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The Effect of Heating vs Freezing on The
Survival Rate of Bacteria |
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Researched by The purpose of this experiment was to determine which heating or freezing temperature is a better method to kill bacteria.
I became interested in this idea when I froze bacteria at extreme temperatures last year and wondered whether heating or freezing would kill more bacteria because freezing bacteria was a very effective way to either slow down the growth rate or kill bacteria at extreme temperatures such as –60∞C.
The information gained from this experiment could help scientists and doctors understand how freezing or heating bacteria can be helpful.
My first hypothesis was that the highest heating temperature would kill more bacteria than lower heating temperatures.
My second hypothesis was that the lowest freezing temperature would kill more bacteria of each type than less extreme freezing temperatures.
I based my second hypothesis on the results of my experiment from last year, although I tested only Staph and E. coli.
The constants in this study were:
∑ The testing procedure
∑ The time the bacteria was frozen and heated
∑ The amount of bacteria
∑ The way they were measured after freezing and heating
∑ The four types of bacteria
∑ The vials the bacteria were in
∑ The temperatures of the refrigerators were always –20°, -30°, and -60° Celsius
∑ The heating temperatures were always 5°, 35°, and 40° Celsius
The manipulated variable was the freezing and heating temperatures during storage.
The responding variable was the survival rate.
To measure the responding variable, I counted the bacteria colonies.
| QUANTITY | ITEM DESCRIPTION |
| 20 micro liters | Escherichia Coli |
| 20 micro liters | Staphylococcus Aureus |
| 20 micro liters | Pseudomonas Aeruginosa |
| 20 micro liters | Straptococcus Agalactiae |
| Lots |
Cotton Swabs |
| Lots |
Disposable Pipette Tips |
| Lots |
Sterile Saline solution |
| 120 | Test Tubes |
| 120 |
Blood Agar Plates |
| 120 |
Inoculating Loops |
| 1
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10 Micro liter Pipette |
| 1 |
200 Micro liter Pipette |
| 1 |
Colorimeter (turbidity meter) |
| 1 |
Lab Coat |
1. On day 0, obtain the following bacteria from hospital lab.
- Escherichia Coli
- Staphylococcus Aureus
- Pseudomonas Aeruginosa
- Streptococcus Agalactiae
3. Divide one solution of bacteria between 30 vials, with 200 micro-liters per vial.
4. Select five of these vials and label them with the name of the bacteria, the temperature of storage, and the vial number. This is an example for Staphylococcus Aureus at 35° C.: SAU V.1 35°, SAU V.2 35°, SAU V.3 35°, SAU V.4 35°, SAU V.5 35°
5. Repeat steps 3-4 with all the bacteria and all temperatures.
6. Store bacteria labeled 5°, 35°, and 40° at those Celsius temperatures.
7. Store bacteria labeled –60°, -30°, and –20° C. at those temperatures.
8. On day one, take all vials marked “V.1” out and let them sit for 10 min. at room temperatures.
9. Refreeze or reheat all these vials where they belong.
10. On day two take out all V.1 and V.2 vials, and let them sit for 10 min. at room temperature.
11. Refreeze or reheat all these vials where they belong.
12. Repeat steps 8-9 for three more days and additionally removing V.3 on the third day, V.4 on the fourth, and finally V.5 on the last day.
13. On day 6, pipette 10 micro-liters from each vial to its own blood agar plate.
14. Spread the bacteria with inoculating loop over the surface of the blood agar plate. Label plates exactly as the vials were labeled.
15. Incubate bacteria overnight at 37° Celsius.
16. Remove plates from incubator.
17. Do a colony count for each plate under fluorescent light using the unaided eye. Record this number.
18. Destroy all bacteria on equipment contaminated with bacteria in autoclave-using hospital’s procedures.
The original purpose of this experiment was to determine whether heating or freezing is a better method to kill bacteria.
The results of the experiment were that the bacteria that was frozen had way more bacteria than the ones put in 35∞ and 40∞ heaters.
See my tables and graphs.
My first hypothesis was that the highest heating temperature would kill more bacteria than lower heating temperatures.
My second hypothesis was that the lowest freezing temperature would kill more bacteria of each type than less extreme freezing temperatures.
The results indicate that both hypothesis should be should be accepted.
Because of the results of this experiment, I wonder if time affects the number of bacteria.
If I were to conduct this project again I would freeze and heat the bacteria longer than five days.
