Test strips for E Coli and Salmonella

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Zebnd0281
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Test strips for E Coli and Salmonella

Post by Zebnd0281 »

What is the best method to test meat for harmful bacteria like e coli and salmonella? I am very interested to know how the test strips work and what chemicals or compounds are used in the test strips.
SciB
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Re: Test strips for E Coli and Salmonella

Post by SciB »

Hi and welcome to Scibuddies,

What test strips are you referring to? Can you explain more about these--maybe give us a link to a reference or website?

The tests I am aware of use antibodies against specific bacterial proteins to identify them but I'm sure there must be other methods. Give us some more information and we can try to answer your question.

Sybee
Zebnd0281
Posts: 5
Joined: Sun Oct 11, 2015 12:48 pm
Occupation: Parent

Re: Test strips for E Coli and Salmonella

Post by Zebnd0281 »

Thanks so much for the quick reply. Here are a few links to kits we have found online. Honestly we have found dozens online but they all seem to be rather similar.

http://ecolisalmonellatest.com/

http://www.nhdiag.com/ecoli.shtml

http://www.biooscientific.com/maxsignal ... p-test-kit

It appears that they are possibly using Kovacs reagent. We are just unsure of the steps to take and the process to create a project centered around creating test strips similar to these.

Also we have been pondering the usage of antibiotics residue found in meat. Is there such thing as a chemical that would react to antibiotics by changing color?
Zebnd0281
Posts: 5
Joined: Sun Oct 11, 2015 12:48 pm
Occupation: Parent

Re: Test strips for E Coli and Salmonella

Post by Zebnd0281 »

For my daughters science project she would like to create a method similar to the e coli/salmonella strip and create a way to detect harmful bacteria and possibly antibiotic reside in uncooked meats. How can she go about this?
SciB
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Re: Test strips for E Coli and Salmonella

Post by SciB »

Hi,

Thanks for sending the information. I took a look at the three products and the first is the only one that gives a result for both Salmonella and E coli, although I am not sure that you can distinguish one from the other.

The other two kits use antibodies to detect E coli only and I suspect they are quite expensive.

Detecting antibiotic residues on food would be difficult. There are a number of different antibiotics that may be used and unless you knew which one to test for you would have to assay for all of them. You might be able to set up a test using an agar culture of E coli and filter discs containing an extract of the food to see if it inhibited growth because of the presence of an antibiotic. Here is a similar project if you are interested: https://www.sciencebuddies.org/science- ... p014.shtml

What is the hypothesis of your project going to be? Are you going to leave cooked and uncooked meat at room temperature for various times and see which one has more bacterial growth? You could compare chicken, pork and beef and see which one is more likely to be contaminated with E coli and Salmonella. Or maybe compare national brands with less well-known brands to see if there's a difference in bacteria.

Good luck and keep us posted on what you decide to do so we can continue to help.

Sybee
Zebnd0281
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Joined: Sun Oct 11, 2015 12:48 pm
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Re: Test strips for E Coli and Salmonella

Post by Zebnd0281 »

Good Morning Sybee,

My daughters goal is to create either a test strip or a pad that can detect dangerous food borne bacteria and antibiotics. She then plans on testing local meats. We have read that in an Indole test Kovacs reagent is what indicates many harmful bacteria such as e coli by turning a purple color. Is that what is used in the test strips that are on the market? What causes the color change? I have read that there is a test for salmonella that would turn the strip yellow but I don't recall the name of it. Is there a similar color changing process to detect antibiotics? Any ideas would be much appreciated.

Here is a video of the two test strips that change color when they come in contact with e coli and salmonella. Its also on Youtube
http://www.bing.com/videos/search?q=vid ... 9C34B0B3C6
SciB
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Re: Test strips for E Coli and Salmonella

Post by SciB »

Good morning,

Sounds like you have chosen a pretty ambitious project. Do you have access to a lab to work in or are you doing this at home? If you need to order certain reagents they can only be shipped to an institution like a school or university, not to an individual. Also, what is your level of knowledge of biology and chemistry? I need to know this so I can explain things in a way that you will understand. The chemistry and methods can be pretty complicated.

