Science Buddies: "Ask an Expert"

I am doing the 'how well do disinfectants work?'' science project.

I understand how to do it but now I want to add an extension to make it more complex.
So I've already found out what is the perfect disinfectant and now I want to add something like maybe a small experiment to find out something new related to the disinfectant topic.

I was thinking about maybe a small experiment to differentiate whether hand sanitizer is better than regular soap.
Any more ideas?

Please help! Thanks!

Hi XtremeScience,

This is a great project and it's good that you are thinking about extending the investigation. Have you already done the project as described, or are you trying to design a unique project of your own?

The basic experimental design, which includes contaminating a cutting board and then marking sections for treatment after overnight incubation is a good one, so I would not change that part too much. It's hard to get quantitative results from a microbiology project and the experiment as described should work well. Here are some variations of the experiment that you might try:

1. If you have the prefect disinfectant, try different concentrations of the product. Use the disinfectant as described and also test a higher concentration and perhaps two or three samples with a more diluted product.

2. Your idea to use hand sanitizer and regular soap would work also; trying a variety of products would make an interesting project. Look at the product labels and pick products that have different ingredients.

3. Or, you could try sanitizers with a range in prices. Do more expensive products work better?

You can make your project better by running samples in duplicate and repeating the project to make sure results are reproducible. Also make sure all other parameters such as temperature are controlled. And don't forget to include controls in your experiment. For this project, you will need both a negative and positive control.

Please let us know you have any questions. Good luck!


Donna Hardy

Thank you so much for you help Donna!

No, I am still doing my research paper so I haven't done the experiment yet. I like the main concept in the procedure however I would like to change it a bit and maybe add something else to improve it and make it suitable and more complex. The main reason is because the head of the science fair wanted me to participate and he expects me to do something impressive and difficult.

Anyways, I do like the first idea you gave on the different concentrations of the perfect disinfectant.
Also, 2 more questions...

1. For the 5 disinfectants, what would you choose as a good variety to test each disinfectants' ability? Would you choose strong concentrations and some dilute ones too?

2. For the hypothesis, I predicted the perfect disinfectant would be bleach. Do you agree? Why? If you don't can you pick one from the list you wrote above as the perfect disinfectant and a reason for it?

I appreciate your help in this matter,

Xtreme Science

Hi XtremeScience,

Thanks for the additional information; this is helpful.

You are right; bleach is bactericidal; it always kills bacteria without exception. However, it is also toxic to humans and the environment, so it causes other problems if it is used routinely. Bleach would be a good control to use to verify that all of the bacteria in your sample are killed. Your hypothesis is correct; bleach will always work as a disinfectant.

Here is a link to a summary of how bleach works. Bleach kills bacteria by unfolding proteins that are needed for cell function.

https://publications.nigms.nih.gov/insi ... teria.html

For your science project, you might think of a problem that needs to be solved by killing bacteria. Perhaps this could be a study of the least toxic way to sanitize kitchen counters, bathrooms, hands, soiled clothing, grocery cart handles, or something else. Think of something that is important for you or your family. For example, I just read an article on the new Norovirus that has appeared in the US:

http://insightticker.com/2015/12/27/296 ... -vomiting/

You cannot do any work with a pathogen like Norovirus, but perhaps you could do an indirect study that would help you avoid this virus this winter.

Once you have the problem identified, you can continue your background research and design your experiment. For the selection of products, I recommend reading labels and pick products that have different ingredients. For example, hand sanitizer will usually have ethanol; bactericidal soap will usually have Triclosan as the antimicrobial ingredient. You want to evaluate a variety of products.

Next do more background research on the toxic properties of all of the bactericidal ingredients. Look for information on the toxicity of each product and try to rank your product selection based on toxicity to humans or to the environment. For your background research, you will need scientific articles or information from manufacturers. You can request the MSDS or material safety data sheet for each product for specific hazardous information.

