Exercise 6: Selective and Differential Media

What do general purpose media do in terms of growth?

support the growth of a variety of microorganisms

What are examples of general purpose media?

Nutrient Agar, Tryptic Soy Agar, Brain Heart Infusion

NA=

Nutrient Agar

TSA=

Tryptic Soy Agar

BHI=

Brain Heart Infusion

In terms of growth, what do selective media do?

use inhibitors to prevent growth of certain organisms

What are examples of selective media?

Phenyl Ethyl Agar, Eosin Ethylene Blue, MacConkey Agar

PEA=

Phenyl Ethyl Agar

EMB=

Eosin Methylene Blue

In terms of growth, what do differential media do?

allow growth of many microbes, but differentiation is seen by indicators that detect changes that may have occurred

Example of differential media:

dyes, reagents, blood cells, culture conditions; includes EMB, Blood agar, and MacConkey

BA=

blood agar

What are combination media?

media that is both selective and differential

Examples of combination media:

EMB and MacConkey

MAC=

MacConkey Agar

If a selective media selects for gram positive, what will happen?

Will only grow gram +; gram - will not grow on this media

When it comes to nutrients in media, complex media means:

undefined; exact chemical composition not known

What are examples of complex media?

TSA, BHI

When it comes to nutrients in media, defined means:

known chemical composition for each component

PEA is general/selective/differential/combo?

selective

What is the inhibitor in PEA?

phenylethyl alcohol

PEA prevents what growth?

growth of gram negatives; gram positives will grow on this media

Blood agar media is general/selective/differential/combo?

differential

What is the indicator in blood agar?

red blood cells

What is BA made out of?

TSA base with 5% sheep's blood added

Blood agar is useful in differentiating:

hemolysis patterns

What are the different types of hemolysis seen in BA?

-beta

-alpha

-gamma

What is the best lysis pattern in BA?

beta

What is the worse lysis pattern in BA?

gamma

MacConkey Agar is general/selective/differential/combo?

Combo; both selective and differential

What is the indicator in MAC?

neutral red

What does neutral red do in MAC?

differentiates lactose fermenters from non-fermenters

What is the inhibitor in MAC?

crystal violet and bile salts

What does the inhibitor do in MAC?

prevents the growth of gram positives

What type of bacterium thrive on MAC?

Enterobacteriaceae; ex: E. coli

In MAC, if a organism ferments, what is the outcome?

will produce an acid--->lowers the pH---->neutral red will turn HOT PINK

In MAC, if a organism doesn't ferment, what is the outcome?

bacteria will grow--->no acid produced--->pH increases--->no pink color produced

EMB is general/selective/differential/combo?

combo

What is the inhibitor of EMB?

Eosin and methylene blue

the inhibitor in EMB prevents:

the growth of gram positives

The indicator in EMB is:

Eosin and methylene blue

What does the indicator do in EMB?

differentiate lactose fermenters from non-fermenters (gram negatives)

EMB is typically used to:

screen for coliforms

What is the color outcome for lactose fermentation in EMB?

varies depending on pathway it takes; ranges from pale pink/lavender to black

on EMB, pale pink/lavender color means:

took the 2, 3-butanediol pathway

on EMB, dark/black color means:

took the mixed acid pathway

Both the 2,3-butanediol and mixed acid pathway are positive or negative for lactose fermentation?

positive

Organisms that have flagella are:

motile

Motility can be detected by what kind of media?

motility media--->soft agar

How is motility media inoculated?

by a single stab line

How do you tell if a microbe is motile or not in motility media?

cloudiness around the stab line; non-motile organisms remain confined in the path of the stab line

What dye indicator can be used to aid in the detection of motility?

tetrazolium chloride