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The Effects of Antibiotics on Bacterial Growth

Researched by Rachel F. 
2000-01




PURPOSE

The purpose of this experiment was to determine how well various antibiotics would destroy bacteria.

I became interested in this idea when I was sick and wondered how thoroughly the antibiotic I was taking killed off bad bacteria cells. 

The information gained from this experiment would allow the medical society to know which antibiotic kills bacteria best.

 



HYPOTHESIS

My hypothesis was that the antibiotic vancomycin would kill the bacteria most  effectively.

I based my hypothesis on what lab technician Marie Clark said. She said that in her experience vancomycin has worked best for fighting off bacteria.

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EXPERIMENT DESIGN

The constants in this study were:  
   -Amount of antibiotics 
   -Temperature 
   -Time kept in incubator 
   -Number of hours bacteria has to grow 
   -Grow bacteria in same type of container  
   -Exposure to same bacteria 
   -Same kind of pads 
   -Same amount of time the pads are soaked in the antibiotic

The manipulated variable was the type of antibiotic.

The responding variable was the amount of bacteria that grows. 

To measure the responding variable I will measure the diameter of the death zone in millimeters with a caliper (ruler).

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MATERIALS 
 
QUANTITY ITEM DESCRIPTION
14 Blood Agar Plates
10 Test Tubes
20 Swabs (Q-Tips)
10  Muellar Hinton plates
70
 Antibiotic Discs
10 Inoculating Loops
30
milliliters Saline
1 Caliper
1 Colorimeter
1
 Incubator
10
  milliliters Hydrogen Peroxide
10 milliliters Gram Stain Reagense

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PROCEDURES

1. Culture the hands of ten people  (swab hands) 
2. Roll  swab on blood agar plate 
3. Streak for inoculation 
4. Incubate overnight  
5. Identify the coag negative staph 
6.  Gram stain colonies 
7.  Perform Catalase test 
a.  Put the organism on a glass slide 
b.  Put a drop of hydrogen peroxide on the glass slide where the organism is 
c.   If the organism bubbles then it's the right type of bacteria 
8.  Perform Staphaurex test 
a.  Put a drop of staphaurex solution in the circle on the staphurex board 
b.  Mix in organism with a tooth pick 
9.  Perform Sensitivity test 
a.  Dilute organism in Saline 
b.  Swab organism on plate 
c.   Apply antibiotic 
d.  Incubate over night 
10. Read sensitivity  (measure zone produced) 
11. Record and interpret the zone  
12.  Analyze the data 
13. Autoclave everything

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RESULTS

The original purpose of this experiment was to determine how well various antibiotics would destroy bacteria.

The results of the experiment were that all the antibiotics killed the bacteria very effectively. Specifically, the antibiotic cephalothin worked the best. 

See the table and graph.

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CONCLUSION

My hypothesis was that the antibiotic vancomycin would kill the bacteria most effectively.

The results indicate that this hypothesis should be rejected. The antibiotic vancomycin was the least effective antibiotic against coagulase negative staphylococcus. 

Because of the results of this experiment, I wonder if the antibiotics I used would work against a stronger type of bacteria. 

If I were to conduct this project again I would try to get a more accurate measurement of the death zones and spread the bacteria more evenly on the Mueller Hinton plates.

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RESEARCH REPORT 
  
 

INTRODUCTION 
 

     Human health is very important to our survival and happiness. However, some of the world's smallest organisms, bacteria, sometimes threaten human health. Bacteria are present everywhere.  They are present both inside and outside the human body and perform a variety of useful functions.  Some bacteria can multiply and make people sick and in some cases, bacteria illnesses can be fatal.

     Today, most bacteria-caused illnesses are treated with antibiotics.  Antibiotics are widely used all over the world.  Back in 1928 when Alexander Fleming discovered penicillin (the first antibiotic), it was called "the wonder drug."  Penicillin still is one of the most commonly used antibiotics, but unfortunately, it may be loosing its effectiveness against some diseases and infections.  There are now many different types of antibiotics in addition to penicillin.  Different antibiotics are known to fight bacteria better than others do. 
 