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Bacteria
Bacteria are one-celled organisms that exist almost everywhere. They
exist in water, soil, air, even the human body. There are bacteria
inside you, there are bacteria around you. Bacteria are so small, they
measure about 0. 3 to 2. 0 microns (1 Micron=0. 001 millimeter. )
Scientist classify bacteria as prokaryotes. Some bacteria are
scrounging which means parasitic. They cause diseases by producing
poisons called toxins. Others are either harmless or even helpful.
There are many types of bacteria. Here are a few examples of commonly
known bacteria. Cocci, are round looking bacteria, Bacilli, which are
rod shaped bacteria, Vibrios, which look like bent rods, and Spirilla,
are like spiral- shaped bacteria.Eschericha Coli
E. coli is the abbreviated name of the bacterium in the Family
Enterobacteriaceae named Escherichia coli. “Approximately 0.1% of the
total bacteria within an adult's intestines (on a Western diet) is
represented by E. coli.” The name Escherichia comes from the name of
the person called Escherich, who in 1885 first isolated and
characterized this bacterium. There is also a special type of bacteria
called Eschericha Coli 0157:H7. Eschericha coli O157:H7 is one of
hundreds of strains of the bacterium Escherichia coli. Although most
strains of Eschericha Coli are harmless and live in the intestines of
healthy humans and animals. But Eschericha Coli 0157:H7 can also
produce a powerful toxin and can cause severe illness. If one eats
uncooked meat or unpasteurized milk, it can cause stuff such as bloody
diarrhea.Staphylococcus Aureus
Staphylococcus aureus, often called staph, are bacteria commonly
carried on the skin or in the nose of healthy people. Once in a while,
staph can cause an infection; staph bacteria are one of the most common
causes of skin infections in the United States. Most of these
infections are minor and most can be treated without antibiotics.
However, staph bacteria can also cause serious infections. “In the
past, most serious staph bacteria infections were treated with a
certain type of antibiotic related to penicillin.” Over the past 50
years, treatment of these infections has become more difficult because
staph bacteria have become resistant to various antibiotics.Pseudomonas Aeruginosa
Pseudomonas aeruginosa is an aerobic rod belonging to the bacterial
family Pseudomonadaceae. “The family includes other genera, which,
together with certain other organisms, constitute the bacteria
informally known as pseudomonads.” These bacteria are common
inhabitants of soil and water. They occur regularly on the surfaces of
plants and occasionally on the surfaces of animals. Streptococcus Agalactiae
Streptococcus agalactiae is a bacterium colonizing the intestinal area
of an important proportion of the human population. However, it is also
a pathogen, which is the leading cause of invasive infections in
neonates and causes septicaemia, meningitis and pneumonia. “Fifty-five
per cent of the predicted genes have an ortholog in the Streptococcus
pyogenes genome, representing a conserved backbone between these two
streptococci.” Heat
The heat of an object is the total kinetic energy of its molecules,
while the temperature of the object is the measurement of the average
energy of its molecules. “The Molecular Theory of Matter gives an
explanation of heat and temperature.” Specific heat is a way to
compare heat from different materials. Heat energy can cause expansion
in many materials. Humans need heat for many reasons, such as cooking
food and use it to warm up. Heat of an object is the total kinetic
energy of its molecules. The Molecular Theory of Matter shows when
molecules have more energy, they move faster. Specific heat is a
way
to compare heat from different materials. Heat can cause expansion in
many materials.Freezing
The freezing point of something is the temperature at which a substance
changes from a liquid to a solid. The freezing points of different
substances vary depending on what it is. The freezing point of water is
around 32˚F. However the freezing point of mercury freezes at –38.87∞C.
The freezing point of any substance depends on the pressure pushing
against it. The freezing point of most liquids can be lowered by adding
another substance. A great increase of pressure can affect the freezing
point of substances such as antimony, bismuth, and water. |
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“Bacteria,” Britannica Intermediate Encyclopedia, 2002. “Bacteria,” ENCARTA Encyclopedia Deluxe, 2001. Clark, Marie. Personal Interview. December 5, 2004 Chesick, John P. “Freezing Point,” World Book Encyclopedia, 1998 Marquis, Robert E. “Bacteria,” November 18, 2004 http://www.encarta.msn.com Schlessinger, David. “Bacteria,” World Book Encyclopedia, 2002. |
I would like to thank the following people for helping make my project possible:
- My parents for giving me ideas and driving me to Memorial Hospital.
- Mr. Newkirk for helping me correct my report and for taking time after school to help me with this project.
- Marie Clark for helping me conduct my experiment considering how large my sampling was and the materials involved.
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