Bacterial Growth in the Boys' and Girls' Living Envrionments of Peabody Hall

This topic submitted by Donald, Tekk, Ashley, Eric ( at 1:50 pm on 12/6/01. Additions were last made on Wednesday, May 7, 2014. Section: Wagner

This lab was designed to enable students to gain a familiarity with the bacteria in their everyday environment, as well as to give them an introduction to procedures used to collect bacteria and grow bacteria to be studied. In this lab, we ask the students to (1) collect various samples of bacteria, and (2) learn and use proper streak plate techniques so that the data can be easily classified according to how much bacteria is in a sample.
The lab was concerned with the Boys’ and Girls’ Living Environments of Peabody Hall (3rd and 2nd floors respectively) and which one was dirtier based on the amount of bacteria found. The lab found that the Girls’ Living Environment was dirtier based on the collection data. Statistically the Boys’ and Girls’ Living Environments presented no significant differences according to a T-test comparison.

To get you more excited about the experiment here are some interesting facts and history of bacteria. Although bacteria live all around of us, most of it is relatively harmless. In fact, only a very small fraction is harmful to us humans (Encarta Online 2001). However, the effect of these few harmful bacteria can be lethal. During the Middle Ages the “Plague” or “Black Death” ravished Europe between 1348-1351 somewhere between 25 and 35 percent of the population died. In certain cities, villages, and areas the number of deaths soared to 60% or higher (Noble et al. 1998). The name of the bacteria that caused this death is Yersinia pestis, and was spread by rats. Another notable outbreak was of Cholera (Vibrio cholaerae) that hit Europe and Asia in the 19th century, and as recently as the 1990s was found in South America. One final bacterial disease is tuberculosis (Mycobacterium tuberculosis), which has claimed millions of human lives throughout human history (Encarta Online 2001). For these reasons, people want to be more aware of the bacteria that they interact with on a daily basis for individual self-knowledge and health. Another common bacteria that live on us that is of health concern is Staphylococcus. This nasty little thing lives in the air and water and on the human body typically on the upper pharynx (throat) and is responsible for pneumonia and septicemia (Encarta Online 2001).
The Dutchman Antoni van Leeuwenhoek recognized bacteria in the late 17th century. He was a microscope maker and spent many hours grinding and regrinding the glass for his microscopes. He was the first person to describe what he discovered under his lens (Encarta Online 2001). It is due to van Leeuwenhoek that we are able to see bacteria and are thus able to do this experiment.
Since bacteria are so common many people are familiar with them. Have you ever stopped to think about how much of a role bacteria play in your daily life? Encarta Online Encyclopedia states that bacteria are:
[M]icroorganisms that lack a nucleus and have a cell wall composed of peptidoglycan, a protein-sugar molecule. Bacteria are the most common organisms on earth and are intimately connected to the lives of all organisms.
Bacteria are small and are everywhere. This experiment is designed to show that bacteria live all around us, and are part of our daily lives.
In this experiment the boys’ and girls’ living environments of Peabody Hall (2nd & 3rd floors) will be sampled for bacteria. The bathrooms on each floor and two dorm rooms on each floor will be used for the study. In each of the designated zones (See diagrams for individual specimen zones) samples will be collected and then allowed to grow in Petri dishes. After the maturation process of the bacteria each sample will either be labeled 1- high bacterial growth, 2- medium bacterial growth, 3- low bacterial growth, or 4- no bacterial growth. Based on the amount of bacteria found to have grown in the Petri dish, a point value will be assigned to each. The living environment with the highest bacteria count (based upon total points) will be declared the dirtiest, and will be the recipients of the coveted Dust Bunny Award, which they can then proudly, and rightfully, so display. This is the first, and hopefully annual, competition between the girls’ and boys’ living areas of Peabody Hall for the coveted Dust Bunny Award. On completion of the experiment, each researcher will be able to collect bacteria samples and use proper streak plate techniques.
The purpose for doing this experiment is to discover whose living environment is dirtier, the boys’ or girls’. The Null hypothesis is that neither living environment will have more bacteria than the other. The research hypothesis is that the boys’ living environment (3rd floor) will have more bacteria then the girls’ living environment (2nd floor).
This experiment is designed to enhance the understanding of bacteria and increase the awareness of the quantity of bacteria around us. Because they cannot be seen with the naked eye, we often forget about bacteria and the repercussions they can have on our health. Consequently, sometimes humans are careless and may be exposing themselves to harmful bacteria. We hope this lab will remind us of the importance of cleanliness.