BACTERIA 
 

     Most people associate bacteria with illnesses and disease, but that is not quite accurate. Some form of bacteria is everywhere, on every living thing, and has been on the earth for about three and one half billion years.  In fact, it is estimated that bacteria make up a quarter pound of our body weight.  Bacteria are inside every person and animal.  They help break down food after it is swallowed and bacteria in the stomach helps digest food.  Bacteria help break down dead plants and trees, improving the soil so that it can support new life.  Bacteria are so important to humans that if bacteria weren’t present, over time, the environment would be destroyed and humans would cease to exist.

     Even though bacteria help humans in many ways, they also cause multiple sicknesses, illnesses and infections.  Bacteria cause relatively common illnesses like strep throat and minor skin infections, as well as life-threatening diseases such as meningitis and necrotising facitis ("flesh eating bacteria"). Antibiotic treatments can cure most bacterial diseases, but not all.

     Bacteria are among the world's smallest living organisms.  They come at a range of .3 to 2 microns, completely invisible to the human eye (a single micron is .001mm).  Bacteria are not only small, but after examination under a microscope, come in three main shapes.  The first shape is just plain round balls that are clumped together and are called cocci.  The second basic shape of bacteria is a rod-like shape called bacillius.  The last main shape is a spiral.  Spiral bacteria are called spirella.

     Bacteria cause disease and illness by multiplying in the human body.  In general, the faster bacteria multiply, the more severe the illness.  One of the  rarest, but fastest multiplying and most deadly bacteria is a type of streptococcus bacteria that causes necrotising fascitis ("flesh eating bacteria"). 

     Flesh eating bacterial disease isn't very common, but some people today are unlucky enough to catch it.  The disease was first described in China in 1924.  It begins with a redness on the skin at the point of infection, and then over the next few days the skin will become dusky and purplish.  Bloody blisters may form on the skin.  The patient must get medical treatment immediately.  Flesh eating bacteria multiply and kills living tissue so rapidly that a person can die in days.  Death rates are high, even with proper treatment which involves surgery (cutting away dead and infected tissue) and aggressive antibiotic therapy.  In some cases, this bacteria can eat up living tissue almost as fast as surgeons can cut it out. 
 

ANTIBIOTICS 
 

     Antibiotics have been around since about 1928.  They were first developed to cure common bacterial diseases and infections.  Early uses included curing infections of soldiers wounded in wars.  Before penicillin, one of the most common causes of death for wounded soldiers was severe infections.  Today, antibiotics are used not only to cure infections and bacterial diseases, but to make livestock healthier and grow bigger faster.

     The first antibiotic ever created was accidentally discovered in 1928 by Alexander Fleming when he noticed that bacteria didn't seem to grow around a mold that had formed on a plate or culture of bacteria.  Penicillin, named after the mold that creates it, was later manufactured and put to wide use by two British scientists named Chain and Florey.  Penicillin became known as the "wonder drug" for saving so many lives.  It was effective against many bacterial diseases.

     However, penicillin is not as effective as it used to be. Many antibiotics that once cured bacterial diseases no longer work as well.  Bacteria is somehow finding a way to protect itself from antibiotics.  Scientists guess that antibiotics kill most bacteria, but some bacteria survive.  Over time, the antibiotic resistant bacteria multiply until they can no longer be controlled or killed with common antibiotics.  Bacteria may be adapting and evolving faster than scientists can develop new, stronger antibiotics.

     Penicillin is just one of many antibiotics.  Erythromycin is often used as a substitute for penicillin.  It is effective in killing many of the same bacteria that penicillin does.  It cures gram positive cocci and streptococcal and pneumococcal infections.  Erythromycin doesn't have the history of penicillin, but it has proven itself to work twice as well.

     Ampicillin is another antibiotic that is related to penicillin, but is more commonly use and may be even more effective.  Ampicillin cures blood poisoning and urinary tract infections as well as some gram negative bacterial infections such as meningitis. 

     One relatively new antibiotic is vancomycin.  Vancomycin is regarded as one of the most powerful antibiotics, killing bacteria when other antibiotics don't work.  In fact, today many hospitals restrict vancomycin's use because they are afraid that bacteria will adapt and make it less effective.  In some cases, vancomycin can only be used with the Infectious Disease Unit's permission.  These are only a few of the most common antibiotics.  Doctors and scientists are extremely concerned that many of these common antibiotics are losing their effectiveness. 
 

VIRUSES V. BACTERIA 
 

     Like bacteria, viruses are disease causing organisms.  However, antibiotics are not effective against illnesses caused by viruses.  Viral infections and disease generally have to run their course and will gradually go away.  The only method to stop viral illnesses is by creating vaccines and through immunization.

