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Biology 3340: Identification of Unknowns: 100 points ( 3 weeks time frame)
The basic skills learned in the microbiology lab will be put to the test. In order to get all points
for this
exercise, you must correctly identify the two unknown bacteria given in a mixed culture. To do
this, you
must be able to effectively streak plate, perform stains, use a microscope and apply and
interpret
biochemical tests.
You may use course materials and reference books; however, you are required to do your own
work. You are NOT permitted to get help from other students in the class, the instructor,
student lab prep workers or other persons. You are NOT permitted to help other students in
the class. No cultures are to be taken out of the class. Any student who is caught attempting to
gain an unfair advantage from others, give an unfair advantage, or use laboratory resources
outside the teaching lab, will receive a zero for the entire lab grade. All the skills needed to be
successful on this assignment have been used over the course of the semester. Be confident in
your ability.
A broth culture containing any two organisms from the following list will be given to each
student. BE
SURE TO RECORD THE CODE NUMBER OF YOUR UNKNOWN. The student will be given
two TSA
plates on which to streak the broth in order to separate the two organisms. You have two plates
to do it
correctly. No additional plates will be provided for this step.
Bacillus subtilis
Enterobacter cloacae
Enterococcus faecalis
Escherichia coli
Micrococcus luteus
Salmonella enterica
Pseudomonas aeruginosa
Serratia marcescens
Staphylococcus aureus
Staphylococcus epidermidis
If you successfully separated your unknowns on the TSA plates, you will then need to establish
pure
cultures and identify the unknowns using any of the following supplies:
Gram stain reagents and slides, endospore stain reagents and slides, 2 TSA plates (for
establishing pure
cultures), 1 mannitol salt agar plate, 1 eosin methylene blue agar plate, 1 Salmonella-Shigella agar
plate,
2
oxidase reagent and cotton swabs or filter paper, 3% hydrogen peroxide, 1 glucose fermentation
tube, 1
sucrose fermentation tube, 1 lactose fermentation tube, 1 MR-VP broth, 1 sulfide-indole-motility
agar
tube.
Many of these tests are appropriate for only one type of organisms or another. For example, you
are
wasting your time and are heading in the wrong direction if you plate a Gram positive
bacterium on an
eosin methylene blue agar plate or Salmonella-Shigella agar plate. I suggest you start with
staining. On
the basis of those results, come up with a strategy to effectively use the supplies available.
Once you have identified your organisms, you will submit a typed report. The report must have
your
name and unknown code number. You then have the following options of how detailed you
want your
report to be. Think well before you choose one of the options
below:
OPTION 1: All or Nothing ( Type your report)
Name of first unknown. If correct 50, if wrong 0
Name of second unknown. If correct 50, if wrong 0
OPTION 2: Table of Results ( type your report)
Name of first unknown and a table of tests run and results for first unknown. If correct 50, if
wrong 0-15.
Name of second unknown and a table of tests run and results for second unknown. If correct 50,
if wrong
0-15.
OPTION 3: Well Defended typed Report ( include all pictures)
State the objectives of the experiment.
A brief introduction to identifying bacteria.
Name of first unknown and a table of tests run and results for first unknown. Explain your
strategy and
reason for each step you used to identify the unknown. If correct 50, if wrong 0-25.
Name of second unknown and a table of tests run and results for second unknown. Explain
your strategy
and reason for each step you used to identify the unknown. If correct 50, if wrong 0-25.
Refer to the syllabus as to the time and date the reports are due.