Your idea of doing a more complicated project is understandable, however, your project should be a well controlled experiment designed to answer your project question. It does not have to be complicated. You just need to have a single very well designed experiment that will answer the question. And you need to do the experiment twice to show that results are reproducible.

For each product, you should follow instructions for use as provided by the manufacturer. If you wanted to make it a little complicated, maybe you could also try 1/2 concentration or try two different exposure times, but don't do more than that.

So your project might be to find the most effective/least toxic product that will answer your project question. You will distinguish your project with amazing background research and with a meticulously designed and executed experiment. Does this make sense?

Please let me know what problem you want to solve and let me know if you have any questions about my suggestions.
Do you want to revise your hypothesis?

One more question. What are you going to use for a negative control?


Donna Hardy

Hi Donna,

Thanks for the suggestion. I like the idea 'to find the most effective/least toxic product' but should I now have to change the project title 'How well do disinfectants work?'
I chose for the 5 disinfectants: Bleach, alcohol, hand sanitizer, regular soap and lysol. What would you say?

Also, you said repeat the experiment twice, I am doing the experiment after school in the schools' lab using the schools' agar plates and since I am using 6 of them, I don't think I shall be able to use more.

For my negative control, I chose water, is that a good idea?
Should I use the same procedure for the experiment? Or should I change the cutting board to a different fomite?

There is no need to revise hypothesis but as the most effective/least toxic product what do you think?

Thank you so much,
Xtreme Science

Hi Xtreme Science,

What Lysol product are you using? According to Wikipedia, Lysol can contain either benzalkonium chloride or hydrogen peroxide as the active ingredient. Can you check the label on the bottle of product you are planning to use? Either product would be fine, but you need to know so you can look up the mechanism of action for the specific ingredient you will be testing. .

https://en.wikipedia.org/wiki/Lysol

The hand sanitizer probably contains alcohol, so check that label also. If so, there would be no difference in using hand sanitizer and alcohol. You should pick 5 disinfectants with different ingredients. Another choice would be bactericidal soap, which usually contains Triclosan, or your could use the two different types of Lysol.

Look up the directions for each product. For a controlled experiment, you will either need to use each product the same way, or follow the manufacturers' specific instructions for each product. Do some additional research so you can decide the best way to do the experiment.

What regular soap are you using? There are a variety of ingredients in soap. I know you haven't had a chemistry class yet, but let me know the ingredients and I'll explain

You can focus on doing background research on the mechanism of action of the ingredients and the toxicity/ safety of the ingredients. Also, do try to define your specific purpose. Finding the best disinfectant to use is a fairly vast topic for a science project. I think it would be useful to define the application as this would give a better focus for your project.

Controls. For your experiment, you need two controls, a positive control with no treatment to show how many bacteria were present without disinfectant. And you need a negative control, which is not inoculated so show that your agar plates were sterile and that any bacterial growth was not the result of accidental contamination. So you will need seven agar plates to use. If you can only get six, then it would be best to include both controls and test just 4 products.

When you get back to school, talk to your teacher and ask if you can get more agar plates. If not, then you will only be able to do the experiment one time. You can address this in your discussion section and explain that you know that it would be repeat the experiment, but you could not because of lack of materials. The science fair judges will give you credit for thinking about it.

Are you going to prepare the agar plates or will you be using commercially prepare plates? What growth medium will you be using? You need to include a description of the agar and explain what it contains that support the growth of microorganisms.

Donna

Hi Donna,

Should I use the same procedure for the experiment? Or should I change the cutting board to a different fomite?
When I leave the fomite overnight so the bacteria can culture, can I leave it where I want or does it have to be in specific conditions?

For the 5 disinfectants, I'm thinking of 'clorox bleach' since one of its ingredients, sodium hypochlorite, is used to whiten and kill bacteria.

