Download Bacterial Growth and Antibiotics

Objective – Observe and summarize information about microorganisms.
Bacterial Growth and Antibiotics
(an activity from Access Excellence)
Objective
Students will grow bacterial colonies and then determine the effectiveness of
antibiotics in killing the bacteria.
Background Information
Most bacteria can proliferate rapidly through binary fission. Under optimal conditions,
some bacteria can divide as rapidly as once every 20 minutes, a trait that has proved
invaluable to geneticists. However, until the 1940s, scientists were not sure that
bacteria would be useful subjects for genetics research because it seemed that their
method of reproduction was too simple. At that time, researchers found that although
bacteria do not reproduce sexually in the same manner as plants and animals, they do
have mechanisms for transferring genes from one individual organism to another.
These mechanisms allow bacterial strains to become resistant to antibiotics.
Many disease-causing bacteria respond to treatment by antibiotics, which are used to
kill or slow the growth of bacteria. Like antibiotics, antibiotics can also inhibit the
growth of certain types of bacteria. In this activity, students will study the effectiveness
of common antibiotics.
Materials
 Agar plate
 Sharpie
 Cotton swab
 Forceps
 Antibiotic discs
 Distilled water
 Tape
Objective – Observe and summarize information about microorganisms.
Procedure
1. Lightly moisten a cotton swab with distilled water.
2. Get a bacterial sample.
3. Carefully lift up the lid of your agar plate. Quickly streak the swab in a zigzag motion
all over the agar surface, and then replace the cover.
4. Using your forceps, place the four discs in four positions on your agar plate.
Carefully open the agar plate and place the neomycin disc (N) in the section labeled 1.
Place a chloramphenicol disc (C) in section 2, and a streptomycin disc (S), in section 3.
Place the blank disc in section 4.
5. Tape the agar plate shut and incubate them upside-down for 48 hours in the
incubator. (Incubating the plates upside-down prevents condensation from falling on
the bacterial colonies.)
6. After incubation, compare the diameters of the clear areas around each disc. DO
NOT! remove the cover of the plate while observing the bacterial colonies.
Objective – Observe and summarize information about microorganisms.
Names _____________________________________________________________
___________________________________________________________________
Absent _____________________________________________________________
Bacterial Growth and Antibiotics
Data and Analysis
(an activity from Access Excellence)
Before You Being Your Lab
1. Explain the purpose of in this lab.
___________________________________________________________________
___________________________________________________________________
2. What is your question?
___________________________________________________________________
___________________________________________________________________
3. What is your hypothesis?
___________________________________________________________________
___________________________________________________________________
Analysis
4. The agar plates were sterilized before this investigation. Why do you think this was
necessary?
___________________________________________________________________
___________________________________________________________________
Objective – Observe and summarize information about microorganisms.
5. Which antibiotic appears to be the most effective? How can you tell?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
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6. How can you tell if there is more than one type of bacteria growing on the agar
dish?
___________________________________________________________________
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7. Was your hypothesis correct? Explain why or why not.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
8. Which antibiotic has the most surprising result? Explain your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
9. How might you use the information you learned from this lab as a consumer?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Objective – Observe and summarize information about microorganisms.
N – Neomycin
C – Chloramphenicol
S - Streptomycin
Bacterial Growth and Antibiotics
Data and Analysis
(an activity from Access Excellence)
Before You Being Your Lab
1. Explain the purpose of in this lab.
Explore the effectiveness of antibiotics.
2. What is your question?
Which antibiotic is most effective killing bacteria?
3. What is your hypothesis?
Answers will vary.
Objective – Observe and summarize information about microorganisms.
Analysis
4. The agar plates were sterilized before this investigation. Why do you think this was necessary?
To prevent unknown bacteria from contaminating your experiment.
5. Which antibiotic appears to be the most effective? How can you tell?
Answers will vary. How can you tell – The area surrounding the most
effective antibiotic will be surrounded by the largest ring where there are no
bacteria.
6. How can you tell if there is more than one type of bacteria growing on the agar dish?
Bacteria look different. If you have bacteria that are different colors, colony
shape, size, etc., this means you have different types of bacteria in your sample.
7. Was your hypothesis correct? Explain why or why not.
Answers will vary.
8. Which antibiotic has the most surprising result? Explain your answer.
Answers will vary.
9. How might you use the information you learned from this lab as a consumer?
Answers will vary.
10. List two things you learned form this lab activity.
Answers will vary.
Objective – Observe and summarize information about microorganisms.
N – Neomycin
C – Chloramphenicol
S - Streptomycin