Does Antibacterial Hand Soap Kill More Bacteria Than Non-Antibacterial Hand Soap?

Researched by Jennifer W. 
2003-04



PURPOSE

The purpose of this experiment was to determine if antibacterial hand soaps are more effective at killing bacteria than non-antibacterial hand soaps.

I became interested in this idea because microscopic life has fascinated me for a long time and I am concerned about human health and disease.

The information gained from this experiment would help large institutions such as hospitals, schools, and homemakers, if there is no difference people will want to know this so they don’t spend extra money or time on getting antibacterial hand soaps.

 


HYPOTHESIS

My hypothesis was that there would be no difference between antibacterial hand soaps and non-antibacterial hand soaps on killing bacteria. 

I based my hypothesis on a statement made by Elaine Larson, a professor at Columbia University School of Nursing, after studying whether it matters if the hand soap is antibacterial or not on killing germs. “There wasn’t any difference in the bacteria counts on the hands between those who used the antibacterial or the plain soap.” 

 


EXPERIMENT DESIGN

The constants in this study were: 
* The amount of Antibacterial hand soap  
* The amount of non-Antibacterial hand soap 
* The amount of bacteria put on the agar plates 
* The temperature of incubator 
* The way the bacteria are applied to the agar plates. 
* The way you grow the bacteria. 
* The size of the agar plate. 
* The way the soap disc’s are applied to the plates. 
* The way the bacteria are measured. 
  
 

The manipulated variable was the antibacterial hand soaps and the non-antibacterial hand soaps.

The responding variable was the amount of bacteria killed.

To measure the responding variable I will measure the death zone diameter of the bacteria with a caliper ruler.

 


MATERIALS 
  
 

Quantity ITEM DESCRIPTION
3 Swab
6 Pipette
3 agar plates
1 Caliper ruler
3 Antibacterial hand soap
3 Non-antibacterial hand soap
9 Test tube
18 Soap discs
10 Milliliters of soap
1 Incubator

 


PROCEDURES

1. The microbiologist isolates and grows a strand of three different bacterial cultures.  
a. Escherichia coli  
b. Staphylococcus aureus  
c. Staphylococcus epidermidis 
2. Mix the selected colony type in sterile salt water. Adjust the suspension to a .5  McFarland turbidity visually.  
3. Soak a sterile swab within 15 minutes of adjusting the suspension. Rotate swab several times, pressing firmly on the inside wall of the tube above the fluid level. 
4. Swab the entire surface of the Mueller ?Hinter agar plate three times, turning the plate 60 degrees between streaking to ensure even distribution.  
5. Measure 10 micro liters of soap onto test disks. 
6. Dispense the soap discs on the surface of the inoculated plate 
7. Invert plate with the lid on and tap gently to be sure that all the discs stay on the agar surface. 
8. Place the inverted plate in 35 degrees Celsius non-CO2 incubator within 15 minutes of disc application. 
9. Incubate plates for about a day. 
10. Examine the plate a few inches above a black nonreflecting background with reflecting light. Measure the diameter of complete inhibition as detected by the unaided eye. The caliper ruler is used to measure the diameter of the death zone of the bacteria in millimeters.  
11. After all the bacteria tests have been done, kill all the bacteria you have worked with. They should be autoclaved using the standard hospital procedures.

 


RESULTS

The original purpose of this experiment was to determine if antibacterial hand soaps are more effective at killing bacteria than non-antibacterial hand soaps.

The results of the experiment were that antibacterial hand soaps work better at killing bacteria.  On average the zone of death was 51 millimeters for antibacterial but only 22 millimeters for non-antibacterial hand soaps.  
 

See the table and graph below.

 


CONCLUSION

My hypothesis was that there would be no difference between antibacterial hand soaps and non-antibacterial hand soaps on killing bacteria. 

The results indicate that this hypothesis should be rejected.  In fact antibacterial hand soap was more than twice as effective.

Because of the results of this experiment, I wonder if these soaps would have similar results against other species of bacteria. I also wonder if other soaps on the market would be more effective. It would also be interesting to test various antiseptics instead of soaps. 

If I were to conduct this project again I would do more then one trial for each soap/bacteria combination. Also I would use more kinds of soap.

 


Research Report 
 

Introduction

Bacteria can cause infections and diseases. That’s why washing your hands is so important. Knowing whether Antibacterial hand soaps work better at killing bacteria than Non-antibacterial hand soaps is important for people concerned about health. 

Bacteria

Bacteria are simple organisms that consist of one cell. They are one of the smallest living things. Bacteria are classified as prokaryotes. There are many types of bacteria that live anywhere. Most bacteria are harmless to humans, but some can cause diseases. 

Bacteria live on the skin and in the mouth, intestines, and breathing passages. They can enter the body through the natural openings such as the nose and mouth, also through breaks in the skin. If they do enter the body they can destroy healthy cells and cause infections.  Disinfectants and antiseptics can kill bacteria.

E. coli

There are a variety of E. coli bacteria present in nature. They are found in the intestines of healthy humans and healthy animals. E. coli can be spread from one person to another, this happens most often when an infected person doesn’t wash his or her hands properly.

Staph

The full name for staph is staphylococcus. There are many types of staph such as staph aureus and staph epidermidis. Staph is gram-positive spherical bacteria that occur in microscopic clusters resembling grapes.  Aureus and epidermidis are significant in their interactions with humans. Aureus colonizes mainly in the nasal passages, and epidermidis is an occupant of the skin. They can cause many infections such as food poisoning and toxic shock syndrome.  Washing your hands properly is the most important way to prevent staph.

Antibacterial and Non-antibacterial hand soaps

Regular soap decreases water’s surface tension and binds to dirt, oil and bacteria. Antibacterial hand soaps can kill more bacteria but it takes about two minutes for it the soap to start working, by then it has probably been washed off your hand. Also antibacterial hand soaps can kill bacteria that can actually benefit us. It is best if young children do not use antibacterial hand soaps because the need to interact with the germs to train their immune system. If they do not interact with some of these germs it will make them more likely to develop asthma or other immune-system diseases. 

Summary

There are many types of Bacteria. Although some are harmless, others can cause infections and diseases. Many bacteria live on your skin. That’s why washing your hands is so important. Antibacterial hand soaps are intended to kill bacteria. Knowing whether they are effective is important for people concerned about health. 
 

 

BIBLIOGRAPHY

“Bacteria.” Microsoft Encarta. 2001 edition. CD-ROM. Redmond, WA; Microsoft Corporation, 2001. 

Clark, Marie. Personal interview. December 8, 2003.

Greene, Alan. “Antibacterial hand soaps.” December 10, 2003 http://www.drgreene.com/21_819.html

Metcalf, Eric “Antibacterial Soaps, Bursting the Bubble” May 2003.

Schlessinger, David “Bacteria,” The World Book Encyclopedia, 1999. 
 

ACKNOWLEDGEMENTS

I would like to thank the following people for helping make my project possible: 
* Mr. Newkirk for helping me with my experiment.  
* Mrs. Helms for answering any questions I had.  
* My parents for transporting me to and from the hospital to do my experiment. 
* Marie Clark for helping me conduct my experiment at Memorial Hospital and supervising me. 

 


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