EXERCISE 58
IDENTIFICATION OF UNKNOWN ORGANISMS
You have been given a mixture of three microorganisms to identify. Your chance of successful identification will be greater if you follow some simple steps.
1.
2.
3.
4.
Isolate pure colonies using streak plate techniques.
Verify your original gram stain using your pure cultures.
Put your pure cultures on slants to use as stocks for your tests.
Construct flow charts and proceed with diagnostic tests for identification.
REMEMBER:
Work independently. You are to receive no assistance from your fellow students, your TA, the lab coordinator, Dr. Reeves, etc. on interpretation of Gram
stains or tests. You may work only from the notes in your lab book and text.
You are required to turn in the "Unknown Report" form included in this packet as well as your flow charts (original and revised) and the written report with your
problem analysis, microbial profiles, and other information requested by your TA.
You may be penalized for carelessness. You will lose points if you do the following:
1.
2.
3.
If you need more than 5 TSA plates for isolation because you forgot to move your plates after 24 hours.
If you perform an inappropriate test thus wasting media.
If you perform tests on an impure culture or the wrong culture because you forgot which culture was which.
Your grade will be based on the following information:
Gram reaction and Cell Morphology
Streaking for isolation
Flow charts
Identification of organism
Written portion
3 X 5 pts =
3 X 5 pts =
3 X 5 pts =
3 X 20 pts =
15 pts
15 pts
15 pt
60 pts
45 pts
_____________________
150 pts
GOOD LUCK AND HAPPY STREAKING!
UNKNOWN RESULTS - REPORT FORM
NAME:___________________________
SECTION #:_______________________
Attach flow charts, problem analyses, microbial profiles, etc.
UNKNOWN NUMBER:
Unknown #1
MICROORGANISM'S IDENTITY
Gram stain reaction
Cell shape
Colony morphology
Growth in TSA Deep
Lactose fermentation
Indole production
Methyl-Red test
Voges-Proskauer test
Citrate utilization
Gelatin hydrolysis
Catalase test
Growth on High Salt (7.5%) agar
Mannitol Fermentation
H2S production
Confirmatory tests:
Unknown #2
Unknown #3
COMMENTS
UNKNOWN RESULTS -- PREPARING THE REPORT
Your unknown results will be graded according to the procedures you chose to use, the results you obtained, your analysis of any problems that occurred, and what you can
conclude about the microorganisms you were issued based on your results. The following is an outline of what you should include in your unknown report. Note: your
instructor may add to this outline.
1)
Unknown results - report form
This form is printed on the reverse side of this page. The form should be filled in according to the tests you actually did and the results you actually obtained.
Comments about tests that you feel are inconclusive or in error should be made in the space provided, and elaborated on in the problem analysis if necessary. You should also
indicate tests that you used to confirm the identities of your unknowns when you have used such tests.
2)
Flow charts
Any flow charts that you have constructed to guide you in identifying your unknown should be attached. It is possible that you have more than one set of flow charts
due to changes you made during the course of identifying your unknown. Mainly, it is important that your TA understand exactly what you did. If problems in following your
original or any revised flow charts occurred, you should provide details in your problem analysis.
3)
Problem analysis
Many students will have had problems in identifying their unknown, or might be unsure about results they obtained. While some problems may have been resolved
easily, others may have taken quite a bit of time and energy, or may have been resolved through intervention by the TA. It is critical that students be able to identify and
articulate problems or uncertainties, explain possible reasons, provide information about how the problem was resolved (if it was resolved), and propose how any problems or
uncertainties could be prevented in the future. Students should also be aware that each TA has been keeping track of each student's progress, so most of these problems have
either been identified or anticipated based on what the TA has observed.
All students should turn in an organized and concise analysis of any problems or concerns that includes the information detailed above. Keep in mind that your grade
will not be based on the length of your report. Many students can complete this portion in less than one page.
4)
Microbial profiles
After identifying your unknown, it is important that you understand what your test results "tell you" about the microorganisms you were issued (i.e., a positive gram
stain tells you something about the cell wall). You should prepare a short "microbial profile" for each microbe, which reflects that you know what you were testing for and
what your results mean with regard to each organism.