Download Effect of Tear on Bacterial Growth

Name:
Date:
Period:
Effect of Tears on Bacterial Growth
Introduction: Bacteria can survive in almost every environment on Earth. Why is
it, then, that we don’t get sick all the time? There are two kinds of immunity:
innate and adaptive. Innate immunity refers to immediate, non-specific defense
which does not depend on antigens. Adaptive immunity, on the other hand,
entails a specific antigen and results in immunological memory. In this lab, you
will explore the effects of tears, which contain the enzyme, lysozyme, on the
growth of bacteria.
Science Standards:
6a. Students know biodiversity is the sum total of different kinds of
organisms and is affected by alterations of habitats
10a. Organisms have a variety of mechanisms to combat disease. As
basis for understanding the human immune response:
Students know the role of the skin in providing nonspecific defenses
against infection.
Key words: lysozyme, bactericidal, bacteriostatic, serial dilution, inhibition, innate
immunity, adaptive immunity
State the Problem: How do tears affect bacterial growth?
Read through this lab and formulate your hypothesis.
Hypothesis: _____________________________________________________
Materials:
onions
E.coli: HB101 K–1lyophilized on LB/agar
inoculated filter paper discs saturated with dilutions of tears
micropipettes
microcentrifuge tubes
DI water
Incubator
Permanent markers for labeling
Procedure
1. Slice several onions in an attempt to stimulate tear formation in your own
eyes.
2. Swab corner of ears with filter paper. Place soaked filter paper into a tube
with 10uL DI water.
3. Label 4 microcentrifuge tubes with the 4 serial dilutions you will make:
1/.1/.01/.001
4. Make 4 serial dilutions of tears (1, .1, .01, .001) Transfer 5uL of tear
solution into 50 uL DI water. Make three dilutions total.
5. Label petri dishes so that there are 5 “pie slices” with tear dilutions
labeled.
6. Soak filter paper discs into each prospective solution
7. Add inoculated filter paper disc into appropriate quadrant
8. Incubate plates for 48 hours at 37C.
Making serial dilutions:
5uL
5uL
5uL
Add 5uL from each tube to
the adjacent tube to make
10-fold dilutions of tears
45uL
water
Tube # 1
10 uL tearsremove 5uL and
put into next test
tube
Tube #2
45uL
water
Tube #3
45uL
water
Tube #4
#4
4. Observations:
In the diagram below, record the 4 tear dilutions, one per “slice.” Indicate
approximate number of bacterial colonies in each quadrant. Show “zones of
inhibition” in each quadrant.
Dilution =
Dilution =
Control
Dilution =
Dilution =
Analysis Questions:
1. Why was the control in this lab?
2. Why is a control group necessary in this lab?
3. If you wanted to make 2-fold dilutions of tears (doubling the dilution each
time) with a starting quantity of 10uL tears, how would you make the
dilutions? Make a labeled drawing below.
4. Were there any other visible organisms on your plate? What possible
effect did it have on your experiment?
5. Explain how this lab relates to innate or adaptive immunity.
6. Conclusion
In 5 paragraphs, answer the following questions:
1.
2.
3.
4.
5.
Write a summary of the lab’s purpose, materials, and procedure
Re-state your hypothesis and explain whether it was right or wrong.
Summarize the lab’s result
What does the data indicate about the role of skin in human immunity?
What were some avoidable and unavoidable sources of error? How could
you extend this lab in an effort to explore the effects of tears on bacterial
growth?