Jon+L.

== == = = =The Effect of Temperature on Bacterial Growth=

The human body is a fascinating machine. Yet scientists are puzzled over the raise in body temperature known as “fever.” Various medications have been prescribed to lower such a fever, but there is still debate about what fever actually does. Some debate that it is only a symptom, and advocate the prescription of medicine that lowers the fever. Others argue that fever is a way to help fight off infectious diseases, by raising the body temperature high enough for invading bacteria to be killed after a while. This investigation closely looks at the claim that fever hinders bacteria, as well as looks into the comparison between bacteria growing at different temperatures. The goal of this experiment is to find out what temperature does to the growth of bacteria by monitoring the number of bacteria colonies that appear while adjusting only the temperature. I expect the dish of bacteria placed in the incubator at 34 degrees to have the most bacteria colonies, while the dish at room temperature and the dish in the second incubator set at 38.5 degrees to have less bacteria colonies, and the dish in the refrigerator to not grow bacteria at all. The dish at 34 degrees most represents normal body temperature, and should have a significant amount of bacteria, while the dish at 38.5 represents fever temperature and should have fewer bacteria.

Question(s) for investigation:

How does temperature affect bacteria growth?

Independent variable and how it will be measured:

Temperature, observed by thermometer or set by temperature dial on incubator.

Dependent variable(s) and how it (they) will be measured:

Growth, observed by counting bacterial colonies.

Variables held constant:

Amount of bacteria to start with, type of bacteria

List of the materials and Sketch of the Setup:

4 Petri dishes with agar (sterile) Cotton swabs (sterile) Hand lens, if needed Access to incubator Access to a drawer where the bacteria sample will not be disturbed (room temperature) Access to a refrigerator Access to a second incubator, set to 38.5 degrees. Access to laptop surfaces, namely the finger-pad. (bacteria source)

Who else will work on this investigation? Who will be responsible for collecting the materials to get started and when will all materials be ready to begin?

I will be working alone on this investigation, and I will gather the resources needed to start.

Procedure/Method:


 * WARNING: Although the bacteria should be harmless, there is a possibility that the bacteria grown can be harmful to humans. Therefore, practice caution if the dish breaks open.**

1. Use cotton swabs to pick up bacteria from the mouse pad and wipe it onto each of the agar layers. 2. Tape all the Petri dishes shut, then label each one based on where the bacteria is going to be stored. 3. Place the dishes in the designated places, one in the refrigerator, one in a drawer, on in the incubator, and on in another incubator where the temperature is set to 38.5 degrees. 4. When finished, you should have done what the sketch shows (wipe bacteria on agar plates, put one plate in each location) 5. Record the approximate time each dish was placed in its place. 6. During the next class period, calculate the amount of time the bacteria have been given to grow. 7. Remove each Petri dish and count the number of colonies in each dish. Record in data table. 8. Replace each Petri dish in its designated place. 9. Repeat 5-7 for the next available class periods.

Data:

What other data do you expect to include in a report of your results?

I will also include a graph as a visual representation of my data, otherwise nothing else.

Expectations: What do you think might happen and why?

I think there will be more colonies in the dish placed at 37 degrees Celsius, while there will be fewer colonies in the other dishes. This will explain why bacteria can live and invade a healthy human and its cells, and why fever helps to kill the bacteria. (see below for more expectations)

What other results do you imagine might happen and what would they mean?

The dish that was warmer than 37 degrees might have more bacteria, showing that there is a certain type of bacteria that could survive the unusual temperatures. The same idea would be true if there were more bacteria in the dish inside the refrigerator.

Communication: How will you plan to communicate your work clearly to others?

I will provide a data table with observations made during the experiment, explain the data, then hypothesize on the data and guess how this applies to real life.

What do you expect to accomplish in EACH of the next three class periods in which you can work on this investigation?

The first class period would only be preparing the dishes and then placing them in their designated places. The next two would be devoted to counting the number of colonies that appear on the dish. Note: (do not erase this) Bacteria prepared at about 12 noon on Friday the 27th, bacteria from finger-mouse pad on laptop. Also: Second batch of bacteria prepared at about 2 in the afternoon on Wednesday the 9th of May.

