What type of cleanser/ disinfector disinfects /cleans your hands the best?
I thought liquid hand sanitizer was going to disinfect / cleans the best because when you put it on hands the smell lasts for a long time and after hours when you wash your hands to eat you can sometimes also get the taste of it. Both the smell and the taste are really strong which made me think it would be more effective.
While doing research about my experiment I came to know that nutrient agar is the medium that can be used to grow bacteria. The manual count method was not that efficient for the merged colonies then I came to know about the grid method from further research and printed a grid pattern and put it under a petri dish to count each colony under one square as one colony. While going deeper in the research I came to know that professional researchers use apps like CFU that can count bacterial colonies automatically to make work easier. I just installed it on a phone and clicked pictures of the petri dish and it gave me a count of colonies. This was an easy method but in my case, the drawback was it didn't count the merged and coloured colonies. While doing research I came to know that scientists use the serial dilution method to count the colonies more accurately. If I get another chance to do the same project again I would use the serial dilution method.
Variables: Disenfecters, Petri dishes, Amount of lines you make on the petri dish, Amount of colonies.
Variables to keep the same: Disenfecters, Amount of lines you make on the petri dish
Variable to change: Amount of colonies
1. Take four Petri dishes and label them and their lids.
2. Take a pot and add 8 grams of nutrient agar in 375ml distilled water at room temperature.
3. Stir it well periodically and bring it to a boil.
4. Cool at 50 *C and portion equally into Petri dishes
5. Cover immediately and let the agar cool down (for 30 - 40 mins).
6. Take the bar soap and wash your hands with it and dry with a paper towel (make sure the soap is untouched and so are the paper towels).
7. When hands are properly dried, swab the palm of your hand.
8. Gently roll the swab on the petri dish in a zig-zag pattern.
9. Cover the peri dish with its lid.
10. Touch different surfaces and after a while repeat the same process for the liquid soap.
11.When you are done with the liquid soap touch the different surfaces and Spray the liquid hand sanitizer onto your hands.
12. When hands are properly dried, swab the palm of your hand.
13. Gently roll the swab on the petri dish in a zig-zag pattern.
14. Cover the peri dish with its lid.
15. Touch different surfaces and after a while repeat the same process for the gel sanitizer.
16. Put all four labelled Petri dishes in a dark and warm place like a closet.
17. Make observations every day and keep records of what you see growing in each dish.
18. Take the final observation after 5 days and note down the results.
I have used two observation methods to count the colonies.
Manual count: I counted each dot as one colony and for the merged colonies I have used the grid method. The grid method is when you draw or print a grid on a piece of paper and put it under the petri dish and then the amount of the colony that comes in the grid would be counted as one colony.
CFU app count: While I was researching I found out that there are apps that count the colonies for you. You need to download the app on a phone and then take a picture of the petri dish and let it load. The colonies will be circled red and there would be a count on the bottom. After taking a few pictures I realized that it doesn't count the big, coloured and merged colonies.
Here is my data for the number of colonies formed in petridishes in the the form of a Bar Graph and a Table. Pastel pink colour is for Manual count data and mint green colour is for CFU count data.
Disenfecters / Cleansers Manual Count CFU Count
Liquid Hand Sanitizer
Gel Hand Sanitizer
Liquid Hand Soap
Conclusions: The least bacterial colonies were formed in the bar soap petri dish so therefore it is the best disinfector/cleanser. In conclusion, the bar soap best disinfects your hands.
My experiment would help people to make better decisions about what type of cleanser/disinfector they should buy to clean their hands with. This will help them to save money and stay away fro viruses.
Sources Of Error
Although this experiment went great, I had a little problem in manually counting the merged colonies (the unseparated colonies). This could be the source of error in my experiment. That is why I have used the second observation method (CFU App) to cross-check the placing for all the four cleansers used in the experiment.
1. Bacteria growing experiments in petri plates. (n.d.). Retrieved March 14, 2021, from
2. Hand sanitizer. (n.d.). Retrieved March 14, 2021, from
3. How to grow BACTERIA: 5 experiments to grow & TEST BACTERIA. (2020, October 15).
Retrieved March 14, 2021, from https://learning-
4. Sieuwerts, S., Bok, F., Mols, E., Vos, W., & Vlieg, J. (2008, September 05). A simple and fast
method for determining colony forming units. Retrieved March 14, 2021, from
5. Serial dilution. (2014, September 09). [Image]. https://i.ytimg.com/vi/loyeVy1D-
6. TheFunsuman. (2014, September 09). Serial dilution. Retrieved March 14, 2021, from
I would like to express my special thanks to my teachers Mrs. Richards and Mr. Christie for their valuable guidance and time. I am very much thankful to my school principal Mr. McConney who arranged the science fair. I am extremely grateful to the science fair teacher Ms. Aulakh for introducing many new things related to CYSF.
I would like to express my profound thanks to my parents who helped me during the whole experiment by taking the pictures and paying for the petri dish kit.