This friendly little guy’s name is Clostridium botulinum and causes botulism poisoning. (
Cotton swabs
Petri dishes
Cellophane tape
Masking tape
Pen, pencil, marker
Latex gloves

We based this experiment in part on the Miami University’s MBI 123 class and their labs.

Samples of bacteria were taken from various locations on the second and third floors of Peabody hall. Locations included the sinks, showers, toilets, and door handles of the bathrooms and keyboards, computer mice (which was not done in the actual experiment) and door handles from dorm rooms (See Diagrams1-3 for more detail). This was done by taking cotton swabs and streaking them on the sampling areas mentioned above. A streak plate technique was used in order to measure whether there was many bacteria, few bacteria, or no bacteria. In the Petri dish we streaked the cotton swabs seven to ten times on one half (Side A) and two to four times on the other (Side B)(Figs. 1 & 2). The amount of bacteria was determined by the growth on either half of the dish. If there was no bacterial growth on the entire plate then it received a score of 0. If there was low bacterial growth on the heavily stroked half of the plate and none on the lightly stroked half than it received a score of 1. If there was high bacterial growth on the heavily stroked side but none on the lightly stroked side it received a score of 2. If there was high bacterial growth on the entire plate then it received a score of 3. A simple spreadsheet was used to calculate the results. Data was entered into the spreadsheet and using addition the point values for each floor the total was tabulated. The floor that received the highest score was deemed the dirtiest and received the Dust Bunny Award.

1) Go to designated area with your materials (you will receive your location and materials in seminar)
2) Remove a cotton swab from the package. Do not touch either end of the cotton swab.
3) Wipe one end of the cotton swab on the designated surface.
4) Open Petri dish.
5) Wipe the end of the cotton swab about seven to ten times on one half of the agar. Then wipe the same end of the cotton swab on the other half 2-4 times. (See Fig. 1)
6) CLOSE PETRI DISH! Leaving it open can allow bacteria in the air to contaminate the sample.
7) Tape Petri dish closed with cellophane tape.
8) Make sure Petri dish will not open.
9) Really, if it opens the sample will be no good.
10) Record place (location number) and time on a piece of masking tape and apply it on the top of the dish between the two halves (See Fig. B).
11) Return the Petri dish to the location where you received it.

Fig 1 Fig 2



List of Sample Areas
Bathrooms (North & South)
1. Below Seat Back
2. Seat Cover Back
3. Seat Cover Side
4. Toilet Handle (Flusher)
5. Bathroom Door Handle (Inside)
6. Sink Handle Knob (Hot)
7. Sink Drain
8. Paper Towel Dispenser Knob
9. Shower Drain
10. Shower Handle/Knob
Dorm Rooms (2 on each floor)
1. Light Switch
2. Door Handle (Inside)
3. Left Mouse Button

The research timeline was quite simple. One day during Natural Systems seminar all the sampling was done with the help of the class. The samples were allowed to grow for one week. After the growth process we then examined the Petri dishes to determine the amount of bacterial growth. A T-test was used to determine if the amount of bacterial growth differs between the boys’ and girls’ living areas.
Day 1 – swabbed Petri dishes
2 - growth
3 - growth
4- growth
5- growth
6- growth
7- growth
8- Petri dishes were observed and checked for bacterial growth, then point values were assigned to each dish.

Sample numbers 13,26 were not used in both the Boy’s and Girl’s Living Environments due to lack of Petri dishes when the experiment was preformed. The numbers have been left in the spreadsheet to show that they should be used for a better understanding and comparison between the two living areas if there is no limitation on the amount of Petri dishes available. A letter D indicates the sample was taken from a dorm room.
Mold, fungi, and maggots were found to grow in the Petri dishes. The dishes were marked if there contained mold, fungi, or maggots. (See the filled in Data Sheet). The total number of Petri dishes that had either mold, fungi, or maggots in them were added up.

