Microbiology Portage - Module 4
Microbial Growth and Control
Expanding a given microbial population allows researchers to do what? - Answer to
detect and assess the microorganism more easily
What is Growth Media? - Answer Growth media is a liquid or solid formulated to support
microbial growth.
What does Growth Media contain? - Answer The media contains essential nutrients to
provide the microbe with a source of carbon/energy. The nutrient composition often
includes a rich source of sugars, amino acids and vitamins.
What else can Growth Media also be called? - Answer Such media can also be referred
to as a nutrient broth and is commonly used to grow microbes in a suspension.
Describe LB media - Answer Perhaps the most common nutrient broth in the lab, LB
media (lysogeny broth) is a nutritionally rich liquid known for its ability to grow a vast
array of microbes.
What is Selective Media? - Answer Selective media allows for only the growth of certain
microbes and, by extension, restricts the growth of all others.
How can Selective Media be accomplished? - Answer Such an approach can be
accomplished in a variety of ways including: using limiting amounts of nutrients, varying
degrees of pH (being either very acidic or very basic media), or various chemical
additives that limit unwanted microbial growth (i.e.) antibiotics.
Describe how Selective Media works with Gram-Positive versus Gram-Negative
bacteria. - Answer If a plate is selective for Gram-Negative then it will only grow Gram-
Negative bacteria on it. It will not grow Gram-Positive bacteria on it.
What is Differential Media? - Answer Differential media distinguishes between two, often
related, microbes.
What is one way that a Differential Media can distinguish between Escherichia coli and
Salmonella? - Answer They are both Gram negative but can be distinguished by the
presence (or absence) of lactose fermentation.
If grown on the same differential media, E coli ferments lactose and turns the culture
red.
In contrast, Salmonella does not ferment lactose and the culture remains white/tan in
color.
, (This above example is probably on MacConkey agar)
What is a fastidious microorganism? - Answer an organism with complex growth
requirements such that if absent it will not grow
What are Enriched Medias used for? - Answer Enriched media is used to grow
fastidious microorganisms
Enriched Medias contain what? - Answer enriched medias contain the essential
nutrients required for the growth of this subset of microorganisms
Can a plate be a combination of selective, differential and enriched? - Answer Yes
Growth Media comes in what 2 forms? - Answer liquid and solid
What is Solid Growth Media? - Answer Solid growth media, often contained within a
sterile petri dish, is in its simplest form liquid growth media that has had a hardening
agent added.
What makes agar? - Answer The addition of a polysaccharide derived from seaweed
(algae) extract added to the liquid growth media creates a solid medium called agar.
What is a colony? - Answer As they grow, microbes form colonies that take on the
appearance of individual isolated dots.
Why does dehydrated agar (and other necessary components) get mixed with water
and heated to a high temperature? - Answer to dissolve the agar into solution. The high
temperature also ensures sterility as it will kill most, if not all, foreign microbes.
What is LB agar also known as? - Answer lysogeny broth
What color is LB agar? - Answer pale yellow
What types of microorganisms can grow on LB agar? - Answer it is a multi-purpose
media capable of growing a wide variety of microorganisms
How is LB agar classified as far as Non-Selective, Selective and Differential? - Answer
LB is classified as a non-selective and non-differential media.
LB agar is commonly used for growing what specific bacteria? - Answer E. coli
Trypticase Soy Agar is also known as what? - Answer TSA or TSAYE
What kind of media is Trypticase Soy Agar? - Answer it is another multi-purpose media
capable of growing a wide variety of microorganisms
Microbial Growth and Control
Expanding a given microbial population allows researchers to do what? - Answer to
detect and assess the microorganism more easily
What is Growth Media? - Answer Growth media is a liquid or solid formulated to support
microbial growth.
What does Growth Media contain? - Answer The media contains essential nutrients to
provide the microbe with a source of carbon/energy. The nutrient composition often
includes a rich source of sugars, amino acids and vitamins.
What else can Growth Media also be called? - Answer Such media can also be referred
to as a nutrient broth and is commonly used to grow microbes in a suspension.
Describe LB media - Answer Perhaps the most common nutrient broth in the lab, LB
media (lysogeny broth) is a nutritionally rich liquid known for its ability to grow a vast
array of microbes.
What is Selective Media? - Answer Selective media allows for only the growth of certain
microbes and, by extension, restricts the growth of all others.
How can Selective Media be accomplished? - Answer Such an approach can be
accomplished in a variety of ways including: using limiting amounts of nutrients, varying
degrees of pH (being either very acidic or very basic media), or various chemical
additives that limit unwanted microbial growth (i.e.) antibiotics.
Describe how Selective Media works with Gram-Positive versus Gram-Negative
bacteria. - Answer If a plate is selective for Gram-Negative then it will only grow Gram-
Negative bacteria on it. It will not grow Gram-Positive bacteria on it.
What is Differential Media? - Answer Differential media distinguishes between two, often
related, microbes.
What is one way that a Differential Media can distinguish between Escherichia coli and
Salmonella? - Answer They are both Gram negative but can be distinguished by the
presence (or absence) of lactose fermentation.
If grown on the same differential media, E coli ferments lactose and turns the culture
red.
In contrast, Salmonella does not ferment lactose and the culture remains white/tan in
color.
, (This above example is probably on MacConkey agar)
What is a fastidious microorganism? - Answer an organism with complex growth
requirements such that if absent it will not grow
What are Enriched Medias used for? - Answer Enriched media is used to grow
fastidious microorganisms
Enriched Medias contain what? - Answer enriched medias contain the essential
nutrients required for the growth of this subset of microorganisms
Can a plate be a combination of selective, differential and enriched? - Answer Yes
Growth Media comes in what 2 forms? - Answer liquid and solid
What is Solid Growth Media? - Answer Solid growth media, often contained within a
sterile petri dish, is in its simplest form liquid growth media that has had a hardening
agent added.
What makes agar? - Answer The addition of a polysaccharide derived from seaweed
(algae) extract added to the liquid growth media creates a solid medium called agar.
What is a colony? - Answer As they grow, microbes form colonies that take on the
appearance of individual isolated dots.
Why does dehydrated agar (and other necessary components) get mixed with water
and heated to a high temperature? - Answer to dissolve the agar into solution. The high
temperature also ensures sterility as it will kill most, if not all, foreign microbes.
What is LB agar also known as? - Answer lysogeny broth
What color is LB agar? - Answer pale yellow
What types of microorganisms can grow on LB agar? - Answer it is a multi-purpose
media capable of growing a wide variety of microorganisms
How is LB agar classified as far as Non-Selective, Selective and Differential? - Answer
LB is classified as a non-selective and non-differential media.
LB agar is commonly used for growing what specific bacteria? - Answer E. coli
Trypticase Soy Agar is also known as what? - Answer TSA or TSAYE
What kind of media is Trypticase Soy Agar? - Answer it is another multi-purpose media
capable of growing a wide variety of microorganisms