Expectations:

The dish at the highest temperature should not have many bacteria colonies. This is because in sterilization, bacteria are killed from exposure to high temperatures for a long period of time. Some of the more resiliant bacteria may survive, so there should be a few colonies on the dish there.

The dish placed in the incubator set at 34 degrees should have the most colonies. This is because it closely resembles body temperature, a moist and warm environment, where bacteria can grow fast. Sterilization and fever raises this temperature a few degrees higher, which kills the bacteria.

The dish in the refrigerator should not have any bacteria on it, as the environment is way too cold for them to grow.

(number of colonies) || after 146 hours: || after 240 hours: || after 290 hours: || after 336 hours: || after 434 hours: || after 480 hours: || after 576 hours: ||  ||   || (previous colony seems to have disappeared) ||  ||   ||
 * First batch
 * Refrigerator || 0 || 0 || 0 || 0 || 0 || 0 || 0 ||  ||   ||
 * Drawer || 3 || 3 + mold || 3 + more mold || 3 + mold + small dots || 3 + mold + small dots || 3 + mold + many dots || 2 + mold+ many small dots (dots appearing in mold colonies)
 * Incubator || 35 || 38 || 34 || 36 (faded and dried) || 37 (faded) || 34 (faded) || 26 (faded,some barely visible) ||  ||   ||
 * Incubator 2 || 13 || 14 || 13 || 14 || 13 || 13 || 10 ||  ||   ||

(number of colonies) || after 46 hours: || after 144 hours: || after 190 hours: || after 286 hours: ||  ||   ||   ||   ||   || (need new standard of measurement) || 1000+ small, 3 larger || 1000+ small, 4 large || 1000+ small, 4 large ||  ||   ||   ||   ||   || (patterns forming) ||  ||   ||   ||   ||   ||
 * Second batch
 * Refrigerator || 0 || 0 || 0 || 0 ||  ||   ||   ||   ||   ||
 * Drawer || 1000+ tiny colonies
 * Incubator || 1 || 4 || 5 || 5 (faded) ||  ||   ||   ||   ||   ||
 * Incubator 2 || 50 small colonies || 50+ small, 9 large || 50+ small, 13 somewhat larger || 50+ small, 7 larger

Other Observations: In the first batch of bacteria, the dish in the drawer apparently hosted a mold infestation. My most likely guess is that when the lid was closed, spores were trapped inside the dish, which grew later. One of the mold clumps also seemed to engulf a small bacteria colony.

In the dishes in the incubators, the agar surface seems to have what look like fine lines, sprouting from a point and expanding in all directions. This is usually noted when the agar layer itself is very thin. and the bacteria themselves are fading away, sometimes cracking on the agar surface.

Many small dots that look like smaller bacteria colonies appeared on the second batch of bacteria, especially in the dish in the drawer where there appeared to be 1000+ of these colonies. For now, I will count that as separate and will only count the significantly larger, colored dots that appear on the plates.

See the zip file above to see pictures of the bacteria.

In both batches (excluding any small bacteria colonies) the order of which dish had the most bacteria remained the same. In all batches from most to least bacteria colonies, the dish in the incubator at 34 degrees Celsius had the most, followed by the one in room temperature, the one in the incubator set at 38.5 degrees Celsius, and the refrigerator. This means that for the bacteria, (approximately) 34 degrees is the optimal temperature for bacteria growth, while the refrigerator (near 0 degrees) was the worst temperature for growth. 38.5 degrees Celsius was not an optimal temperature, either, as there were less colonies in there than in the incubator at 34 degrees.

