bacterial species based upon the results of their differential
staining and growth on selective and differential agar plates.
4. Encourage students to generate a confirmatory test to show
that B. amyloliquefaciens is the microbe that causes “peep
pox.” Three suggestions for testable hypotheses are:
• Since the spore stain showed B. amyloliquefaciens forms
endospores, but E. coli and S. aureus do not, it is expected
that B. amyloliquefaciens should survive pasteurization of
• Purified B. amyloliquefaciens is expected to hydrolyze gelatin using the gelatinase test.
• B. amyloliquefaciens is expected to grow on a “peep plate”
(analogous to the creation of a blood agar plate using red
Advantages of this approach to teach
Koch’s postulates in a microbiology
1. Safety. All three bacterial species used are BSL-1 level
Figure 2. Diagram of steps needed to fulfill Koch’s postulates for “peep box.”