You
will identify an unknown bacterium based on a series of biochemical tests you
perform in lab. Your unknown will be one
of the following: Enterobacter aerogenes, Escherichia
coli, Proteus vulgaris, or Pseudomonas aeruginosa. Please review your section’s data for labs 5
and 6 for the expected results of each of these species, then compare these
results to the observations for your unknown, collected independently in Week 8
of laboratory.
The
template for your lab report can be found on page 3-4 of this document. Please use the template to complete your
report. The different parts of the unknown report and a description of what you
should write for each part of the report,:
A. TABLE:
A
table of your observations and results for all the tests you performed. Please
be sure to include your unknown number on the table. (30 points)
a. In the
column titled “observation”, you will type what you see (in many cases this
will be the color of the medium; make sure you add details such as if this
color appears after adding a reagent).
b. In the
column titled “Result”, you will type whether your unknown is positive or
negative for the specific biochemical reactions, and indicate the process
responsible where applicable (for example, positive for mixed acid fermentation,
or negative for hydrogen sulfide production).
c. In the
column titled “Explanation of Result”, briefly explain what your result means
in terms of enzyme production or biochemical reaction to a particular
reagent. In other words, WHY is the test
positive or negative, and what does that mean the bacterium can or cannot do? DO
NOT SIMPLY RE-STATE THE NAME OF THE TEST! What is happening to the reagents
or the pH of the media?
d. In the
column titled “Organism(s) indicated”, list the species tested that would share
this result based on your section’s control results collected in Weeks 6
and 7 of lab.
B. Report:
a. State
the full species names of each unknown (formatted correctly) and your goal for
this exercise. (5 points)
b. Since sugar
fermentation is an important first step in bacterial identification, you will
write about your results for the fermentation tubes (phenol red glucose,
lactose and mannitol) and OF glucose. Focus on your results (not observations) and explain how carbohydrate metabolism helped
you identify your unknown, including which bacteria you were able to eliminate
based on the results obtained. Explain,
through a process of elimination, how you eliminated the bacteria that were
not your unknown based on your fermentation and OF glucose results. Be
specific, mentioning the bacteria you knew your unknown could possibly be or
not be based on your results of the phenol red fermentation tubes and OF
glucose. This will lead you to a presumptive identification of your
unknown. Clearly state which of
the given species you think may be your unknown based on these test results
considered together. Please do not include a description of the
procedures you performed. (15 points)
c. Now
that you have a presumptive identification for your unknown, you will need to
confirm the identification. You will do
this by writing about the definitive tests that identify the unknown you
have. A definitive test is one that is
used to identify a specific bacterial genus or distinguish two closely related
organisms. For this part of your report, you will discuss the results of the
definitive tests that allowed you to identify your unknown, beyond the sugar
fermentation you described in Part B. Explain, through a process of elimination,
how you eliminated the bacteria that were not your unknown. DO NOT
DISCUSS ALL OF THE TESTS YOU PERFORMED. You will lose points for describing tests
that are not definitive tests for your particular unknown. If there are any tests with conflicting
results to the controls, that made it difficult to identify your unknown,
mention them and provide a possible reason for the conflicting result. (40 points)
d. In
part D, identify your unknown as one of the following: Enterobacter
aerogenes, Escherichia coli, Proteus vulgaris, or Pseudomonas aeruginosa, and summarize,
based on a brief recap your results, why this is the case. (10 points)
