Carcinogens

[deleted-502772]

Hello,
I am a 9th grade student at Taunton High School, and I have chosen to do my science fair on the amount carcinogens in meat. I am currently searching for methods to use to detect carcinogens in meat. I was wondering if someone would be able to give me some advice or help me throughout my science fair project. It would be greatly appreciated, thank you.
Sincerely,
Olivia Weber

[deleted-291782]

Hi Olivia,

I'm not entirely sure that I can help you much and hopefully another expert can weigh in with their opinions. Your project sounds like it will be very heavy in organic chemistry, and you will likely need to use some common chemistry lab techniques to be able to detect the carcinogens in the samples. What stage of the project are you in currently? What are some of your main questions? Let us know and we will be happy to help.

Best,
Pharma

[deleted-502772]

Hi Pharma,
Some of my main questions right now are, how exactly does the procedure go for the ames test, and how will I test the actual meat for the carcinogens. I am currently at the stage where I must find three articles regarding the topic to show to my teacher, after this we will begin our introduction. Today, my teacher approved my topic and the ames test, as long as I find the procedure.
Thank you,
Olivia

[SciB]

Hi Olivia,

You have picked an excellent question to ask and hopefully we can help you do a project to get an answer.

The Ames test was developed almost fifty years ago as a way to identify mutagenic (and therefore potentially carcinogenic) substances using the bacterium Salmonella typhimurium. The principle is pretty simple. The bacterium itself has a mutation in its DNA that makes it unable to synthesize an essential amino acid, histidine. In the lab you can grow the bacteria on a Petri dish if you include histidine in the agar to supply what they are unable to synthesize. To do the Ames test you expose the bacteria to a substance that you suspect may be mutagenic and then spread them on agar containing a little histidine. The idea is that a chemical mutagen will cause a back-mutation in the gene for histidine biosynthesis so that the bacteria are again able to synthesize the amino acid. These bacteria will grow normally on the agar because they do not need histidine and therefore will make large colonies that you can count. You compare the bacteria exposed to the test chemical with bacteria exposed to sterile saline and if the test bacteria show significantly more colonies on the Petri dish than the controls you can conclude that the chemical is a mutagen and may be a carcinogen. Remember that not all mutagens are carcinogenic but there is a fairly good correlation, enough to warrant additional testing using animals or human cells in culture.

Now, after that rather long explanation I have to tell you that Salmonella is a human pathogen and you would not be allowed to use it in a science fair project (https://www.msdsonline.com/resources/ms ... typhi.aspx)

However--you should be able to use the nonpathogenic variant of the bacterium Escherichia coli (E. coli) known as K12 provided your school has a basic microbiology lab that you can work in or will allow you to do experiments with it at home. The only problem I foresee is obtaining a K12 strain of E. coli that has a mutation in one of its metabolic pathways that causes it to be unable to synthesize an amino acid, usually tryptophan in the case of this bacterium. If you can find such a bacterium then you can use it to do the Ames test just the same way as you would using Salmonella.

Carolina Biologicals (https://www.carolina.com/browse/product ... ubmit=true) sells the E. coli K12 strain and if you call them and ask to talk to technical support and tell them what you want to do, they may be able to help you. There is another E. coli strain called WP2 that has a mutation in tryptophan biosynthesis and this bacterium has been used for the Ames test also (Mortelmans K, Riccio ES. The bacterial tryptophan reverse mutation assay with Escherichia coli WP2. Mutat Res. 2000 Nov 20;455(1-2):61-9. Review. PMID: 11113467 ) but I don't know if it is a derivative of K12 and non-pathogenic.

If there is a university near where you live that has a microbiology department, you could talk to someone there and tell them what you want to do and ask them for help. Someone should be able to tell you if WP2 is safe to use and where you can get it.

I hope this is not too much information! You probably have lots of questions so please post again if you still want to continue with this project and we will try to make it happen. Working with bacteria is quite simple and there are a number of good videos on Youtube as well as information on Scibuddies (https://www.sciencebuddies.org/search?v ... h+bacteria) that you can use to learn the techniques, but first you need the permission to use the organism to test the potential carcinogenic substances.

Let us know how you make out.

Good luck!

Sybee

[deleted-502772]

Hello!
Thank you so much for this explanation. I have talked to my teacher and she approved this as long as I use E coli. I am also in touch with the head of science in my school. I have decided to test the different amounts of carcinogens in chicken cooked with charcol vs gas vs in the oven vs on the stove. I have a few questions though. When will the chicken come into play in the procedure?
Thank you,
Olivia

[SciB]

Hi Olivia,

Glad to hear that you have been approved to do the carcinogen project--provided you can get the necessary E. coli strain and have a place to perform the experiments. Will you be able to do the work in a lab?

Can you please state your hypothesis? You gave several variables--charcoal vs gas for cooking and oven vs stove--but did not say why you chose those or what question you are asking. Having too many variables in one experiment makes it harder to perform successfully and interpretation of the data more difficult. I suggest that you choose only one independent variable at a time--either the source of heat or how it is applied.

Now, to answer your question about when you test the chicken mutagen. I don't know how familiar you are with the method but the key part of the Ames test is exposure of the bacteria to the substance that you suspect is mutagenic. Notice that I said 'substance'--not chicken. In the Ames test, the bacteria are grown in what is called a liquid culture in a sterile broth and then spread onto agar in a Petri dish to test whether they have back-mutated. The bacteria are exposed to the test substance while in the liquid culture and then they are collected by centrifugation, rinsed to remove the chemical and resuspended in sterile saline. A drop of the suspended bacteria is put onto the agar and spread over the surface. The plate is then put into an incubator for a day or two so the bacteria can grow if they have mutated.

Do you see the problem? Charcoal grilling chicken may produce mutagenic substances but you cannot add a piece of chicken to the broth containing the E. coli bacteria. A biochemist who wanted to perform such a test would first make an extract from the chicken and that would be the substance that was tested. It is possible to do this but I am not familiar with the method. You need to read more about how the research was done some years ago that showed carcinogenic substances were produced in meat that was charcoal grilled.

One important thing to keep in mind is that what you are actually doing in the Ames test is counting bacterial colonies on agar in a Petri dish. So, if you add something to the bacterial culture that is not sterile--that has other bacteria or fungi in it--these may grow on the plate and ruin your experiment. The chicken extract that you expose the E. coli to has to be sterile. There are several ways you could sterilize the extract but it will depend on how the extract is made so you will have to find out how to do that first.

I know this may sound like a lot of work and it is, but it is a really great project if you can accomplish it successfully. Scientists have to struggle with loads of details just like this every day, and one mistake can mess up an entire set of experiments.

Please get back to us when you have decided what your hypothesis is and how you want to do the experiments and we will try to guide you through the project. Hopefully you will be able to work in a good lab with someone who knows how to grow and plate bacteria and can help you with the methods. They are not difficult but you need to watch someone do them and ask questions before you try it.

Good luck!

Sybee