Bacteria in restaurants

[deleted-151606]

I am choosing a topic for my 8th grade honors science fair and have a few questions.

I was thinking about comparing food trays, at five fast food restaurants, to see which is the "cleanest/dirtiest". I know bacteria can be difficult to identify, outside of a lab, so should I keep it simple and not attempt to identify any of the samples? I'm thinking that I would take a swab on a tray at each restaurant, then clean the same area with an alcohol swab and re-swab (to have a controlled variable). Each would be in a petri dish (agar) so...10 dishes. What's the best way to state this? Should it only be looking for bacteria growth...the amount? I'm interested in this idea but am not quite sure the best approach. Would it be better to compare the trays to another item in each restaurant, like the bathroom faucet or door handle?

I appreciate any help you might be able to provide.

[deleted-143565]

Hello,
This is a very interesting idea for an experiment. You are on the right track with the idea that you would want to measure growth, NOT attempt to identify the organisms. That Is an advanced and potentially dangerous concept. For a control you can use simply an un- inoculated agar plate which should show zero growth . What you may need to consider is if you are measuring how clean the restaurant is, are you taking samples right after they have been washed or after people have used them? One is not the measure of the restaurant but the customers. Of course if the employees "wipe" the trays down , then you have a cleanliness issue to deal with.

To figure out the cleanest restaurant compare one variable against each other, if the trays are to variable pick another area. You may even consider comparing for instance, bathrooms in different types of facilities. Like restaurants, fast food, clothing stores, coffee shops etc. to see what type of establishment is cleanest. Just an idea.

If you stay with the trays;
Figure out which state the trays are in when you measure the growth, this will guide you to your hypotheses . Then the growth is measured by counting colonies growing on the plates.

Follow up with me if you have any questions.

Good Luck,

T.choate

[deleted-151606]

I was thinking my samples will be taken once the tray is given to me (which one would assume should have been cleaned in between each customer). I guess it could be more of "how much bacteria is on your food tray?" I plan to find out each restaurants policy of cleaning their serving trays as well as research the product material of the trays (the type of plastic) and how it relates to bacteria. I know certain surfaces are more likely to "keep" bacteria on them. I could actually do a cleaning product (lysol wipe, disinfectant etc.) for the second swab (controlled variable) to see how effective that product is at disinfecting. Is that too much? Do you think I should keep it to one subject?

Thanks for your help!

[deleted-143565]

This sounds like a good idea as long as their cleaning method is fairly similar because then you introduce another variable of
" which cleaning method is better" , in addition to which trays are the cleanest. Of course that could be an additional second hypothesis if you wanted. As far as the second wipe with a disinfectant, this assumes zero growth as a control but it might surprise you that you still may have bacterial growth and that you are comparing how well the disinfectant works, thereby indirectly measuring how dirty the trays still are. You see disinfectants don't work instantly which is a common misconception, but need what is called " contact" time to truly work. So decide what your variable or variables actually are, you may have more than one, and this should help you pick your control.

Good luck,
Hope this helps...

Let me know how you are doing

T. Choate

[deleted-151606]

Ok, I'm thinking that could get tricky but I will see if I can identify the exact cleaning method at each restaurant. I might need to just keep it to whether or not bacteria is present on the tray because I was always intending to sample a tray that is "given" to me as a customer, as a "clean" tray. Wouldn't that be what I could do and not introduce the cleaning method...like the idea of the door knobs at different types of places that you mentioned earlier. I wouldn't necessarily know how they are cleaned or how often. I would rather have a tray that they don't know I'm sampling. Of course they would heavily clean the tray if they know I'm going to swab it. So, I like the idea of getting what's really on the tray. I'm just trying to hurry up and narrow things down because I need to do my research paper and references.

I might think about the idea of the bathroom door knob at different types of places...could be interesting!

[deleted-143565]

Hello,
Yes, I did not want to complicate things for just give you something to consider that may be a variable. The idea of " how clean is my tray" from a customer point of view is interesting and perhaps " scary" if you think about it. I think you have a good grasp on what you want to do and how to proceed. Swabbing the trays to a plate for your tests, will give you a good idea of cleanliness like you mentioned.

The bathroom knobs etc. is promising also if you having trouble with the trays.

Great job with your idea. Good luck.
Let me know how your research is going.

T.choate

[deleted-151606]

Thanks so much for your help...I will keep you posted and definitely ask for advice if I run into any problems.

[deleted-151606]

I forgot to ask...can I name the restaurants in the project or should I say restaurant A, B, C, D & E?

[deleted-143565]

I think it would be best to stick with the letter naming just for ethics. However, in your lab notebook keep a record of which is which so if anyone asks you could reveal the information. You may want to check the science buddies forum to see if there is a specific rule about this.

Glad to help.

Looking forward to your results.

Lots of luck.

T. Choate

[deleted-151606]

I have questioned the managers at the restaurants and they all have similar cleaning methods...it will be interesting to see what the samples actually show, and to see how much bacteria actually grows from each of the five tray samples. None of the restaurants knew the manufacturer of their trays, and only one stated that Microban was in their trays. Honestly, I don't think they know where the trays came from or the material they are made of. I mentioned Microban in my research as a material which helps reduce bacteria growth in plastics.

When I take the samples from each tray should I just use a sterilized cotton swab? Does it need to be moistened in any way since the trays will be dry? Or do I swab straight on the tray with a dry swab? I will immediately transfer this to the agar petri dish but I wanted to be sure of the best method for swabbing. I do still plan to do a second swab after using Lysol to see the difference in the two samples.