Both batches of bacteria seemed to have different amounts of bacteria colonies. In the first batch, there were many colonies on the incubator dish, and the number of the colonies on the other dishes seemed to fit the other numbers. In the first batch of bacteria, there seemed to be no bacteria in the refrigerator, some bacteria in the drawer, much more bacteria in the incubator at 34 degrees, and fewer bacteria in the other, set at 38.5 degrees. The numbers, in relation to each other, made sense. However, in comparing the two dishes from the incubator at 34 degrees, the number of colonies in both dishes is found to be significantly different. In this specific dish, there were significantly more bacteria in the first batch than in the second. This is most likely due to the fact that I took bacteria from different laptop mouse-pads, and also because I may not have rubbed the cotton swab as much on either pad. Whatever the cause, it is clear that I must compare the numbers to others in the same batch, not from a different batch. The first batch of bacteria was (unfortunately) prepared at the start of a vacation, therefore there were no measurements taken before 146 hours. As a modification, it is advised that the first batch of bacteria be prepared and watched within 146 hours, to monitor the bacteria growth. After 146 hours, it seems that new bacteria colonies do not appear. As time passed it seems that the bacteria in the incubators used up the nutrients in the agar faster than the other two. This means that bacteria growth will stop at a certain time for those two locations, while in the other two locations, there is still enough agar to sustain the bacteria longer. The bacteria seemed to absorb nutrients from the agar faster than the bacteria not in the incubators. It appears that at higher temperatures, bacteria will absorb nutrients faster. If there is a follow-up experiment, thicker agar layers are needed so that the time the bacteria will all grow at the same time will be longer. I have noticed that bacteria colonies are not just one specific color and size. Apparently, as you can see in the pictures, one dish had about a thousand small bacteria colonies. According to the original procedure, I have to count all the little dots and record them down. In this case, it is too time-consuming to count all the dots. This means that another standard of measurement has to be used, and for this experiment, I have decided to ignore the small colonies and only count the bigger ones, although this method is more like purposefully ignoring a section of the data, so the method needs to be revised. Even though this experiment revealed that temperature has an impact on bacterial growth, it still raises many more questions. For instance, does temperature affect the rate that bacteria are absorbing nutrients from the agar? Although this idea has been tried for four temperatures and they all hold true, it is still not enough to confirm this idea. If this is true, perhaps it is better to lower fevers in order to prevent bacteria from absorbing too many nutrients from the body. And, what else affects bacteria growth? Differences in environment may have something to do with bacteria growth. Instead of placing the dishes in different temperatures, perhaps a good experiment will involve exposing the dishes to different radiation at the same temperature.

Appendix:

The Petri dishes are lined with agar.
 * Agar**: Nutrient-rich substance that the bacteria can grow on. It is derived from seaweed. (From Malay word “Agar-Agar”)

It is claimed that atoms cannot be divided further, but it has been proven wrong.
 * Atom**: The smallest common unit that makes up both living and nonliving things. They always vibrate, but speed varies at different temperatures (unless, theoretically, at absolute zero, where atoms do not move.). This is not to be confused with cell, which is the smallest common unit that makes up all living things. (From Greek “atomos”, meaning “undivided”)

These bacteria are dangerous, and therefore you should leave before you get sick.
 * Bacteria**: Unicellular prokaryotes that live in colonies. Reproduces at different rates at different temperatures, but multiply best at about 34 degrees Celsius. It can grow on agar. (From Greek //βακτηριον////, meaning “small stick”)//

The patient's body temperature has risen to 38.5 degrees.
 * Body Temperature**: Temperature of the body’s blood at any given time. If the body has been invaded by pathogens, the body temperature may go up (see fever).

Cells undergo mitosis.
 * Cell**: The smallest unit of all living things. There are two types: eukaryotic and prokaryotic. Eukaryotic cells have a nucleus, while prokaryotic cells do not. Bacteria are prokaryotes. (Named after rooms in old monasteries which were called “cells”)

The Celsius scale is much easier to use everyday than the Fahrenheit scale.
 * Celsius**: A unit of measure for temperature, with the freezing point of water as 0 degrees, and the boiling point of water at 100 degrees. (Named after the man Anders Celsius, who created the scale.)

