BIO 171 MODULE 4 REVIEW
ASSESSMENT TEST WITH ALL
SOLUTIONS
What is another name for a liquid growth media, and what are the basic components? -
correct answer- Growth media in a liquid form is often referred to as nutrient broth. As
the name implies its composition consists primarily of essential 'ingredients' such as a
rich source of sugars, amino acids and vitamins. Together, a nutrient broth provides the
microbe with a source of carbon/energy, which, in turn, encourages its expansion.
What is selective media? - correct answer- Selective media allows for only the growth
of certain microbes while restricting the growth of all others
What is differential media - correct answer- Differential media is used to distinguish
between two (or more) related microbes.
Is media distinguish two often related microbes. Ex: E. Coli and salmonella. They can
grow up in a differential media but only E. Coli would react to lactose and become red
colored while salmonella will stay white/tan in color.
What are the requirements of a fastidious microbe? - correct answer- 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.
What is agar? - correct answer- In its simplest form agar is liquid growth media that
has had a hardening agent added to it. Agar is created when a polysaccharide derived
from seaweed (algae) extract is added to growth media. Agar is used to create a solid,
smooth surface on which microbes can grow.
True or False: LB agar is classified as a non-selective, differential media - correct
answer- LB agar is both a non-selective and non-differential media. LB agar is often
, used to expand unknown microbial population because it encourages microbial growth
due to the presence of universal nutrients (non-differential) and absence of restrictive
factors (non-selective).
What are the three forms of hemolysis found on blood agar plates? - correct answer-
Alpha (green), Beta (clear zones) and Gamma (white/tan). Microbes capable of alpha
hemolysis present with greenish-brown color colonies due to the incomplete (partial)
lysis of red blood cells. Beta hemolysis is classified as the capacity of a microbe to
completely lyse red blood cells. The resulting lysis presents as a distinct zone of
clearing around the growing colony. Gamma hemolysis designates the absence or lack
of hemolytic activity and the resulting colonies are often white/tan in color growing on
the red background color of the unaffected blood agar plate.
What is the primary purpose of Columbia CNA agar? - correct answer- As it
suppresses the growth of Gram-negative bacteria CNA agar is, therefore, used for
isolation of Gram-positive microbes.
Name the type of plate derived from BAP that contains lysed red blood cells. - correct
answer- Lysed red blood cells (RBCs) are a primary component in the formulation of
Chocolate agar.
Define the selective and differential abilities of a MacConkey agar plate. - correct
answer- MacConkey agar is selective in that only Gram-negative microbes will grow on
the agar—Gram-positive microbes simply do not grow. MacConkey agar is also
considered a differential media as it distinguishes between microbes capable of
fermenting lactose (red colonies) and those that are non-fermenters (white/tan
colonies).
What colors would you expect to see on an EMB plate containing E. coli? - correct
answer- The EMB plate itself is red in color while in the presence of E coli, the growing
colonies will take on a distinctive metallic green sheen.
Note: You are responsible for knowing the color and general properties (selective vs
differential) of all of the agar plates described within this module, with a special
emphasis on how a particular agar plate aids in identifying select microbes.
What is the name of the process of spreading a bacterial culture onto a petri dish? -
correct answer- Plating. Plating microbes can be done using a sterile loop, a sterile
swab, or a sterilized wire loop. Each device is simply a means of spreading the bacteria,
most commonly in a simple back-and-forth motion, across the plate.
What is the primary advantage of plating a bacterial culture as opposed to having it
grow in solution? - correct answer- The primary advantage of plating a bacterial sample
onto agar is that cells are held in place. Unlike in a nutrient broth where bacterial cells
can multiply but are free to move around in solution, bacteria plated onto agar are fixed
in such a way as to support the formation and visualization of colonies.
ASSESSMENT TEST WITH ALL
SOLUTIONS
What is another name for a liquid growth media, and what are the basic components? -
correct answer- Growth media in a liquid form is often referred to as nutrient broth. As
the name implies its composition consists primarily of essential 'ingredients' such as a
rich source of sugars, amino acids and vitamins. Together, a nutrient broth provides the
microbe with a source of carbon/energy, which, in turn, encourages its expansion.
What is selective media? - correct answer- Selective media allows for only the growth
of certain microbes while restricting the growth of all others
What is differential media - correct answer- Differential media is used to distinguish
between two (or more) related microbes.
Is media distinguish two often related microbes. Ex: E. Coli and salmonella. They can
grow up in a differential media but only E. Coli would react to lactose and become red
colored while salmonella will stay white/tan in color.
What are the requirements of a fastidious microbe? - correct answer- 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.
What is agar? - correct answer- In its simplest form agar is liquid growth media that
has had a hardening agent added to it. Agar is created when a polysaccharide derived
from seaweed (algae) extract is added to growth media. Agar is used to create a solid,
smooth surface on which microbes can grow.
True or False: LB agar is classified as a non-selective, differential media - correct
answer- LB agar is both a non-selective and non-differential media. LB agar is often
, used to expand unknown microbial population because it encourages microbial growth
due to the presence of universal nutrients (non-differential) and absence of restrictive
factors (non-selective).
What are the three forms of hemolysis found on blood agar plates? - correct answer-
Alpha (green), Beta (clear zones) and Gamma (white/tan). Microbes capable of alpha
hemolysis present with greenish-brown color colonies due to the incomplete (partial)
lysis of red blood cells. Beta hemolysis is classified as the capacity of a microbe to
completely lyse red blood cells. The resulting lysis presents as a distinct zone of
clearing around the growing colony. Gamma hemolysis designates the absence or lack
of hemolytic activity and the resulting colonies are often white/tan in color growing on
the red background color of the unaffected blood agar plate.
What is the primary purpose of Columbia CNA agar? - correct answer- As it
suppresses the growth of Gram-negative bacteria CNA agar is, therefore, used for
isolation of Gram-positive microbes.
Name the type of plate derived from BAP that contains lysed red blood cells. - correct
answer- Lysed red blood cells (RBCs) are a primary component in the formulation of
Chocolate agar.
Define the selective and differential abilities of a MacConkey agar plate. - correct
answer- MacConkey agar is selective in that only Gram-negative microbes will grow on
the agar—Gram-positive microbes simply do not grow. MacConkey agar is also
considered a differential media as it distinguishes between microbes capable of
fermenting lactose (red colonies) and those that are non-fermenters (white/tan
colonies).
What colors would you expect to see on an EMB plate containing E. coli? - correct
answer- The EMB plate itself is red in color while in the presence of E coli, the growing
colonies will take on a distinctive metallic green sheen.
Note: You are responsible for knowing the color and general properties (selective vs
differential) of all of the agar plates described within this module, with a special
emphasis on how a particular agar plate aids in identifying select microbes.
What is the name of the process of spreading a bacterial culture onto a petri dish? -
correct answer- Plating. Plating microbes can be done using a sterile loop, a sterile
swab, or a sterilized wire loop. Each device is simply a means of spreading the bacteria,
most commonly in a simple back-and-forth motion, across the plate.
What is the primary advantage of plating a bacterial culture as opposed to having it
grow in solution? - correct answer- The primary advantage of plating a bacterial sample
onto agar is that cells are held in place. Unlike in a nutrient broth where bacterial cells
can multiply but are free to move around in solution, bacteria plated onto agar are fixed
in such a way as to support the formation and visualization of colonies.