If the bactericidal soap includes a smell for washing purposes, does it affect the efficiency of the soap? Maybe dettol or lifebuoy would work. Also instead of alcohol, it might be better to use hand sanitizer since the active ingredient in the ones I have is ethanol 68%. Any more ideas for disinfectants?

Xtreme science

Hi XtremeScience,

You have some good questions and it's good to think about the details at this time, before you do the experiment..

In a science experiment you want to control all parameters except one independent variable, which for your experiment is the disinfectant. You can use a cutting board or another surface, however, you need to make sure that all samples are taken from the same surface and handled the same way. So choose a surface and method that is convenient for you, but make sure every sample is treated exactly the same.

You should look at the label for Chlorox. The main ingredient in every bleach is the sodium hypochloride, but Chlorox contains additional ingredients that help with cleaning. If you use Chlorox, you will be testing the effect of the combination of ingredients, not just the sodium hypochlorite.

What concentration of bleach are your going to use? What will you dilute the bleach and the other products with?

The same principle applies to the soap; if the soap contains a fragrance, you will be testing the effect of the combination of all ingredients. You cannot assume that the results are due just to the soap. For purposes of a science experiment, it is considered better to test one component at a time separately, but this will probably not be possible for you to do. However, remember this and include it as a discussion point in your analysis section.

Donna

Hello! Sorry to bother but I have a few more questions left...

1. Would the cutting board be a good fomite for this experiment or would you recommend another one?

2. For my extension, I am doing a small experiment related to the project on disinfectants. Which one would be suitable?

-Hand sanitizers vs regular soap and water
-Where are the most germs in your house?
-Are anti-bacterial soaps better than plain soaps at reducing bacterial contamination?

3. What indications set bacterial colonies apart?

Thank you so much for all your help,

Xtreme Science

Hi XtremeScience,

1. The cutting board is a good choice and the method for contaminating it with bacteria will work well. However, if it is not easy for you to get a cutting board, you can use a different surface. Exposing the surface to the lunch meat and leaving it overnight at room temperature is a good way to get a significant number of bacteria so you will have results in your experiment. This part of the experiment should be carefully controlled so every sample is treated the same way. Don't do different samples at different times. Write down exactly what you do so someone would be able to repeat your experiment exactly as you did it. It is helpful to take photos to document the procedure.

3. Bacterial colonies are discrete dots on the surface of the agar. Here is a link for additional information for interpreting bacterial colonies:

https://www.sciencebuddies.org/science- ... ates.shtml

2. I recommend that you don't do any side experiments. From my experience as a science fair judge, I can tell you that the best thing you can do is to do a well designed, controlled experiment with one independent variable (the disinfectant) and measure the results (your depdendent variable) and make sure that all other parameters are controlled. Your project needs to have a purpose that is answered by your experiment. .

Read through the different sections of the project guide from this website to make sure you know what to do:

https://www.sciencebuddies.org/science- ... ndex.shtml

If you do a side project that is not quite related to your main question, the science fair judges will have a hard time figuring out what you did and why you did it.

If you want to do something extra, the following will improve your project:

1. Repeat your experiment. Science experiments should be reproducible. If you can't do this, explain that you wanted to repeat results, but could not.
2. Your small experiment ideas are interesting topics and you could include them in your background paper; you could also mention them in your discussion section when you are talking about what you might do in the future. .
3. Make sure you have a bibliography with scientific papers cited. Many students overlook this detail.
4. Think about what you can do to make your project board more attractive. A neat well-presented project will help the judges understand your project.
5. Read the microorganism safety guide from this website to make sure you will be able to do your project safely:
https://www.sciencebuddies.org/science- ... fety.shtml
6. Check with your teacher and find out if you need to get approval from the Scientific Review Committee for your project. You would not want to do this project and be disqualified at the time of judging.

https://www.sciencebuddies.org/science- ... _src.shtml
7.. Become an expert in your topic. Make sure you know as much as possible about the each disinfectant and how it kills bacteria.

I hope this helps. Let me know if you have more questions.

