|
The Effect of Four Incubation
Temperatures on Three Types of Bacteria |
|
Researched by Rachel E.
|
|
The purpose of this experiment was to compare the growth rates of three types of bacteria at four incubation temperatures.
I became interested in this idea because I’ve always been fascinated with bacteria and health. I have read a lot about bacteria and their growing temperatures and I really enjoyed it so I decided to do a project on it this year.
The information gained from this experiment would help food preparers determine better temperatures to store food. It would also help hospitals, and homes know temperatures that would protect them from various bacteria.
My first hypothesis was that Staph Aureus would grow best at 37∞C.
My second hypothesis was that E. coli would grow best at 37∞C.
My third hypothesis was that the Group B Strep would grow best at 37∞C.
I base my hypotheses on a quote from Marie Clark, a microbiologist at Memorial Hospital, who stated, “These three bacteria normally grow best at 37∞ C.“ Human body temperature is about 37∞C and I thought this would be the optimal.
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
- Turbidity of each test tubes contents
The manipulated variables were the temperatures (5∞, 20∞, 37∞, and 42∞ C) and the three types of bacteria ( Staph Aureus, E coli, and G. B Strep.)
The responding variable was the growth rate of the bacteria.
To measure the responding variable I counted the number of different bacteria colonies visible to the naked eye at each temperature.
| QUANTITY | ITEM DESCRIPTION |
| 4 | Incubators |
| 12 | Plastic test tubes |
| 48 | Petri dishes |
| 1 | Sample of Staph Aureus |
| 1 | Sample of E. coli |
| 1 | Sample of G. B. Strep |
| 1 | Data sheet |
| 2 | Pair of latex or vinyl gloves |
| 1 | Fluid impermeable lab coat |
| 1 | Nephlometer (turbidity meter) |
| 2 | Micro-liter measurers (10 and 20 uLs) |
| 3 |
Bacteria spreading loops |
1. Place 12 test tubes in a tray in four rows of three.
2. Label the tubes in the front row 1, 2, 3, 4.
3. Pump 1.8ml. distilled water into the first test tube in the first row.
4. Use a cotton swab to remove some bacteria from sample containing Staph Aureus.
5. Swish the swab around in the water of the first test tube in the first row.
6. Measure and adjust the turbidity of the test tube contents on an electric density measurer so that it has 80% light transmission.
7. Remove 20 micro liters from first test tube and place it in second test tube of that same row.
8. Add 1.8 ml. to the second test tube in the first row (making a dilution of 1/10 of the first tube.)
9. Take 20 uL of solution from second test tube and put it in the third test tube of that same row.
10. Add 1.8 ml to the solution in the third test tube of that same row. This is a dilution of 1/100 of the first tube.
11. Take 20 uL of solution in the third test tube and put it in the fourth test tube of that same row.
12. Add 1.8 ml to the solution in the fourth test tube of that same row. This is a dilution of 1/1000 of the first tube. The first tube now has the most bacteria and the fourth now has the least.
13. Repeat steps 3-10 on the remaining two rows using E. coli and Group B Strep.
14. Sort 48 Petri dishes into 4 groups of 12 labeling the first 12 with the first incubation temperature.
15. Divide the 12 dishes into 3 groups of 4; label each dish in a group with one of the 3 bacteria types and the numbers 1, 2 ,3, or 4.
16. For each different incubation temperature, take another 12 and do as in steps 14 and 15 but label accordingly.
17. From the fourth test tube of row #1 (having least amount of bacteria) draw 10 uL of the diluted bacteria and place it on one Petri dish labeled with that bacteria name and the number “4”.
18. Spread bacteria evenly with a sterile loop in three directions - vertically, horizontally and diagonally.
19. Repeat steps 17-18 except use tube #3 for this bacteria and label the Petri dish accordingly.
20. Repeat step 19 except for tubes #2 and #1.
21. Repeat steps 17-20 with the other types of bacteria labeling the Petri dishes accordingly.
22. Place each of the 48 dishes in the specified incubators (12 for each incubator) for three days.
23. Take the dishes out after the time allotted.
24. Count the number of colonies grown on each dish at each temperature for each bacteria type.
25. Record the results on a data sheet.
26. After the tests have been conducted kill all of the bacteria. The bacteria laden plates and test tubes must be autoclaved.
The original purpose of this experiment was to determine the growth rates of three types of bacteria at four incubation temperatures.
The results of the experiment were that at 42∞ C. Staph Aureus grew the most overall colonies at 352 colonies; E. coli had only 320 colonies; and Group B Strep had only 64 colonies. At 37∞ C. Staph Aureus again had 604 colonies; E. coli was next at 280 colonies; and Group B Strep had 120 colonies grown. At 20∞ C. E. coli had 431 colonies, Staph Aureus had 272 colonies and GB Strep had 162 colonies. At 5∞ C. E. coli had 4 colonies, Staph Aureus had 1 colony, and GB Strep had none.
