| The Effect of Temperature on Bacteria Growth Rate | |
Researched by Rachel E.
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The purpose of this experiment was to determine the effect of incubation temperature on bacteria growth rate.
I became interested in this idea because I’ve always been fascinated with bacteria and health.
The information gained from this experiment will help society know at what temperature bacteria normally grow, and that knowledge will help determine what temperatures to set appliances like heaters in institutional kitchens, restaurants, and homes.
HYPOTHESIS
My hypothesis was that bacteria will grow best at 37° C because it very close to body temperature.
I based my hypothesis on The Science Encyclopedia Volume 2 that states, “Bacteria grow best between 10* and 40* C” any temperature outside that range will cause most bacteria to die.
The constants in this study were:
- Testing procedures
- Incubator, incubator temperature, and humidity
- Equipment type
- Magnifying glass used to view colonies
- Time exposed to the specific temperature
- Light
- Density of the test tubes
- Species of my bacteria
The manipulated variable was the temperature of the incubator.
The responding variable was the number of live colonies after their incubation time.
To measure the responding variable I will count the number of colonies visible to the unaided and aided eye.
| QUANTITY | ITEM DESCRIPTION |
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Plastic test tubes |
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Petri dishes |
| My bacteria | |
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Moist plastic bag |
| Broth that supports the bacteria growth | |
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Data sheet |
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Pair of latex or vinyl gloves |
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Fluid impermeable lab coat |
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Nephlometer |
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Micro liter measurers (10 and 20 uLs) |
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Density measurer |
Procedures
Gather Bacteria:
1) Take two Petri dishes and remove the lids
2) Set one of the dishes in a kitchen and one in bedroom
3) Let them collect bacteria for one hour
4) After an hour place the lids on the dishes
5) Place the dishes in a moist plastic bag and seal
6) Take to a hospital and have them analyze the bacteria and place
each collected sample in a separate prepared broth that supports their
growth
7) Let the bacteria grow enough so that you can work with it for your
experiment
8) Divide the two cultures of bacteria into 2 tubes each and add more
broth
9) Label those tubes 1-4
Conduct Temperature Trials:
10) Place 12 test tubes on a tray in 4 rows of 3.
11) Label the first tube in each row 1, 2, 3, 4.
12) Pump 1. 8 ml. distilled water into the first test tube in the 1st
row
13) Take a cotton swab and remove some bacteria out of the #1 sample
of bacteria.
14) Swish the swab around in the water of the first test tube in the
1st row
15) Measure and adjust turbidity of test tube contents on an electronic
density measurer so that it has 80% light transmission.
16) Take 20 micro liters (uL) of the solution in the first test tube
in the 1st row and place it in the second test tube of that same row
17) Add 1. 8 ml. distilled water to the second test tube.
18) Take 20 microliters (uL) of the solution in the second test tube
in the 1st row and place it in the third test tube of that same row
19) Add 1. 8 ml. distilled water to the third test tube.
20) Repeat steps 12-19 to the remaining 3 rows, except use only the
respective bacteria for that row (for example, bacteria sample #3 is only
used for test tubes in row #3)
21) Sort 16 sterile Petri dishes into groups of 4 and label each group
with a number, 1-4. Within each group additionally label each dish
with one of four temperatures to be tested: 42 C. , 37 C. , 20 C. , 5 C.
22) From the third test tube of row #1 draw 10 uL of the diluted bacteria
and place into a Petri dish labeled #1. Do this four times total,
once for each temperature group: 42, 37, 20, 5.
23) Spread the bacteria around the plate in 3 directions (vertically,
horizontally, and diagonally) with a plastic loop.
24) Repeat steps 22 and 23 with the diluted bacteria from the
other 3 rows being sure to place bacteria in the respectively numbered
Petri dishes.
25) Place the Petri dishes in the four incubators at the temperatures
specified on each dish.
26) Leave them in the incubator for 6 days
27) Take the Perti dishes out immediately after that time
28) Count the live bacteria colonies with the use of a magnifying glass
(if necessary) or the unaided eye.
29) Record the number on a data sheet
30) After all the bacteria tests have been done kill all the bacteria
you have worked with. They must be autoclaved.
The original purpose of this experiment was to determine the effect of incubation temperature on bacteria growth rate.
The results of the experiment were that the bacteria grew the best at 20°C and 37°C with the average of 36. 75 colonies. The second group of 42°C had the average of 2. 25 colonies. The group of 5°C had no colonies grown so the average was 0.
See the table and graph below.
My hypothesis was that bacteria would grow best at 37° C.
The results indicate that this hypothesis should be rejected. Although 37° C was one of the two highest, it was tied with 20°C having an average colony count of 36. 75.
Because of the results of this experiment, I wonder if the results would be similar if I used bakers yeast and exposed it to the same temperatures. I also wonder how other temperatures might have affected the results, especially 32° C and 27° C.
