Delehanty 1

“Bacteria is Gross” –My sister

Sam Delehanty

Mrs. Britt

Honors Biology

2 February 2015

Delehanty 2

Introduction

Bacteria are microorganisms that then reproduce themselves to form a

bacterial colony. Mold is a fungus that comes from plants, animals, or bacteria.

Mold becomes fuzzy because of the hair-like bodies it forms onto the surface. Both

bacteria and mold grow best under warm environments. Agar is a gelatinous

substance that comes from different seaweeds. Agar is the most widely used

substance for culturing bacteria and mold because of its inability to be eaten by

bacteria.

In the bacteria experiment there is an independent variable, dependent

variable, and a control. In the experiment the independent variable is the type of

bacteria being tested. The dependent variable is the amount of bacteria, or mold,

being grown. The control in the bacteria experiment is the amount of agar, type of

agar, container, environment for growth of bacteria, and temperature that the

bacteria are stored in.

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Procedure

Step 1: Get a petri dish with about ¼ inch agar.

Step 2: On the back of the petri dish, draw four quadrants labeling them “A, B,

C, D”.

Step 3: Label quadrant A “control” .

Step 4: Find three other places to swab.

Step 5: Before swabbing the surface, take out the cotton swab, making sure it

comes into contact with nothing else.

Step 6: Lift the lid off the petri dish and swab only one quadrant in a

streaking motion, and then close the lid. Repeat for the two other quadrants.

Step 7: Once all quadrants, other than quadrant “A”, have been swabbed,

place the petri dish into the incubator.

Step 8: After 48 hours, take the petri dish out of the incubator and record

results. Then put the petri dish back into the incubator.

Step 9: After 120 hours since the petri dish had first been put into the

incubator, take it out and record the results.

Data

Location 1 (or A) = ControlLocation 2 (or B) =Hand railing in HockenburyLocation 3 (or C) =Café microwaveLocation 4 (or D) = Trash can lid48 Hours

Delehanty 4

Petri Dish Selection Object or Surface

Tested

Number of Bacteria

Colonies

Color Other

A Control. 0 N/A None

B Hand Railing 8 White/Yellow Small colonies

spread apart

C Café Microwave 7 Yellow Smears over the

agar; colonies are

not circular

D Trash can lid 6 White Small colonies;

smears on agar

48 hours

120 Hours

Petri Dish Object or

Surface

Number

of

Description of colonies

Delehanty 5

Selection Tested Bacteria

Colonies

Color Form Elevation Margin Other

A Control 0 None None None None None

B Railing 8 White/Yellow Circular Raised Entire Colonies

are not

touching

each other

C Café

Microwave

3+ very

small

spots

White/Yellow Square Very

Little;

umbanate

Lobate Colonies

are

beginning

to grow in

streaks

D Trash Can

Lid

8 White/Yellow Circular Raised Entire Circular;

variation

in size; all

colonies

grow far

from each

other

Analysis

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1. Which section of the Petri dish served as a control? What did this

prove?

a. Quadrant “A” served as the control. There was no bacteria growth in

this section, which shows it remained sterile, and serves as a control

for the rest of the quadrants and to the experiment.

2. If there are any colonies in the control section, how could you explain

this?

a. If the control section has bacteria growth then the section may have

been swabbed by accident.

3. According to your data, which are more common on surfaces you

tested- mold or bacteria?

a. Bacteria are more common on the surfaces that were tested.

4. Define bacteria colony.

a. A bacteria colony is a group of microorganisms, which become visible

after reproducing themselves and multiplying.

5. How many different types of bacteria colonies did you observe on the

entire dish? How can you distinguish different types of bacteria?

a. On the entire dish, there were two different types of bacteria colonies.

This can be determined by their elevation and margin.

6. Why is it necessary to incubate this dish before observation?

a. It is necessary to incubate the dish before observation because, in

order to observe bacteria, it must be visible and placing it in the

incubator helps to accelerate the amount of time it takes for the

Delehanty 7

bacteria to grow, since bacteria and mold will grow faster in a warmer

environment.

7. Why shouldn’t you open the dish to view the colonies?

a. It is important not to open the dish to observe the colonies because,

when the dish is opened, new bacteria is exposed to the bacteria

trying to be tested. This gives mixed results. Also, it would not be

wise to open the lid of the Petri dish because certain bacteria may be

let out and harmful.

8. Which surface that you tested had the most bacteria growth?

a. The surface that had the most bacteria growth was the hand railing in

Hockenbury. This may have had the most bacteria growth because it

is constantly being touched and is kept in a warmer environment.

Conclusion

Delehanty 8

In the lab there were three locations that were tested: The hand railing on

Hockenbury, the café microwave, and the lid of the trash can in the café. Each

location had a different surrounding which made it prone to different bacteria and

different amount of bacteria growth. The café microwave, quadrant “C”, is

constantly enclosed and exposed to heat, which helps to grow bacteria. Even

though, when swabbed, the location did not grow many bacteria, it grew different

bacteria than the other two locations, showing a sign that, if it had been incubated

longer, there may have been more growth and would have led to a more deeper

examination. The café microwave bacteria grew the least amount. Another

substance that was swabbed was the lid of the trashcan in the café, quadrant “D”.

While this did not grow as much bacteria as the hand railing, it still grew a decent

amount after being incubated for 120 hours. This may have been because it is

usually kept at a room temperature. The growth was not huge, but still noticeable

enough to leave a mark and make someone wonder what really lurks on the trash

can lid… The last place that was to be mentioned is the hand railing in Hockenbury,

quadrant “B”. This location grew the largest amount of bacteria; the constant

touching it gets by people’s hands when going up and down the stairs may have

caused this. The temperature that the bacteria on the railing would be kept at, room

temperature, could also have impacted the major growth. Out of all the bacteria that

was tested, the bacteria that had the most growth was the bacteria from the hand

railing. When examining the growth, it is easy to tell that the bacteria from the hand

railing and the trash can lid must be pretty similar because of their shape, margin,

and elevation. They were both circular, entire, and raised. It is easy to assume that

Delehanty 9

the bacteria must be from people’s hands. The hypothesis for this lab was that the

bacteria swabbed from the café microwave would coulter the most bacteria or mold.

This hypothesis proved incorrect; the bacteria swabbed from the hand railing grew

the most.