Donna

Thank you so much Donna for your tips! I really appreciate it.
I know exactly what I am doing now and will get straight to it.
With all the background research, extra information and tips, my project will be attractive, informative and precise.

Yes, I did need approval from my science teacher before I started the experiment.
I'll come back to you when I have another question,

Xtreme Science

Hi XtremeScience,

Thanks for your reply. I do think you are on track for a great project now, but do let me know if you have any other questions.


Donna

One more thing....

When I find out the perfect bleach, is it a good idea if I check how effective it is on different fomites using agar plates? e.g. kitchen sink, bathroom equipment, door handles, etc.

Thanks !

Hi XtremeScience,

Bleach will be used as one of your independent variables and you will compared results other disinfectants. You should not use different surfaces, such as door handles or the kitchen sink as that that would be a different experiment. Just use one surface and different disinfectants. Everything else in the experiment should be identical.

Or, you could use one concentration of bleach and test it on different surfaces. However, since bleach is a well documented bactericide, this experiment would not be as interesting as other experiments. I would expect that bleach would work very effectively on any surface.

It might be helpful to review the information on variables from this website.

https://www.sciencebuddies.org/science- ... test.shtml

Please do keep me informed about your progress. I will be very interested to hear about your results, or answer any other questions.

Donna

1. What should I use as a negative control? Water?

2. Also, for the procedure of the 'how well do disinfectants work' science buddies project they say:

swipe the cotton-tipped applicator gently across the agar surface using a zig-zag motion.

I looked at this website:
https://www.sciencebuddies.org/science- ... tion.shtml

Should I just swipe the agar plate in a zig zag motion throught the whole agar plate? Or is there a better way?

3. Should I use hand sanitizer or ethanol for one of my disinfectants? The hand sanitizer I might use contains 50% + ethanol.

Hi XtremeScience,

You should use just one; either hand sanitizer or the ethanol. Since hand sanitizer is a product that people use, and there might be restrictions on your using ethanol in a science project, I recommend that you pick the hand sanitizer.

What other disinfectants will you be using?

Donna

I will be doing my experiment on 18 January. I really need some help on the disinfectant part. I have my positive and negative control.

Already, I've chosen:

-Clorox
-Hand sanitzer

I NEED 3 MORE! Can you help me with ideas? Please be precise with the exact disinfectant products.

What do you think about isopropyl alcohol and regular soap?

Hi XtremeScience,

Since you can only choose a limited number of disinfectants, I think that choosing products with different chemistries would work the best. Isopropyl alcohol is very similar to ethanol found in hand sanitizer. Regular soap is a good choice. Perhaps you could also use Lysol and a soap with an antibacterial agent such as Triclosan. It might be worthwhile to go to a grocery store and check out the labels, or read the labels of any products you have at home. Look for products that have something other than an alcohol or soap in them.

You also need to decide what concentration of each product you should use. To be safe, you can read the label and follow the directions provided on each project. Regular soap and hand sanitizer are usually used undiluted, but Lysol and bleach are usually diluted. What concentration will you use?

Donna

Hi Donna,

Thanks! Well, the science buddies project idea also recommends 5 disinfectants and water only.

So for hand sanitizer and the soap, there won't be any dilution needed. However for the bleach I am using, it says:
'using 2 teaspoons of Clorox® Regular-Bleach per gallon of water.'

Although Triclosan is extremely toxic and it is advised not to use it in regular soaps, I do know a few soaps contain it as an active ingredient.

Now I need 2 more disinfectants, I was thinking dettol since it has benzalkonium chloride and no alcohol.

If I use another disinfectant, which is suited for another cleaning purpose e.g windows, would it still work on disinfecting the fomite of a cutting board?

