Identification of a Bacterial Unknown

Expectations for Identification of a Bacterial Unknown,
Examine your streak plate
• Critique your streak plate & determine if the culture is pure
• Observe colony characteristics
• Record your observations in Table 1
Examine the aerobic and anaerobic plates to determine oxygen requirements
• Record your observations in Table 1
Formulate a testing strategy by constructing a dichotomous key.
• Use the Biochemical Test Student Database to construct a dichotomous key.
– A dichotomous key uses a series of “either-or” choices to progressively whittle
down a large pool of organisms into smaller and smaller pools until each
organism can be individually identified.
– You will begin with the pool of 17 organisms. You will then select a staining
procedure or biochemical test that divides the pool roughly in half. (Think of a
bracket system.) You will then select another staining proceeding or test to
divide the half pools of organisms in half again… and so on and so forth.
– IMPORTANT: You may use a biochemical test more than once.
• Suggestions for constructing a dichotomous key:
– Use the Biochemical Test Student Database to select tests that give an “either or” result (+ or -).
– Start with the Gram reaction
– Select a biochemical test that divides the organism pool into two roughly even
groups. This works well early on.
– Select a biochemical test that identifies something unique about each organism.
This works well at the end.
• Upload your completed Dichotomous Key to Blackboard by the specified deadline.
– This dichotomous key will be graded. (15 points)
– Include both Gram positive organisms and Gram negative organisms on your
dichotomous key
– Key must be clear and legible – Must be typed or neatly hand-written
– Key must include all 17 organisms. Use proper nomenclature.
– Write out the full names of biochemical tests and stains (no abbreviations)
– File must be properly titled, formatted, and uploaded to Blackboard

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