Antibiotic Resistance in Cow Manure

Antibiotic Resistant Genes

external image GP2144.jpgexternal image cowstomach.gifRecent studies in biochemistry have shown that some bacteria inside cows' stomachs are becoming immune to antibiotics. Cow manure, commonly used as fertilizer, could possibly help in transferring these bacteria to soil where food is grown for humans to eat. Most
of these bacteria don't pose a threat to our safety at the moment, but it is possible that these resistant genes could appear in harmful bacteria, causing food-borne illnesses or hospital infections.

Researchers from Yale investigated whether the use of cow manure as a fertilizer would create a conducive environment for these AR (antibiotic resistant) genes moving into the human ecosystem. What these researchers found is that there were 80 AR genes in only five samples of manure. When these AR genes were added to strains of E. coli, the E. coli became resistant to β(beta)-Lactam (think penicillin) and three other kinds of antibiotics.

How Could these Genes Affect Humans?

There are two ways that AR genes can come in contact with humans.The bacteria with these genes could colonize humans, which has appeared in farmers who receive bacteria from their animals. The other method in which AR genes go from animals to humans is through a process called "horizontal gene transfer" where some genes are able to "jump" to unrelated micro-organisms. What this means is that some bacterium with AR genes that is harmless to humans could transfer the AR genes to pathogens.

Another way that this is dangerous to humans is that in response to these bacteria becoming immune to many basic antibiotics, big companies want to start using more powerful antibiotics, like cefquinome, to get rid of the bacteria. If the bacteria become resistant, they could be spread to people that eat under cooked beef, dairy products, or any food products that are grown with the help of cow manure for that matter. Antibiotic resistance is no joke. In the past decade, the number of bacteria that are resistant to antibiotics has skyrocketed in the past decade. If not put in check, we could have a serious problem on our hands.


Kyle R.- Could you please delineate what is meant when you say that AR genes may colonize humans? Does this merely mean that AR genes could grow on humans?

David K. - How could the spread of AR genes to dangerous bacteria be prevented? Are governments taking any measures to try and prevent this?
  • Nicholas T. Antibiotics can kill the bacteria, but not all of them. Bacteria that survive adapt and multiply to replace the killed bacteria. Their exposure to the antibiotics causes them to adapt and mutate to become AR. This new DNA code is easily transferable to other bacteria as well. Patients can take antibiotics exactly as the doctor prescribes and complete the course of treatment without skipping doses. This is to make sure all the bacteria is killed and there as no survivors to mutate resistances. Another way is to reduce overall antibiotic use. Valuable drugs must be used carefully. Government intervention varies by country. Some allow antibiotics to be purchased OTC (over-the-counter). The World Health Organization has proposed a Global Strategy for Containment of Antimicrobial Resistance (warning: long, boring, do no read) that is aimed to help organize global action against antibiotic resistance

Anuj R.- So, it is agreed that antibiotics are meant to kill living pathogens, such as bacteria. The bacteria can mutate and survive antibiotics faster than we can make new, effective antibiotics. Is it possible for humans to mutate fast enough to survive the different harmful species of bacteria just as the bacteria mutate to survive our antibiotics? Explain. In other words, if they (the bacteria) can do it, why can't we do it (mutate and survive new harmful agents)?
  • Afroshark - We can't evolve as fast as bacteria do for two main reasons: They have shorter generation times, and and we help them to evolve even faster. About the first answer, a generation time is the time it takes to go from one generation to the next. For example, in humans, it takes on average about 20 years when someone has a kid for that kid to have a child. In bacteria, the average generation time is a few hours, and for some bacteria, only a few minutes. This allows adaptations in bacteria to spread much faster than it does in humans. We help bacteria to evolve faster by overusing and misusing antibiotics. Almost 50% of antibiotics prescribed to people in the US are unnecessary (i.e. for viral infections), and more than half of the antibiotics sold in the US go to cows and other livestock. Most of these cows have nothing wrong with them, but the antibiotics are given to them to induce faster growth. In addition, doctors often prescribe antibiotics that kill a wide spectrum of bacteria instead of running diagnostics to give the patient an antibiotic to kill the bacteria specific to them, or they give the patient the wrong antibiotics. Another problem is over-the-top medications that don't require a doctor's prescription, which leads to widespread misuse. The biggest problem is people not completing their prescriptions because they feel better before all of the antibiotics are used up. If all of the bacteria is not killed, then the remaining are left to reproduce and make more antibiotic resistant bacteria.

Blake M.- How do bacteria go about becoming antibiotic resistant in the first place? Yes, they mutate, but how does this mutation process start, and how quickly does this mutation process occur once it has began? Also, are there bacteria out there that have become completely immune to certain antibiotics, or can this mutation process only result in resistance.
  • Anuj R. - Well, Blake, that is quite the Honors Chemistry level question. One does not simply mutate during his or her lifespan. Mutations are caused by irregularities during the process of reproduction. So, to understand mutation, one must look at the cell itself, not the whole organism (if it is multicellular). We as humans have a very meticulous process of genetic material replication. As the bonds between the adenine and the thymine and those between the guanine and the cytosine are broken, enzymes, such as DNA polymerase, carefully produce two identical strands of DNA
  • .DNA_replication_split.svg.pngIn this image, the red circle indicates the area where the enzyme helicase is spliting the strand of DNA. The right split strand is the leading strand, which is continuously replicated by DNA polymerase III (don't ask me about one and two because my mind is already blown). The green arrow shows the direction of the DNA polymerase's movement. However, replication gets complicated (complicated also means well thought out and effective) with the left split strand, known as the lagging strand. Words cannot really do justice to the process of Okazaki fragments and RNA primase. This video will explain what I can't put into words:
  • Skip to 1:44; this is where the subject under consideration begins. So, as you can see, lots of care is taken during our DNA replication to reduce the probability of mutations. Remember, MUTATIONS ARE MISTAKES. ADAPTATIONS ARE HAPPY MISTAKES. Problems like Down syndrome are due to the incorrect separation of chromosomes during anaphase, but I digress. Also, we have societal values like laws and morality that prohibit blatant natural selection among humans.
  • On the other hand, bacteria don't have laws or a complex, meticulous DNA replication process. DNA in bacteria is oftentimes organized into a single, circular strand, called a plasmid. The splitting of the plasmid and completion of the divided strands is a much more simple, quick, and careless process in a bacterium.

Watch this; its informative. So, basically, there is a high possibility of error, and errors can happen more often because of bacteria's higher rate of reproduction. I'll let someone else discuss horizontal gene transfer. The mutation is a one time mistake during reproduction that stays with the organism. It is not a process that progresses. However, mutations can keep on occurring, reproduction after reproduction, to result in major evolution.

As for the second part of the question, the level of resistance is not exactly measurable, so it cannot be concluded that a bacteria is "immune" to an antibiotic. There might be some effect on the bacteria, but as long as the antibiotic does not kill the bacteria, the bacteria is resistant to that antibiotic. If I am not understanding what you think the difference is between immunity and resistance, please tell me. From what I have read, there isn't a specific category of immunity in bacteria as opposed to just resistance.