Hi XtremeScience,

Detol contains 4.8% chloroxylenol (C8H9ClO), an aromatic disinfectant. with the rest made up by pine oil, isopropanol, castor oil, soap and water so it does not contain a quaternary amine. However you do not have chloroxylenol in any of the other products, so it's a good choice. For your last disinfectant you could use one that does contain a quaternary ammonium ingredient, or you could use Windex, which contains 2-hexoxyethanol, isoporpanolamine, sodium dodecylbenzene. lauramine oxide, and ammonium hydroxide. These are all described as cleaning agents, not disinfectants.

For your experiment, the water is a control, which should allow maximum growth of the microorganisms. You will compare the quantity of bacterial colonies growing in the water control compared to all of the disinfectants.


Donna

Hello!

Thanks for your suggestion! For the last disinfectant, you suggested windex. I thought of that as well but isn't it a windex a glass cleaner? Would it be suitable for disinfecting a plastic cutting board?

Anyways, thank you so much for your additionally research and time you spend for my project. I appreciate it!

Hi Xtreme science,

You are correct; none of the ingredients in Windex are classified as disinfectants, however, there are ingredients that would affect the stability of bacterial membranes, and this type of product is commonly found in the home. Also, the ingredients are different than the other products you are using. If you use a different brand of window cleaner, you will need to check on the specific ingredients.

It's your project, so you can decide what to use. The window cleaner would be a good choice. Or, if you want to limit your testing to only disinfectants, you will need to find one that contains a quaternary ammonium compound.


Donna

Yes, I actually want to use windex since it is also a hard surface cleaner. When I write the procedure, am I supposed to add that windex is not a disinfectant? Would this be testing a combination of cleansers instead of testing the efficiency of disinfectant specifically?

Thanks a lot! You're a great expert! I will come back with further questions if necessary!

EDITED: I don't know if this is bad but I really feel like changing my project now into germ invasion! I've been looking at it for a long time now and I am quite interested in it! It looks like the one I wanted on microbiology. My science teacher doesn't mind if I change it now either. I have 2 weeks and a few days left but if I change it, I'm sure I can finish it in time.

Please HELP!!!!

Hi,

Yes, in your background information section, you should explain that Windex is not a disinfectant and that it contains several cleaning compounds. You should do as much research as possible on all of the products and describe each ingredient and its effect on microorganisms. In your project, you will testing the effect of 5 products containing different ingredients.

You should also consider doing additional background research on toxicity of the various products. You can request the material safety data sheets on each product and look for scientific papers reporting human or environmental toxicity. You could include this in your discussion section when evaluating your results. If you find that all of the disinfectants are equally effective in eliminating bacteria, you could report the least toxic product that works to kill the bacteria. This would make your discussion more interesting.

I like the new title; it doesn't commit to any specific group of products like disinfectants and it will get the attention of anyone looking at the board.

Donna

Thank you! However, I don't mean about the title 'germ invasion' I want the whole science project.

https://www.sciencebuddies.org/science- ... p007.shtml

This is the website and I feel like doing this experiment instead of disinfectant? I really feel as though this project on -germ invasion- is much more intriguing than the disinfectant one. This one is what I prefer.

I have 2 weeks and a few days now until the deadline but my experiment is due for Monday to complete.

Should I use do that project or stick to disinfectant to keep safe?

Hi XtremeScience,

Thanks for the additional explanation. The germ invasion project is definitely an intriguing project idea and would make an excellent experiment. The materials are the same, so you would only need to change the experimental set up. You would learn a lot with either project. This is your science fair project, so you should decide which one you want to do. If you really like the germ invasion project, then it is probably the best choice for you.

Here are some additional comments that may help you make a final decision.

1. First check with your teacher to see if it is OK to change your project. If your original protocol has been approved by a scientific review committee, then it will not be possible to change.

2. You will need to redo your background research and procedure section. Will you have enough time to research the topic of microbial diversity?

3. How much time will you have after you set up the plates? Microbes from the environment can grow slowly, so it may take a few days for colonies to appear.

