BIOLOGY Experiment 1- Selection and Differentiation of Body Inhabiting, Gram-Positive Bacteria

Student Name:
Access Code (located on the lid of your lab kit):


“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/Nutrient (Red or Yellow)” Observations”
“MSA Agar”
Agar”
Nutrient foggy,
Cover all of the
“Skin” Good Good clear. MSA
medium
yellowish green

MSA: yellowish,
white Dots on MSA.
“Nose” Good Good Nutrient: Clear None of the
but is slightly nutrient plate.
foggy.
Both whiteish Growth was
“Countertop/Other” Good Good
color similar on both.
MSA: colonies
Nutrient: clear
“Control” Good Good grew on the
MSA: yellowish
control side.




“Post-Lab Questions”
“1. What substance in MSA confers selectivity? Why?”
High sodium chloride concentration gives selectivity to MSA. This is because the sodium chloride makes
it difficult for bacteria to grow. Typically, the sodium chloride concentration is 7.5% since most bacteria
cannot live in high salinity.
“2. What substance makes MSA differential? Why?”
Mannitol is fermented by staph aureus which helps differentiate it from other Staph species.
“3. What purpose does phenol red serve in MSA?”
Phenol serves as a pH indicator.
“4. Why are the nutrient agar plates used in this experiment?”
Nutrient agar plate provides the necessary nutrients or organic carbon for the bacteria to grow.
“Insert photo of your cultures after incubation with your name clearly visible in the background:”