If I were to conduct this project again I would determine the area on the Petri dish covered by colonies, rather than counting the colonies. All colonies, regardless of size, were counted equally in the current experiment. That might not be the best way to determine growth. Another thing that I would do differently is incubate more plates at each temperature so that the results would be more meaningful.
| RESEARCH REPORT
Intro Bacteria are important to life on earth. Some bacteria are harmful to humans causing disease. Temperature can be used to control bacteria growth. Bacteria Bacteria are single celled microscopic organisms. Bacteria can help or destroy animals, plants, and humans. Bad bacteria
can cause strep, staph, pneumonia, diphtheria, and tuberculosis in humans.
Bacteria are also the cause of anthrax in animals and soft rot in vegetables.
Some bacteria have natural colors. Certain species contain chlorophylls that make them appear green, orange, yellow, and brown. Color pictures of bacteria normally seen on the Internet or in books have been enhanced. Large bacteria colonies of millions of bacteria may appear pink, yellowish, or white. Bacteriologist Christian Gram invented gram stain in 1844. Gram stain classifies bacteria into two groups; gram positive and gram negative. Gram positive accepts the violet iodine stain, and gram negative resists the stain. Bacteria get nutrients from almost anything. They get nutrients
from gasses like sulfur and can make their own food via photosynthesis.
Parasitic bacteria hook onto other cells and feed through them. The bacterium
being fed through is called the host; and the bacterium feeding sometimes
harms the host.
Bacteria can range in size from bacteria you can see with the unaided eye to bacteria that are so small that they were once thought to be viruses. Bacteria can live almost anywhere. They can live in the air, water, soil, and even in the human body. The bacteria in the intestines help you keep healthy. Bacteria divide by simple fission. They make a clone of themselves inside their cell then they split in the middle. Then they can form chains, cubes or just stay alone. Bacteria have three distinct shapes, bacilli that are rods, cocci that are spherical, and spirilla that are spirals. Diplo is when two bacteria cells link together, strepto is when bacteria cells form chains, and staphlyo is when they form clusters. Bacteria cells have an outer capsule around the cell wall that is sticky. This capsule protects the cell but also allows it to stick to other cells. Some bacteria move with flagella that move in a circular motion that propels the cell along, but spirilla moves in a corkscrew motion. There are three types of bacteria, aerobic that must live in the presence of oxygen or the cell will die, anaerobic that cannot live in oxygen, and the third type is facultative aerobes that prefers oxygen but can live with out it. Temperature Temperature is the measurement of heat energy in a substance, measured mainly by a thermometer, often in degrees Fahrenheit or Celsius Thermometers measure temperature often in Fahrenheit or Celsius by using a graduated glass tube with mercury or colored alcohol that contracts or expands according to the rate of temperature change. Thermodynamics is the study of various forms of energy such as heat
and conversion of energy from one form to another.
Summary Temperature helps control bacteria life and death. Temperatures that are too hot or too cold will kill some or all bacteria. Bacteria can help with illnesses and create them. Bacteria can also help with the process and making of foods. |
| BIBLIOGRAPHY
American Society for Microbes “Bacteria” http://www. microbeworld. org/htm/aboutmicro/microbes/types/bacteria.htm. “Bacteria Types” http://iouwinnipeg. ca/~simmons/Chap2798/sld001.htm. “Bacteria” Microsoft Encarta, 2001. “Bacteria” Britannica Intermediate Encyclopedia, 2002. “Bacteria Information Sheet” http://www. newtown. k12. ct. us/~royalk/bactinfo.htm. Boehm, Robert E. “Thermodynamics” World Book Encyclopedia 2001. Eddleman, Harold “What are Bacteria” http://www. disknet. com/indiana_biolab/b003.htm. Hillard, Kate “The Kingdoms of Archaebacteria and Eubacteria” http://co. essortment. com/archaebacteriae_rmkr.htm. “Kingdom of Monera” http://fig. cox. miami. edu/Faculty/Dana/monera.html. November 12,2003. McKeever, Susan Senior, Editor, “Bacteria” Encyclopedia of Science 2001. Past, Louis and Koch, Robert “Bacteria” World Book Encyclopedia, 2002. Schlessinger, David “ Bacteria” World book Encyclopedia, 2002. , Moore, Terry. Senior Editor “Single Celled Organisms” The Kingfisher Science. Encyclopedia 2002 Souby, Anne, Senior Editor “Saprophytes” Science Encyclopedia Volume 18 1997. “Types of Bacteria” http://www. csc. liv. ac. uk/~ulaos/Types_of_Bacteria.htm.
Wit, Lawrence C. “Amoeba “World Book Encyclopedia, 2002. |
I would like to thank the following people for helping make my project possible:
- My parents for driving me to the hospital.
- Marie Clark for helping me with my experiment.
- Mr. Newkirk for correcting all of my stuff.
- Mrs. Helms for helping me with problems.
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