Exercise 7: chemically defined, complex, selective, and differential media

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What do selective media allow you to do?

isolate certain bacteria even if they constitute only a small percentage of the population

What kinds of organisms does EMB agar differentiate?

lactose fermentors vs non-fermentors

Definition: selective medium

medium formulated to permit the growth of certain bacteria but not others

Definition: differential medium

medium permitting certain organisms to be distinguished from others by the appearance of their colonies

Which organisms that you tested do not required any growth factors

organisms that can grow on glucose salts

Definition: fastidious

organisms that require many complex nutritional supplements

What type of medium is trypticase soy agar?

rich, complex medium

What are complex media often called?

rick (enriched) media

What type of medium is Eosin Methylene Blue (EMB) agar?

selective (for gram-negative) and differential media (contains sugar lactose that certain organisms ferment)

What type of medium is glucose mineral agar

simple, chemically defined medium

What is the hockey stick tool used for?

spreading bacteria on spread plates

Which organisms that you tested cannot grow on glucose mineral medium?

staphylococcus

Why do complex media tend to support the growth of bacteria better?

they contain many preformed nutrients and the organisms don't have to use energy and material to synthesize the compounds supplied in the medium

How do lactose negative organisms appear on EMB plates?

white or light pink colonies

Which organisms could grow on glucose mineral medium?

E. coli, pseudomonas, enterobactor

Definition: Glucose mineral medium

a chemically defined medium containing glucose as a carbon sources and salts such as NH4Cl and KH2PO4 for a nitrogen and phosphate source

Definition: growth factor

a compound such as a vitamin or an amino acid that is required by an organism for growth

Definition: rich (or enriched) medium

a medium, usually complex, containing many growth factors; sometimes, blood or additoinal vitamins are added to permit the growth of organisms with special requirements

Definition: chemically defined medium

a synthetic medium composed of inorganic salts and usually a carbon source such as glucose

What is the purpose of selective medium?

allow some things to grow and not others

Definition: undefined medium

also termed a complex medium; a medium in which the exact amounts of chemical components and their composition are unknown because it is made of extracts or enzymatic digests of meat, plants, or yeast

Definition: complex medium

also termed an undefined medium; a medium in which the exact amounts of chemical components and their composition are unknown because it is made of extracts or enzymatic digests of meat, plants, or yeast

Definition: Enteric

associated with the intestine

What do differential medias allow you to determine about bacterial characteristics?

characteristics such as whether or not they can ferment certain sugars

Which media are the exact amounts and kinds of large organic molecules not known?

complex (undefined) medium

How do lactose positive organisms appear on EMB plates?

dark pink or purple colonies

What is the purpose of differential medium?

determine characteristics of something growing

Which organisms could ferment lactose?

e. coli and enterobactor

Which organisms could grow on the EMB plates?

e. coli, enterobactor, pseudomonas

What type of bacteria can grow on EMB plates?

gram-negative enteric rods


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