Lab 127 Day 2

BI 127 Microbiology Lab Online Identification of a Bacterial Unknown #2

Fall 2020

Expectations for Identification of a Bacterial Unknown, Day 2

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

• NOTE: You are welcome to change your testing strategy after the original dichotomous key is submitted for grading. Simply attach your revised dichotomous key to the end of the Written Laboratory Report.