Download Bacteria Lab - North Allegheny School District

Name(s):______________________________________ Per_______
Bacteria Lab
Bacteria are microorganisms that grow everywhere. Bacteria are prokaryotes (Kingdom
Monera), which means that they have no true nucleus. They reproduce by binary fission.
Most bacteria are benign (benign = good, friendly, kind) or beneficial, and only a few are
“bad guys” or pathogens. Agar is a gelatin-like substance with a semi solid surface on
which the bacteria can grow while they consume the added nutrients.
You have heard of antibiotics and at some point in your life antibiotics were probably prescribed
to cure an illness you had. In Part 2 of this investigation, we will use discs that have been
impregnated with various antibiotics. These discs will be placed on petri dishes containing
bacteria. The purpose of the lab is to determine which of the antibiotics tested would be most
beneficial in treatment by observing the effect of two different antibiotics on the growth of the
bacteria. The procedure in this lab is similar to the one used in hospitals to determine which
antibiotic should be prescribed to treat a patient’s bacterial infection.
Antibiotic sensitivity is a term used to describe the susceptibility of bacteria to antibiotics.
Antibiotic susceptibility testing (AST) is usually carried out to determine which antibiotic will be
most successful in treating a bacterial infection. Testing for antibiotic sensitivity is often done by
the Kirby-Bauer method. Small wafers (discs) containing antibiotics are placed onto a plate upon
which bacteria are growing. If the bacteria are sensitive to the antibiotic, a clear ring, or zone of
inhibition, is seen around the disc indicating poor growth.
Tetracyclines are a family of antibiotics, all products of Streptomyces. Tetracyclines block
protein synthesis on isolated ribosomes. It concentrates in certain types of ribosomes possesed
only by bacteria, so it is not toxic to the animal. Because of their extremely low toxicity, they
were overused in the medical community, and now there is widespread resistance to tetracyclines.
However, they are still useful in treatment of some diseases, such as Lyme disease.
Streptomycin is a protein synthesis inhibitor binding to bacterial ribosomes to prevent the
initiation of protein synthesis. Aminoglycoside usage has been limited because prolonged use has
been found to cause kidney damage and injury to the auditory nerves, leading to deafness.
Problem: Comparing a variety of surfaces found in a school building, what surface
would have the most bacteria on it?
Hypothesis:
Part 1 Experiment:
Materials – cup with water, 2 swabs, Petri dish with nutrient agar, marker
Procedure –
1. Use a marker to divide bottom of Petri dish into 2 quadrants.
2. Put your last name on bottom section of Petri dish (part with agar)
3. When you arrive at the location for sample 1, pull out sterile swab and
moisten in small amount of water. Thoroughly cover area with
moistened swab and then quickly open Petri dish and inoculate dish by
streaking a pattern gently across the agar surface without tearing into
it. Streak quadrant 1 (1/2 of dish). Quickly reclose Petri dish and
dispose of used swab.
4. Repeat step 3 for the other area.
5. Upon return to class, invert Petri dish (agar now on top) and place on
tray. Return marker to front table.
Shapes/Forms
Observations: Record the appearance and number of colonies in the cart below.
Area #1
Colony
Description
# of
Colonies
Peroxide
Test ( + )
Morphology
(shape)
Colony
Description
# of
Colonies
Peroxide
Test ( + )
Colony
Description
# of
Colonies
Peroxide
Test ( + )
Morphology
(shape)
Area #2
Part 2 Experiment
Hypothesis:
1. Each partner should choose one colony to do an antibiotic susceptibility test.
2. Get a new agar plate. One for the 2 of you.
3. Take a sterile swab and very carefully touch the one colony that you want to test
and place in broth tube.
4. Swirl swab to mix. Press against sides of tube and then evenly swab ½ of plate.
5. Dispose of swab.
6. Place 2 antibiotic discs to test. Drop these onto plate spaced well apart. Tap
gently.
7. Next partner should repeat steps 3-6
8. After one to three days of incubation, observe results without opening the petri
dish.
9. Use a ruler to measure the DIAMETER (in millimeters) of the zone of
inhibition around each disc and record your observations in the table provided.
Bacteria Colony
Decription
Tetracycline Zone of
Inhibition (mm)
Strptomycin Zone of
Inhibition (mm)
You each will be typing your own formal lab report!! This template is
provided for you. Use all headings.
Name:____________________________________
Title of Experiment: ________________________
Purpose:________________________________________________________
Background: (List the facts necessary to formulate a hypothesis and design the
experiment.)
_______________________________________________________________
Formulation of Hypothesis I ______________
Formulation of Hypothesis I_______________
Independent Variables
(IV):___________________________________________________________
Dependent Variable (DV): the diameter
of______________________________________________________
Controlled Variable(s) (Constants)
(CV):______________________________________________________
Materials & Equipment: List materials and equipment below. A “material” is
something that is used during the lab and is disposed of when the lab is
finished . “Equipment” is anything that can be saved to use over.
Materials
Equipment
__________________________ ________________________
__________________________ __________________________
__________________________ __________________________
__________________________ __________________________
__________________________ __________________________
__________________________ __________________________
__________________________ __________________________
__________________________ __________________________
Procedure
Safety (Describe all safety precautions necessary in the experiment):
__________________________________
Procedure (Read the narrative description of the procedure provided on an
earlier page. Rewrite this procedure in your own words as numbered steps. It
should be detailed enough that the entire procedure could be recreated if
someone wanted to repeat your experiment.)
_______________________________________________________________
Data: Include your data tables
Data Analysis:
Predictions (If you were to complete an additional trial of this experiment,
what other outcomes would you expect?):
_______________________________________________________________
Accuracy/Precision (Discuss if the data collected is accurate and precise.
NOTE: Accuracy refers to how closely a measured value agrees with the
correct value.
Precision refers to how closely individual measurements agree with each
other.
Provide specific instances in which there could have been errors made.
Accurate?______________________________________________________
Precise?________________________________________________________
Sources of possible error?
_______________________________________________________________
Conclusion: This section should be written in paragraph form.
Restate the problem
In this lab, an attempt was made to answer the following question/solve the
following problem:
Restate the hypotheses
Support / Refute Hypothesis
Which hypotheses were
supported?______________________________________________________
Which hypotheses were refuted
(rejected)?_____________________________________________________
If any hypotheses were rejected, develop new hypotheses or explanations
based on experimental results:
How could you improve this experiment for future students to help reduce
potential sources of error? (Refer
to your list of observations of potential sources of error).