Portage Learning BIOD 171 Module 4
Exam Module 4
1. True or False: Growth media is best suited for distinguishing
between two similar species of bacteria.
False. Growth media is designed to simply support (and not restrict)
microbial growth.
2. A researcher is asked to determine which of two vials contains E coli
and which contains Salmonella. Knowing both are Gram-Negative
while only one of them is capable of fermenting lactose, which type
of media would be best suited:
A. Growth media
B. Differential media
C. Selective media
D. Selective and Differential media
B. Differential media distinguishes between two, often related,
microbes.
3. What are the requirements of a fastidious microbe?
A fastidious microbe is an organism with complex growth
requirements such that if absent it will not grow. Enriched medias
thus contain these specific and essential nutrients required for the
growth of a particular subset of microorganisms.
4. True or False: LB agar is classified as a selective, non-differential
media.
False. LB agar is the most basic type of agar and like LB media
supports the growth of virtually all microbes without restriction.
5. What is agar used for in microbiology?
Agar is used to create a solid, smooth surface on which microbes
can grow.
6. Match the following hemolytic class with its description of activity.
1. Alpha hemolysis
B A. No hemolytic activity
, 2. Beta hemolysis
C B. Incomplete hemolytic activity
3. Gamma hemolysis
A C. Complete hemolytic activity
7. Columbia CNA agar is most closely related to which media:
A. Trypticase Soy Agar
B. MacConkey Agar
C. Blood agar
D. EMB agar
C. CNA agar is similar to BAP as it is also enriched with blood and
allows for differentiation based on hemolytic patterns.
8. True or False: Chocolate agar gets its brown color from cocoa to
produce an enriched media.
False. Chocolate (cocoa) is never added to the media. The name is
derived simply based on the color that actually comes from the
presence of ‘cooked’ (lysed) red blood cells in the media.
9. A researcher is studying a strain of E. coli currently growing on a
MacConkey plate. However, the researcher can’t remember if E. coli
is Gram-Positive or Gram-Negative. Would a Gram stain be
necessary to confirm? Why or why not?
No. A Gram stain would not be necessary, as only Gram-Negative
microbes will grow on MacConkey agar. Thus, E. coli is a Gram-
Negative microbe.
10. In an attempt to detect the presence of the pathogenic strain of
E. coli O157:H7, a researcher spread a culture onto a MacConkey
agar with failed results. What type of agar should they (correctly)
try next? Why?
The microbe should be plated on SMAC (Sorbitol-MacConkey agar)
as it is specifically formulated to detect O157:H7. Pathogenic E. coli
(O157:H7) cannot ferment sorbitol while non-pathogenic E. coli can
ferment both soribitol and lactose. Therefore, colonies that ferment
Exam Module 4
1. True or False: Growth media is best suited for distinguishing
between two similar species of bacteria.
False. Growth media is designed to simply support (and not restrict)
microbial growth.
2. A researcher is asked to determine which of two vials contains E coli
and which contains Salmonella. Knowing both are Gram-Negative
while only one of them is capable of fermenting lactose, which type
of media would be best suited:
A. Growth media
B. Differential media
C. Selective media
D. Selective and Differential media
B. Differential media distinguishes between two, often related,
microbes.
3. What are the requirements of a fastidious microbe?
A fastidious microbe is an organism with complex growth
requirements such that if absent it will not grow. Enriched medias
thus contain these specific and essential nutrients required for the
growth of a particular subset of microorganisms.
4. True or False: LB agar is classified as a selective, non-differential
media.
False. LB agar is the most basic type of agar and like LB media
supports the growth of virtually all microbes without restriction.
5. What is agar used for in microbiology?
Agar is used to create a solid, smooth surface on which microbes
can grow.
6. Match the following hemolytic class with its description of activity.
1. Alpha hemolysis
B A. No hemolytic activity
, 2. Beta hemolysis
C B. Incomplete hemolytic activity
3. Gamma hemolysis
A C. Complete hemolytic activity
7. Columbia CNA agar is most closely related to which media:
A. Trypticase Soy Agar
B. MacConkey Agar
C. Blood agar
D. EMB agar
C. CNA agar is similar to BAP as it is also enriched with blood and
allows for differentiation based on hemolytic patterns.
8. True or False: Chocolate agar gets its brown color from cocoa to
produce an enriched media.
False. Chocolate (cocoa) is never added to the media. The name is
derived simply based on the color that actually comes from the
presence of ‘cooked’ (lysed) red blood cells in the media.
9. A researcher is studying a strain of E. coli currently growing on a
MacConkey plate. However, the researcher can’t remember if E. coli
is Gram-Positive or Gram-Negative. Would a Gram stain be
necessary to confirm? Why or why not?
No. A Gram stain would not be necessary, as only Gram-Negative
microbes will grow on MacConkey agar. Thus, E. coli is a Gram-
Negative microbe.
10. In an attempt to detect the presence of the pathogenic strain of
E. coli O157:H7, a researcher spread a culture onto a MacConkey
agar with failed results. What type of agar should they (correctly)
try next? Why?
The microbe should be plated on SMAC (Sorbitol-MacConkey agar)
as it is specifically formulated to detect O157:H7. Pathogenic E. coli
(O157:H7) cannot ferment sorbitol while non-pathogenic E. coli can
ferment both soribitol and lactose. Therefore, colonies that ferment
