I guess and I am not rushing to make the macarons, looks very fiddly! Take care Zeb
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Actually, when you use the eggs to grow viruses for vaccines, the inoculation is straight into the yolk, that doesn’t have the same substances the egg whites do. Also, viruses would not be susceptible to them.
Interesting that the level of contamination is so much higher in the UK – now I am a little suspicious of the statistics found here :0)
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Not only does the promicuous use of antibiotics in factory farming select for resistant bacteria, it sends microbes the wrong signal: I wrote an article on the small molecules we call antibiotics in the American Society for Microbiology’s Microbe magazine (October 29th –I think– 2009). In their usual doses in soil, antibiotics are used for lots of things including signaling other microbes to form biofilms –where we can’t get them. We need to stop using anti-infectives as a substitute for good farming; it doesn’t work anyway.
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