Bacteria colonies are now appearing day after day on the dish.
 * Colonies**: Groups of bacteria living together. They appear as a dot on agar plates. (From Latin //colōnia ,// “settler”)

The question of what fever does for the body is still highly debated.
 * Fever**: The human response to some infectious pathogens. It involves raising the body temperature to kill off the pathogens. (From Latin )

Mushrooms are a type of fungus.
 * Fungus**: (plural: “fungi”) A group of eukaryotes that feed from surrounding dead plant and animal matter. Molds are a type of fungi. (From Latin “fungus” meaning “mushroom”)

Bacteria growth today seems to become more and more rapid as time passes.
 * Growth**: The progression of something becoming more complex. In the terms of bacterial colonies, growth is measured by its expansion. (From Old English “grōwan”)

Heat does not have mass.
 * Heat**: A form of energy, related to temperature in that it excites the atoms that heat comes in contact with. (From Old English “hǣtu”)

Incubators are used for warming eggs until they hatch, as well as growing antibiotic-resistant bacteria and mold.
 * Incubator**: A machine that raises the temperature inside to a certain degree, where it can be used to grow microorganisms. (means “to lie down in something” in late Latin)


 * Mold**: A type of fungus, it reproduces using spores. It can grow on agar. (From Middle English $)$Mold also grows on wet bread in room temperature.

This particular nutrient will cause death if too much is taken.
 * Nutrient**: "A chemical substance that an organism needs to survive." (from textbook) (From Latin //nūtrient)//

It is important to isolate the infected people so as not to spread the pathogen.
 * Pathogen**: A disease-causing foreign substance. Some bacteria are pathogens. (From Greek “//páthos//” and Greek “//genés//”, meaning born)

Bacteria are prokaryotes.
 * Prokaryote**: A cell that lacks a nucleus. (“pro” meaning before, “karyote” meaning nut)

Refrigerators cool down and freeze food for a long time so that bacteria cannot infect it.
 * Refrigerator**: A device that cools down objects inside to a low temperature. As some bacteria cannot survive for very long in cold conditions, a refrigerator is also good for getting rid of disease-causing bacteria in food. (“Refrigerate” from Latin “//refrīgerātus//”, meaning to make cool)

Reproduction is necessary because life dies out, and if life dies out without first making copies of itself, then life has no successors and dies for good.
 * Reproduction**: The process of an organism making copies of itself. Without reproduction, life will die out. In bacteria, reproduction often occurs fastest at about 34 degrees Celsius. (from prefix “re,” again, and “//prōdūcere”//, meaning to extend, bring forward.)

Mushrooms make spores instead of seeds.
 * Spore**: Reproductive cells produced by fungi, which can grow without meeting another spore. (from Greek “//sporá,”// meaning “seed”)

It is important to sterilize bandages so they will not also introduce more pathogens into a wound.
 * Sterilization**: The process of heating something to high temperatures for a prolonged period of time. Since most bacteria cannot survive for very long in high temperatures, they die. This is used to get rid of any possible disease-causing bacteria in food. (From Latin “sterilis”, meaning unfruitful, and suffix “ize”, meaning to make)

The temperature of an object rises when heated.
 * Temperature**: The measurement of the speed of individual atoms in a substance. Higher temperature implies faster speed of the atoms. (From Latin undefined 0:0:0}

BIG IDEAS:



Temperature is one of the factors that limit bacteria growth. For example, sterilization heats the bacteria to high temperatures, killing them after a while. One of the dishes was placed in an environment where the temperature was set to 38.5 degrees Celsius, resembling fever temperature. There were fewer bacteria colonies in this dish than in the dish in the incubator at 34 degrees, resembling normal body temperature. This explains why fever is a good way to kill off bacteria when they invade the body. By raising the body temperature, the body helps to kill off the invading pathogens.

(green represents bacteria colony)

All living things need nutrients to survive and carry out life functions, and bacteria are no different. The agar produces all the nutrients needed to grow colonies. However, over time, as the bacteria absorb more and more nutrients from the agar, some nutrients will start to disappear. This nutrient depletion hinders bacteria growth and will eventually kill off the colonies as the bacteria run out of nutrients.

References:

Miller KR, Levine JS. //Biology//. Upper Saddle River, New Jersey: Prentice Hall; 2006: 470-492, 514, 1087-1104.