4. It is going to be more challenging to graph the results of this experiment. With the disinfectant experiment, your results would be more clear cut. How will you present the results of a microbiogical survey?

5. What is the purpose of your new experiment? What research question are you trying to answer?

Good luck! If you run into any other difficulties, it's definitely OK to keep the original project idea. Let me know if you have any other questions.


Donna

Hello! Yes, I do think the 'GERM INVASION' project is suitable. I will be doing it.

-As for your questions, I did check with the teacher, he said it's fine. Also, he said their are 15 agar plates he can give me meaning I'll have to ask him for more or if not, I need to decrease a few things.
-After I set up the agar plates, it says in the procedure '3 weeks' but I think I can check regularly during school. I will keep the agar plates in the schools' incubator so whenever I see them I shall notice if the colonies are visible enough so I can record my data. The longest I can take is around 2 weeks.
-I think I can do my background research on microbial diversity in time for the science fair.
-Maybe a bar chart including the different agar plate and the number of colonies. Or maybe a line graph. I could also do a flow chart.
-Question: What is the worst place where bacteria can culture in your home? or Where are the most germs at home?

My only question is:

Q1. Instead of choosing different sites e.g. bathrooms, kitchens, etc to put the plates in for 3 hours. Can I test different items using samples from a cotton-tip applicator and and zig zagging it onto the plate?
I chose a few:
-Toilet seat
-Laptop keyboard
-Kitchen sink
-phone
-toothbrush

Q2. Instead of leaving the plate for 3 hours, can I leave for 1 day or more?

I really appreciate your co-operation to my project!

Hi XtremeScience,

That's good news that your teacher approves.

With 15 plates, you can do one negative control and 7 samples in duplicate. This is good news also.

It would be best if you could do the 3 hour exposure as recommended in the experimental procedure. When agar plates are exposed to air, the microorganisms will float in and grow to make distinct colonies. If a cotton swab is used to collect microorganisms, the agar plate can get too wet and this will allow the microbes with grow all over the surface of the agar without making distinct colonies. However, a cotton swab could be used if necessary, but you would have to do the procedure the same way for every sample and plate.

Don't leave the plate open to air for more than 3 hours or it might dry out, and then nothing will grow.

Also, you should be aware of the effect of temperature on the growth of bacteria. if your school incubator is at 37 degrees C, you will only be able to grow microbes that can survive on human and other warm-blooded animals.. You will be more likely to grow microbes that are pathogenic.

If you use a temperature of 20 to 30 degrees Centigrade, more diverse organisms will be able to grow, including some molds. Since this project is about biodiversity, it would be better to use a lower temperature. However, the microbes will grow slower, but if you have up to two weeks, this should allow plenty of time to get results.

Why don't you pick a theme for your project, like home, school, or a local park and study the biodiversity in that environment? Or pick 7 different bathrooms or 7 kitchens. If you pick an outdoor location that is normally exposed to sunshine, you should get more pigmented colonies.

Donna

So do you mean I can't do the items I listed? I can not use those to check the dirty places in your home?
I really would like to use a sample from different items and see those on an agar plate.

Thanks

Hi XtremeScience,

You can choose the test the original items, however I do have a precaution for you. If you take a sterile swab with water and use it to transfer bacteria from the surface of the object and smear it on the plate, it will be much easier for the bacteria to float across the wet agar plate and grow together instead of growing as individual colonies.

The point of the biodiversity project is to observe the variety of individual colonies that grow on the agar surface and you can get individual colonies if you let the microbes float in from the air. It is extremely difficult to analyze plates that are completely covered with microbial growth. and one of the important parts of your project will be the analysis of the data.

If you do use a sterile cotton swab with water, then your control would be a water only plate; if you use a 3-hour air exposure to collect the microorganisms, then your control would be a sealed plate with no air exposure.

You could open up the plates near the objects you are interested in as an alternative if you want to. Perhaps use plate in each room of the house during the same time period.

I hope this explanation helps.

Donna