     Viruses are found inside humans, animals, plants, fungi and bacteria.  Viruses are made of either DNA or RNA.  Viruses are about 20 to 100 times smaller than bacteria.  Viruses vary from 30 nanometers to 450 nanometers.  Viruses are often called a free-living cell because they cannot reproduce outside of a living cell.  As they multiply, viruses either damage or kill the living cells they infect. 
  
 

ANTIBIOTIC RESISTANT BACTERIA 
 

     One huge problem in the antibiotic field today is that bacteria are becoming resistant to antibiotics. Scientists don’t exactly know why bacteria are becoming resistant to antibiotics, but they think that antibiotic use for animals could be one reason. A lot of ranchers and farmers put antibiotics in their animals’ food. This helps the animals grow bigger faster and helps their cattle or sheep stay healthier. This may be a good thing for farmers, but not for society. About an average of thirty-five percent of all the antibiotics produced are fed to animals and this amount could be as high as seventy percent. The more antibiotics are used in our daily lives, the greater the chance of the survival and adaptation of resistant strains of bacteria. Antibiotics that once worked to fight disease may no longer work.  
     Another possible reason for antibiotic resistance could be that humans overuse and misuse antibiotics. When people take an overdose of antibiotics, this just gives the bacteria more of a chance of becoming resistant to an antibiotic. In fact, resistance is becoming such a problem that scientists can’t come up with new antibiotics fast enough to replace old, less effective ones. If this keeps up over time, there just might be no more antibiotics that are of use to humans. Another common misuse of antibiotics is trying to treat a viral infection. Antibiotics can’t cure viruses and this only makes the bacteria in the body stronger. Resistant bacteria can pass through people so quickly that they wouldn’t even know it.  
 

     This is why humans should avoid the misuse of antibiotics. If humans even lowered their use of antibiotics by thirty percent, bacteria would have a less chance of becoming resistant to antibiotics. In the past few years discoveries of new, effective antibiotics have been decreasing. If humans aren’t careful in the future their existence could be threatened due to antibiotic resistant bacteria.  
  
  
  
  
 

SUMMARY  
 

Bacteria play a big roll in everyone’s life. They provide many beneficial uses in humans and in nature, but also can be very harmful. Bacteria adapt and change to be more resistant to antibiotics, making antibiotics less effective to maintain the health of the human population. Effective antibiotics are slowly becoming scarce and are more important now than they have ever been. If antibiotic use is not controlled, which means cutting down their overuse and misuse and even limiting the amount of antibiotics we feed animals, bacteria caused disease , infections and illness could once again be a very serious threat to human health.

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BIBLIOGRAPHY 
  
 

"Antibiotic resistance", [Online] Available at http://www.doh.gov.uk/antibioticresistance/antibiotics2.htm

"Antibiotics", [Online] Available at http://encarta.msn.com/find/concise.asp?ti=761577894&sid=12

Facklam, Howard and Margery. Bacteria. New York: Twenty ?First Century Books, 1994. Pp. 22-24, 8-9, 7-8

Marquis, Robert.  "Bacteria," The World Book Encyclopedia, 1999.  
Pp. 19, 21-22

"Microbiology", [Online] Available at http://www.ha.org.hk.qmh/micro/ewelcome.html

" Penicillin", [Online} Available at http://helios.bto.ed.ac.uk/bto/microbes/penicill.htm

Sladeck, N.E.  "Antibiotics," The World Book Encyclopedia, 1999. Pp. 352-353

"Streptococcal Disease", [Online] Available at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/groupastreptococcal_g.html

"Vancomycin", [Online] Available at  http://home.eznet.net/~webtentvanco.html 

"Virus", [Online] Available at http://esg-www.mit.edu:8001/esgbio/cb/virus.html

"Virus", [Online] Available at http://encarta.msn.com/index/conciseindex/5E05EE5000.htmz=1&pg=2&br=1

"Virus Replication", [Online] Available at http://esg-www.mit.edu:8001/esgbio/cb/virus/phagereplication.hrml  
 

ACKNOWLEGMENTS

       I would like to thank the following people for their help with my science project:

            -Marie Clark for making my project possible.

            -The SRC commitee for allowing me to do my project.  
  
  
  
  
 

 


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