BacterialGrowth High (3pts) Medium (2pts) Low (1pt) None (0pts) Points
(1-13 North Bathroom/Dorm rooms & 14-26 South Bathroom/Dorm rooms)
1 X 1
2 X 1 MOLD
3 X 1
4 X 1
5 X 1 MOLD
7 X 3
8 X 2
9 X 3
10 X 1
11d X 1
12d X 0 MOLD
South Bth/Dm
14 X 1
15 X 1 MOLD
16 X 2 MOLD
17 X 1
18 X 0
19 X 0 MOLD
20 X 3
21 X 1
22 X 3
23 X 1 MOLD
24D X 1 MOLD
25D X 2 MOLD
21 9 - MOLD

BacterialGrowth High (3pts) Medium (2pts) Low (1pt) None (0pts) Points
(1-13 North Bathroom/Dorm rooms & 14-26 South Bathroom/Dorm rooms)
1 X
3 X 1 MOLD
4 X 1 MOLD
5 X 2 MOLD
7 X 3
8 X 2
10 X 3
11D X 1 MOLD
South Bth/Dm
14 X 1 MOLD
15 X 1 MOLD
16 X 1 MOLD
17 X 1 MOLD
18 X 2 MOLD
19 X 1
20 X 3
21 X 2
22 X 3
24 X 0 MOLD
25 X 1
35 10- MOLD


The Girl’s Living Environment had more bacterial growth as determined by the point total. The Girl’s had 35 points as opposed to 21 for the Boy’s. The Girl’s also had more fungus, mold, and maggots. The totals being: Girl’s- 10 mold, 4 fungus, and 1 maggot (numbers corresponding to the amount of Petri dishes with the aforementioned type in them). The boy’s had 9 molds and 1 fungus. The p-value was 0.7509 that is greater then 0.05 thus we accept the Null Hypothesis.
After completing our research on the bacteria present in the living environments of Peabody Hall, it was discovered that the hypothesis was incorrect. The girls’ floor of Peabody Hall was found to have slightly more bacterial growth than the boys’ floor, particularly in the bathrooms. However, this difference was insignificant. The p-value of 0.7509 demonstrated that there was no significant difference between the boys’ and girls’ living environments. The hypothesis that boys’ living environments would be dirtier than girls’ was based on a stereotype. However, upon further inspection, if this stereotype is true, it may actually lead to cleaner bathrooms because they spend much less time in them. This experiment may not have been entirely accurate as to who is dirtier because the way we interpreted the results was so ambiguous. The data was expected to be fairly easy to interpret and straightforward. Instead, it was found to be difficult to categorize the data and assign a point value of one, two, or three. Often the amount of bacterial growth that was found in various cultures fell somewhere in between two categories. The growth of molds and fungi in the samples were not expected to the extent that they occurred, and the technique in the experiment was not prepared to account for them in the data. The growth was noted in the data, but did not influence the conclusion as to who was dirtier.
If the experiment were to be done a second time, it could have been improved by researching what the growth of fungus and mold tells us about the bacteria that would be present. The categories used for classification of the growth would be more precise. A point value could be assigned based upon the level of disease causing bacteria found in the Petri dishes. This might present a better understanding of who is dirtier, meaning who is likelier to get sick. Another possibility of categories is by weight. The dishes could have been weighed before and after the experiment to determine the mass of bacterial growth. A point value would be assigned to different masses or the masses could simply be added together to find which floor had the most bacterial mass grow in the allotted time frame of one week. The streak plate technique could have been expanded. Instead of only two areas one with low streaks and one with high the experiment could use three or even four different areas of various streaking. This might allow for easier classification under a point value system similar to the one used in this experiment.
If the experiment was to be taken further there are many things that one may want to look at. The type of bacteria, mold, and fungus present could be identified. What each type does is it safe, how long does it live, and how common is it? Are all questions that could be asked and answered if the experiment were to undergo further investigation.

Works Citied
“Bacteria”. Microsoft Encarta Online Encyclopedia 2001 (2 Oct.
Board, R.G., Jones, Dorothy, & Skinner, F.A., (1992), Identification
Methods in Applied and Environmental Microbiology. Blackwell Scientific
Noble, Thomas F.X., Strauss, Barry S., et al. (1998) Western Civilization: The
Continuing Experiment. Houghton Mifflin Company.
Singleton, Paul, (1992) Introduction to Bacteria: For Students of Biology, Biotechnology,
& Medicine. John Wiley & Sons.
"Staphylococcus," Microsoft Encarta Online Encyclopedia 2001 (2 Oct. 2001).
Ohio State (Lima) Website: (2 Oct. 2001).
Suggested Readings
Bartlet, Margaret A., (2000) Diagnostic Bacteriology: A study guide. F.A.
Davis Company.
Isaac, Susan and Jennings, David, (1995) Microbial Culture: Introduction to
Biotechniques. BIOS Scientific Publishers Limited.

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