Overall the three types of bacteria grew the best at 37∞ Celsius with an average of 335 colonies grown. The next most productive temperature was 20∞ Celsius with 228 colonies. At 42∞ Celsius 245 colonies grew. The last was 5∞ Celsius that grew only 2 colonies.
From all three temperatures the bacteria that grew the most were Staph Aureus at 307 colonies. E coli was second and grew 258 colonies. Then it was Group B Strep with 86 colonies.
See my table and graphs.
My first hypothesis was Staph Aureus would grow best at 37∞C. The results indicate that this hypothesis should be accepted.
My second hypothesis was E coli would grow best at 37∞C. This hypothesis should be rejected because E coli grew the best at 20˚C.
My third hypothesis was Group B Strep would grow best at 37∞C. This hypothesis should also be rejected because GB Strep grew the best at 20˚C.
Because of the results of this experiment, I wonder if the results would change if I kept the same temperatures but saw if they grew better in a sugar or a starch environment. I also wonder if the results would have been different if I had used 32˚C or 27˚C incubation temperatures but had kept the same type of environment.
If I were to conduct this project again I would use less bacteria in the tubes so the bacteria growth would’t be as dense as it was from tubes 2, 3, and 4 (which had colonies numbering in the thousands to ten-thousands and had to be estimated as to the number of colonies grown.) As an alternative, I would then calculate the area covered by the bacteria colonies rather than count the individual colonies themselves.
| Introduction Bacteria are important to life on earth. Some bacteria are harmful to humans causing disease. Temperature can be used to control bacteria growth rates. Microbiology
Microbiology was first started by Antony van Leeuwenhoek, a Dutch lens maker, who viewed the “ wee animals “ under his microscope from rainwater and the scrapings of his teeth. Antony was known to have made 500 “microscopes” though only fewer than ten have survived to this day. In basic design the microscopes only consisted of a very powerful magnifying glass, with these Antony made some of the most important discoveries in biology, he discovered bacteria, sperm cells, blood cells, microscopic nematodes and rotifers, and much more. Bacteria
Bacteria are single celled organisms that can be harmful or not. Harmful bacteria include the bacteria that can cause Staph, Strep, Tuberculosis, Pneumonia, and Diphtheria. Bad bacteria are also the cause of anthrax in animals and soft rot in vegetables. Helpful bacteria aid the process of fermentation in making bread, yogurt, pickles, cheese, milk and butter among other things. Good bacteria also can help cure diseases; penicillin is a medicine that bacteria contributed to. Staph Aureus Staphylococcus aureus, often referred to simply as "staph" is commonly found in the nose or on the skin of healthy people. The person carrying them might get a skin infection some may not be serious like boils and pimples but some can be quite serious and can be really harmful. The leading cause of skin infections in America is Staph. E coli Escherichia coli is the formal name for E. coil. E. coli is the most studied bacterium in the history of science. Harmful strains of it live in the intestines of humans and animals. Some strains of E. coli can cause blood or urinary infections in humans. E. coli O157:H7, causes severe intestinal illness typical . Group B. Strep Group B Streptococcus or G.B. Strep infections are very rare, Group B Strep is still the leading cause of life-threatening infections among newborns, including meningitis, neonatal septicemia (bacterial bloodstream infection), and pneumonia. For women, Group B Strep can lead to urinary tract infections, womb infections, and very rarely, stillbirth. Classification Bacteria can be classified in many ways such as by their shape, their environment, and how they get their food. Environment Bacteria are found virtually everywhere. There are, however, three types of bacteria that have specific requirements for their environment in order to prosper. Aerobic bacteria need oxygen to live and thrive. Anaerobic bacteria cannot tolerate the presence of gaseous oxygen. The third type is Facultative bacteria that prefers the presence of oxygen, but can live without it. Energy Source Bacteria can also be classified by the way they get their energy or their energy source. Heterotrophs break down complex organic compounds that they get from the environment; examples of these bacteria are saprobic bacteria that can be found in decaying material, and those that rely on the process of fermentation and/or respiration. Shapes There are four shapes of bacteria, Cocci, Bacilli, Vibrato and Spruilla. Cocci are sphere shaped, Bacilli are shaped like rods, Vibrio is comma shaped, and the Sprilla is corkscrew or spiral shaped. Examples of Cocci bacteria are Micrococcus luteus. They form tetrads during regular cell division. Micrococcus species commonly have something to do with the skin. Staphylococcus species are also common on the