With regard to the three kits you listed before, the last two work by means of an antibody to E coli and a color development system linked to the antibody. The first kit only said that their test measures an enzyme's activity which doesn't tell you much. Since these kits are manufactured by a company, the components and method are proprietary.

I looked up the Kovacs' reagent (KR) test for bacteria and found that it produces a color change in the presence of indole, a bacterial breakdown product of the amino acid tryptophan. The test is positive for E coli but not Salmonella according to the wiki: https://en.wikipedia.org/wiki/Indole_test

One possible problem I see is that the KR might not work properly in the presence of food. This is something you would have to try by just adding KR to the homogenized food that you are testing and seeing if you get color change. Also, I don't know how sensitive KR is. If their are too few bacteria in the food then you won't be able to see a color change.

I watched one of the videos and there was no explanation of the chemistry behind the test. When companies develop tests like this, their methods are usually proprietary--secret.

As for detecting antibiotics, I do not know of a single test that would work with all antibiotics. I gather that what your daughter is thinking of is a simple strip that will register the presence of antibiotics. It might be possible to make something like that for a single antibiotic, but you would have to have a pretty thorough knowledge of chemistry and access to a lab to do the work in. I think just focusing on the detection of E coli or Salmonella contamination would be your best plan.

I hope this helps. This is an ambitious project but certainly a useful one.

Good luck!

Sybee
Zebnd0281
Posts: 5
Joined: Sun Oct 11, 2015 12:48 pm
Occupation: Parent

Re: Test strips for E Coli and Salmonella

Post by Zebnd0281 »

Thank you for the reply. We do have access to a school lab and yes this is a very ambitious project especially for a 13 year old. She has narrowed her test down to just testing beef. Ideally she would like to test the beef (and this can mean water that has been soaked in the test beef) for e coli, salmonella, listeria if possible, and narrowing the experiment down to just one antibiotic. She has not been able to find the most common antibiotic given to cattle or which is most harmful to humans but Monensin keeps popping up so I think she is leaning toward that antibiotic. Her idea is to combine the tests into a common "kit" of sorts. With access to chemicals what would be the easiest way to test for salmonella, listeria, and the antibiotic Monensin?

Thanks again. You have been most helpful
SciB
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Re: Test strips for E Coli and Salmonella

Post by SciB »

Hi,

If you want to be able to indicate the presence of Salmonella, Listeria and monensin using test strips and color reactions it will have to be done on three separate strips. To accomplish it on one strip would be exceedingly difficult even for a PhD molecular biologist.

The way that commercial manufacturers create test strips for specific bacteria and viruses is by using antibodies that recognize molecules that only occur on one type of microorganism. The method is generally known as an ELISA which stands for enzyme-linked immunosorbent assay: https://en.wikipedia.org/wiki/ELISA

To create a test strip for Salmonella, you would first have to attach Salmonella-specific antibodies (Abs) to a substrate on the paper strip. Abs are protein molecules that have two ends. One end has the amino acid sequence that recognizes the bacterial protein and the other end is for immune system interaction. When the Abs are attached to the substrate they have to have the recognition end sticking out. This can be done but requires some chemical manipulations.

The Abs on the strip will bind to and trap the bacteria onto the test strip. Now in order to visualize the bacteria, you need to have a second type of Ab that recognizes Salmonella but has an enzyme such as alkaline phosphatase attached to the opposite end. The strip is put into a solution containing the Ab conjugated to alkaline phosphatase for ten minutes or so and then rinsed off. To produce the color, the strip is now placed in a solution of BCIP and NBT which are organic molecules with very long names (http://www.sigmaaldrich.com/technical-d ... aline.html)

Where there is Salmonella on the strip, there will be Ab-alkaline phosphatase and when you put the strip into the color development solution the enzyme reacts with BCIP to produce hydrogen ions that reduce the NBT to form an insoluble purple substance that is visible on the strip.

The same process can be used for Listeria and monensin provided you can buy the appropriate Abs. There are numerous sources of Abs online but the one that most scientists try first is called Abcam: http://www.abcam.com/
There is a search box and all you have to do is type in Salmonella, Listeria or monensin and you will get a list of the available Abs--then you can choose the ones appropriate to your needs. Remember that you need two Abs for each strip--one to capture the bacterium or antibiotic and one to produce the color.

Let us know if you have more questions.

Sybee
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