Portage Learning Microbiology Exam
4 Questions And Answers
/. True or False: Growth media is best suited for distinguishing between two similar
species of bacteria. - Answer-✅False. Growth media is designed to simply support (and
not restrict) microbial growth
/.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: - Answer-✅.
Differential media distinguishes between two, often related, microbes.
/.What are the requirements of a fastidious microbe? - Answer-✅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.
/.True or False: LB agar is classified as a selective, non-differential media - Answer-
✅False. LB agar is the most basic type of agar and like LB media supports the growth of
virtually all microbes without restriction
/.What is agar used for in microbiology? - Answer-✅Agar is used to create a solid,
smooth surface on which microbes can grow.
/.Match the following hemolytic class with its description of activity.
A. No hemolytic activity
B. Incomplete hemolytic
C. Complete hemolytic activity
1. Alpha hemolysis
2. Beta hemolysis
3. Gamma hemolysis - Answer-✅1 B
2C
3A
/.Columbia CNA agar is most closely related to which media:
A. Trypticase Soy Agar
B. MacConkey Agar
C. Blood agar
, D. EMB agar - Answer-✅C. CNA agar is similar to BAP as it is also enriched with blood
and allows for differentiation based on hemolytic patterns.
/.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? - Answer-✅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.
/.. 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? - Answer-✅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 (acidic conditions;
non-pathogenic) can be differentiated from non-fermenters (neutral to basic conditions;
pathogenic).
/.. In Eosin Methylene Blue (EMB) agar, what color indicates the presence of E. coli? -
Answer-✅Metallic Green.
/.Which type of agar media is best suited to support the growth of Staphylococcus?
A. MacConkey agar
B. Blood agar
C. Columbia CNA agar
D. Mannitol salt agar
E. Chocolate agar. - Answer-✅D
/.True or False: Chocolate agar gets its brown color from cocoa to produce an enriched
media. - Answer-✅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.
/.What is the process of spreading a bacterial culture onto a petri dish? - Answer-
✅Plating
/.Describe the primary advantage of using a petri dish over growing a liquid culture? -
Answer-✅The primary advantage is that cells are held into place. When grown in a
nutrient broth, bacterial cells can multiply but are free to move around in solution. When
grown on agar within a petri dish the fixed in such as way as to form colonies
/.True or False: The visualization of colonies on a petri dish represents bacterial cells
that have multiplied ~2-3 times. - Answer-✅False. When an individual colony is visible
on agar the bacterial cell has multiplied often a million times over.
4 Questions And Answers
/. True or False: Growth media is best suited for distinguishing between two similar
species of bacteria. - Answer-✅False. Growth media is designed to simply support (and
not restrict) microbial growth
/.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: - Answer-✅.
Differential media distinguishes between two, often related, microbes.
/.What are the requirements of a fastidious microbe? - Answer-✅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.
/.True or False: LB agar is classified as a selective, non-differential media - Answer-
✅False. LB agar is the most basic type of agar and like LB media supports the growth of
virtually all microbes without restriction
/.What is agar used for in microbiology? - Answer-✅Agar is used to create a solid,
smooth surface on which microbes can grow.
/.Match the following hemolytic class with its description of activity.
A. No hemolytic activity
B. Incomplete hemolytic
C. Complete hemolytic activity
1. Alpha hemolysis
2. Beta hemolysis
3. Gamma hemolysis - Answer-✅1 B
2C
3A
/.Columbia CNA agar is most closely related to which media:
A. Trypticase Soy Agar
B. MacConkey Agar
C. Blood agar
, D. EMB agar - Answer-✅C. CNA agar is similar to BAP as it is also enriched with blood
and allows for differentiation based on hemolytic patterns.
/.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? - Answer-✅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.
/.. 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? - Answer-✅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 (acidic conditions;
non-pathogenic) can be differentiated from non-fermenters (neutral to basic conditions;
pathogenic).
/.. In Eosin Methylene Blue (EMB) agar, what color indicates the presence of E. coli? -
Answer-✅Metallic Green.
/.Which type of agar media is best suited to support the growth of Staphylococcus?
A. MacConkey agar
B. Blood agar
C. Columbia CNA agar
D. Mannitol salt agar
E. Chocolate agar. - Answer-✅D
/.True or False: Chocolate agar gets its brown color from cocoa to produce an enriched
media. - Answer-✅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.
/.What is the process of spreading a bacterial culture onto a petri dish? - Answer-
✅Plating
/.Describe the primary advantage of using a petri dish over growing a liquid culture? -
Answer-✅The primary advantage is that cells are held into place. When grown in a
nutrient broth, bacterial cells can multiply but are free to move around in solution. When
grown on agar within a petri dish the fixed in such as way as to form colonies
/.True or False: The visualization of colonies on a petri dish represents bacterial cells
that have multiplied ~2-3 times. - Answer-✅False. When an individual colony is visible
on agar the bacterial cell has multiplied often a million times over.
