Student Name: burton
Access Code (located on the lid of your lab kit): AC-OU2JH9B
Experiment 1- Selection and Differentiation of Body Inhabiting, Gram-Positive Bacteria
Table 4: Experiment 1 Growth
Conditions
Growth (Good or Poor)
Surface Tested Color Other
LB/Nutrie (Red or Observatio
nt Agar MSA Agar ns
Yellow)
White growth
present too.
Skin Good Good red Small Round
spores.
Same growth
as seen on the
Nose Good Good red skin but in
fewer
quantities.
Spores are
very few (2-
Countertop/Oth Poor Poor red 5).
er Nutrient agar
has a 1 large
colony.
1 small
Control poor poor red round
colony.
Post-Lab Questions
1. What substance in MSA confers selectivity? Why?
While MSA is both selective and differential, the high salt content is what makes it selective. This
environment will not allow certain bacterial cells to thrive making the plate selective to certain
, bacteria.
2. What substance makes MSA differential? Why?
MSA is differential due to its sugar source—Mannitol. This opens the window to a few more
bacteria making the plate differential too.
3. What purpose does phenol red serve in MSA?
The phenol is a pH level indicator. If the color is red, it is the bacteria is basic. If the color is
yellow, it means fermentation has taken place and is now acidic.
4. Why are the nutrient agar plates used in this experiment?
As with the rest of the experiments, the nutrient agar provides a broad growth medium.
Access Code (located on the lid of your lab kit): AC-OU2JH9B
Experiment 1- Selection and Differentiation of Body Inhabiting, Gram-Positive Bacteria
Table 4: Experiment 1 Growth
Conditions
Growth (Good or Poor)
Surface Tested Color Other
LB/Nutrie (Red or Observatio
nt Agar MSA Agar ns
Yellow)
White growth
present too.
Skin Good Good red Small Round
spores.
Same growth
as seen on the
Nose Good Good red skin but in
fewer
quantities.
Spores are
very few (2-
Countertop/Oth Poor Poor red 5).
er Nutrient agar
has a 1 large
colony.
1 small
Control poor poor red round
colony.
Post-Lab Questions
1. What substance in MSA confers selectivity? Why?
While MSA is both selective and differential, the high salt content is what makes it selective. This
environment will not allow certain bacterial cells to thrive making the plate selective to certain
, bacteria.
2. What substance makes MSA differential? Why?
MSA is differential due to its sugar source—Mannitol. This opens the window to a few more
bacteria making the plate differential too.
3. What purpose does phenol red serve in MSA?
The phenol is a pH level indicator. If the color is red, it is the bacteria is basic. If the color is
yellow, it means fermentation has taken place and is now acidic.
4. Why are the nutrient agar plates used in this experiment?
As with the rest of the experiments, the nutrient agar provides a broad growth medium.