Also, do my blood agar petri dishes need to remain refrigerated until I use them? Thanks again for any helpful advice!

[deleted-143565]

Hello,
First off yes, you must keep your plates refrigerated until you use them or the will most likely become contaminated. Also, on this note make sure when you incubate them they are upside down, in other words the top is face down or else condensation will form on the lid and drip onto the agar and interfere with growth. As far as swabbing it will be best to use a moist swab or else transfer will be difficult and samples will be hard to collect. You could just use distilled water to moisten your swabs ( or deionzed) like contact lens solution or you can buy distilled water, NOT spring water or drinking water. These types of water should be bacteria and contaminant free. Make sure your swabs are moist enough not dripping wet.

I don't know that the Lysol is necessary unless you are actually conducting two experiments. This is actually a second test. But that is fine if you choose to do it that way.

Make sure you have a control ( such as a plate that is not inoculated). As Lysol would not be a control but a test.

Good luck sounds like you have a good grasp on things !!!

T. Choate

[deleted-151606]

Great, thanks! That is how I have the agar plates now. I will be sure to use the distilled water when sampling and will have a control petri dish for each tray (no sample in it). I think I will skip the Lysol and keep it to the 10 petri dishes...5 with samples, 5 as controls. I really appreciate your help...thank you!

[deleted-151606]

I am not sure how to write the variables (independent, dependent & constant) for this. Are the independent: the 5 restaurants, 5 food trays, distilled water, sterilized cotton swabs & agar petri dishes? Dependent: the amount of bacteria that grows from each tray sample. Constant: Should this be the same as the independent??? Thanks!!

[deleted-140482]

Your independent variable is the factor that you are changing in the experiments, so you are correct that it would be the restaurants, because you are changing which restaurant each tray is from. This does not include things like distilled water, cotton swabs, and petri dishes. Those would be closer to controls, or controlled variables, which the investigator keeps constant throughout. In your case that would tend to be the area of each tray swabbed, the amount of time and the temperature you let the petri dishes grow at, etc. Those could include the cotton swabs, type of petri dishes, and distilled water, etc. The dependent variable is the variable that you do not control, so again, you are correct that this would be the amount of bacteria that grew.

[deleted-151606]

I took my petri dishes to the school lab this morning, for my experiment. How long should I leave them there for the bacteria to grow? Thanks!

[deleted-140482]

Obviously this depends somewhat on the exact type of bacteria, etc., but for the most part you should see good bacterial growth overnight (~18hrs) at 37 degrees Celsius (~98.6 degrees Fahrenheit). If you are keeping them at room temperature it will take considerably longer.

[deleted-151606]

What is the best way to count the colonies on each petri dish? I have looked at the page about interpreting plates but want to be sure each one is done correctly and the bacteria is "measured' correctly. I tried to attach photos but my files were too large...going to try to make them smaller and send later.

[deleted-151606]

Attached is the first of five photos. Need to change the file extension from a .doc to a .JPG

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Attached is the last of five photos. Need to change the file extension from a .doc to a .JPG

[deleted-140482]

I looked at your photos, and you shouldn't have any problem just literally counting the colonies. The big, "fluffy" circles are actually fungus (contamination), so they should NOT be counted as bacteria, although I think they will be worth mentioning in your project. It's hard to know whether the fungus was actually on the restaurant trays or are contamination that happened later (when you store bacterial plates for awhile, fungal contamination can be a problem). Regardless, it's the smaller (non fuzzy) colonies that are bacteria. I would count them for each plate and then you report that number as colony forming units (CFUs). Obviously you have more than one kind of bacteria on some of your plates, so you could report a total CFUs and also break it down by kind. There's no way for you to truly definitively identify what each kind of bacteria is in this situation, but you could just call them "bacterial strain 1," "bacterial strain 2," etc. Just for fun, I would venture a guess that the fairly yellowish, small colonies could be Staphylococcus aureus, but again there's no way to confirm that just from looking at the plates.

Hope this helps!

[deleted-151606]

Thanks for the information...very helpful. I did the plates all in one day and immediately took to the school lab, so I'm hopeful that what was on each plate came from the trays. And my control (which I did not send of a picture of) is clear of any fungus or bacteria. They were in the lab for 5 days but started growth by 3 days. I agree with the Staphylococcus from the different sites I've looked at for comparing. I know I can't name any specifically but I will make some observations of possibilities and maybe include similar photos to show comparisons. Do you think that would be a good idea? Some also looked like types of yeast. Gross!

[deleted-140482]

It's great that your control plate was clear. With that added information, I agree that it's highly likely the fungus actually comes from the restaurant trays. I think it's a great idea to make observations of possibilities and include similar photos for comparison. As long as you aren't claiming that a specific colony is definitively a certain type of bacteria, I think you are free to suggest possibilities as much as you'd like, and it will really add to your science fair project.

Looks like your project went really well, and I agree that the results are gross.

Good job!

[deleted-151606]

I realize the due date for my project is listed as october 1, which is incorrect. When i started i listed the due date for the first part of my project and I'm not sure how to change that now. So...I am not getting anyone to answer the question listed below. The final due date for my project is January 3 and i need to due these data tables immediately. Our teacher breaks down the project into sections and each area due is spaced out over time. Please have someone answer my question. Thanks!

I was wondering the best way to chart my results...I did a data spreadsheet but with 5 restaurants and the breakdown of 17 different strains and 3 fungi it was a little confusing, I think. I want the results to be easy to read and interesting to the eye. Any suggestions? Thanks so much!