skin. Staph Aureus can cause boils, and occasionally, more serious infections. Streptococcus species also are common but typically form chains of cells because they divide in a single plane. Streptococcus mutans commonly grows on tooth enamel and contributes to tooth decay. Examples of Bacilli shaped bacteria are Bacillus cereus, a common inhabitant of soil but also found on many food products. Bacillus species produce endospores, seen in stages of development. The cells lyse. B. cereus, causes a relatively mild food poisoning, especially on reheated fried rice in take-out food restaurants. The spores can resist destruction during cooking and can then germinate if the cooked food is not refrigerated. Two toxins are formed: one is heat-stable, produced during sporulation and causing vomiting; the other is heat-labile, produced during growth and causes diarrhea. Examples of Vibrio shaped bacteria are Vibrio alginolyticus, an agar-degrading species found in water and sea environments. The best-known species of Vibrio is V. cholera which causes cholera, a severe diarrhea disease resulting from a toxin produced by bacterial growth in the gut. Examples of Sprilla shaped bacteria are Rhodospirillum, one of the purple non-sulfur bacteria. Mostly these bacteria grow in shallow anaerobic organic-rich pools, obtaining energy from light but using organic substances such as acetate for cellular synthesis. They can also photosynthesize in anaerobic conditions, obtaining energy from light and fixing carbon dioxide into cellular materials. Rhodospirillum moves in a corkscrew motion, by waving its flagella. Colors Bacteria can have certain chlorophylls that give the bacteria natural colors like green, yellow, orange, or brown. Colonies of millions of bacteria then appear to be pink, yellowish, or light brown. A variable that controls bacterial growth is temperature. Bacteria can be grown or killed using normal or extreme temperatures. Temperature
Humans can describe the temperature
of an object by the feeling of warmth or coldness felt from contact
with it. Thermometers A thermometer is an instrument that measures the temperature of an object. A thermometer relies on the principle that a liquid changes its volume relative to the temperature of its surroundings. Liquids take up less space when they are cold and more space when they are warm. The two most important points on the temperature scale are 32F for the freezing point and 212F for its boiling point. The two types of temperature are Fahrenheit and Celsius. Fahrenheit scale-Daniel Fahrenheit decided that the freezing and boiling points of water would be separated 180 degrees, and placed the temperature of freezing water at 32 degrees. So he made a thermometer placed it in freezing water and marked the level of the mercury at on the glass as 32 degrees. Then he placed the same thermometer in boiling water and marked the level of the mercury at 212F He then put 180evenly spaced marks in between those two points on his thermometer. Celsius scale- Anders Celsius decided that the freezing and boiling points of water would be separated by 100 degrees, and he put the freezing point of water would be 100 degrees. (His scale was later changed so that the freezing point of water is at 0 and the boiling point 100.) Incubators Incubators are commonly found in labs used to keep bacteria at a certain temperature at which the organisms can live. The incubators can be set at certain temperatures and humilities that will allow the bacteria to grow at the temperature best suited to the bacteria. |
|
American Society for Microbes “Bacteria.” http://www.microbeworld.org/htm/aboutmicro/microbes/types/bacteria.htm “Antony Leeuwenhoek ” http://www.ucmp.berkeley.edu/history/leeuwenhoek.html “Bacteria,“ Microsoft Encarta. 2001. “Bacteria,” Britannica Intermediate Encyclopedia. 2002. “Bacteria Information Sheet,” http://www.newtown.k12.ct.us/~royalk/bactinfo.htm. “Bacteria Types,” http://iouwinnipeg.ca/~simmons/Chap2798/sld001.htm. Boehm, Robert E “Thermodynamics,” World Book Encyclopedia. 2001. “Cells.” Science Encyclopedia Volume Four. 1997 11/1/2004 Eddleman, Harold “What are Bacteria,” http://www.disknet.com/indiana_biolab/b003.htm. Facklam, Howard and Mary. Bacteria. 1994. 11/1/2004. 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. Marquis, Robert, Bacteria. http://encatra.msn.com/text_76154409__31/Bacteria.html. 11/5/2004. Moore, Terry, Senior Editor. “Single Celled Organisms.” The Kingfisher Science Encyclopedia. 2002. 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. Souby, Anne, Senior Editor. “Saprophytes,” Science Encyclopedia. Volume 18. 1997. “Types of Bacteria.” http://www.csc.liv.ac.uk/~ulaos/Types_of_Bacteria.htm. November 12, 2003 |
I would like to thank the following people for helping make my project possible:
- My parents for driving me to and from the hospital.
- Mr. Newkirk for correcting all of my “stuff.”
- Marie Clark for letting me use her equipment and the Microbiology lad at Memorial hospital.
- Mrs. Helms for helping with things I did not understand.
Top of page
Menu of 2004-2005 Science Projects