Selective and Differential Media

Results seen EMB plate reasonings: Large amounts of acid Small amounts of acid No fermentation

green metallic sheen pink colorless

Describe a catalase positive test

hydrogen peroxide will bubble and can convert hydrogen peroxide to water and oxygen if positive

Describe results of TSI slant

if organisms produce an acid by product the color changes

Describe Chocolate Agar

isolates and cultivates fastidious bacteria like Neisseria and Haemophilus bacteria growth factors and rbc's encourage growth of these species

Organisms unable to ferment on the HE the three sugars look like what?

make blue to green colors and no color change in the medium

Visual Mac Conkey Agar

pink: positive and ferments lactose

Results of VP test

red color= positive

Positive vs. negative indole

red= positive

What encourages the growth of staph in msa

salt

What does HE agar contain

sodium thiosulfate and ferric iron

Eosin and Methylene Blue

these are dyes which INHIBIT the growth of most Gram positive bacteria. They also react with any acidic products resulted from lactose fermentation to color the colonies.

What do coagulase positive tests do? ex

they clump; staph aureus

Methyl red results

yellow to red color change

Fermentation of mannitol produces what color and give an example of what bacteria does this

yellow, staph aureus

How does the HE agar look if the organism ferments ?

yellow/orange colonies

How is the Hektoen Enteric Agar both selective and differential

D: distinguishes between the ability of species to ferment the sugars lactose, sucrose and salicin, and the ability of species to reduce sulfur organisms that can do all three produce and acid by product S: contains dyes and bile salts that inhibit the growth of g+ bacteria

What does Mac Conkey agar distinguish among

Enterobacteriales

Describe EMB Agar plate

Eosin methylene blue agar (EMB) is both a selective and differential medium used for the detection and isolation of Gram-negative intestinal pathogens.

Examples of bacteria that ferment lactose

Escherichia coli : produce small, dark colonies with a green metallic sheen

gram postive

In MacConkey agar the bile salts and crystal red inhibit what

lactose fermenters

In MacConkey agar..it differentiates for?

hemolysins

In the Blood agar test...you are looking to see if your bacteria produces what?

gram positive

In the EMB test, eosin Y and methylene blue inhibit what?

red

In the MR test, what color is a positive result?

staphylococcus (spp.)

In the MSA test, it contains 7.5% NaCl which selects for what type of bacteria?

differential

In the MSA test, it contains Mannitol which differentiates between S. aureus and S. Epi, making it what type of media?

S. aureus that ferments mannitol

In the MSA test.....the bright yellow growth on this plate is a positive result for what?

pH indicator

In the MSA test...it contains phenol red which acts as a ____________ and turns yellow at a low pH

staphylococcus other than s. aureus

In the MSA test...the pink growth is positive for what?

beta hemolysis streptococcus pyogenes and staph aureus

In the blood agar test, complete destruction of RBCs and hb is what result? give ex

gamma hemolysis

In the blood agar test, no hemolysis is what result?

Alpha hemolysis strep pneumoniae

In the blood agar test...a green sheen is considered what? give ex

IMViC staands for what

Indole, Methyl-Red, Voges-Proskauer, Citrate

What reagent used in indole test?

Kovac's reagent

Why is mannitol salt agar considered a selective as well as a differential medium?

MSA is selective because it contains 7.5% salt-a high salt concentration that promotes the growth of some organisms while discouraging the growth of others. MSA is a differential medium because it contains the sugar mannitol and the pH indicator phenol red.

Examples of differential media types

Mac Conkey (MCK) agar, Eosin Methylene Blue (EMB) agar and MSA

Gram negative

MacConkey agar is selective for

Describe Mac Conkey agar

MacConkey's Agar is both a selective and differential media; it is selective for Gram negative bacteria and can differentiate those bacteria that have the ability to ferment lactose.

isolate

Phenylethel alcohol agar is used to _________ staph and strep

difference between selective and differential media

Selective media allows for the growth of specific organisms, while differential media is used to distinguish one organism from another.

MSA distinguishes between what genera of bacteria

Staphylococci

gram positive

The Hekoten Enteric Agar bile salts inhibit what?

enterics(Salmonella and Shigella)

The Hektoen enteric agar differentiates for?

How does the process of the TSI work

- medium is prepared as a slant with a deep bottom(butt) which is inoculated by stabbing (anaerobic environment) and then the slant itself(aerobic)

How does the TSI detect gas production and what does a black precipitate mean

- some anaerobic organisms may life the but of the slant or crack the agar surface - a black precipitate forms when H2S combines with ferric iron when organisms cannot use the sulfur as a source of an electron receptor

gram negative

What does the EMB test select for?

mixed acid fermenation

What does the MR test for?

neutral fermenation products

What does the VP test or

Gram positive

What is the Phenylethyl alcohol agar test selective for?

EMB test

What test is being performed here?

MSA (Mannitol Salt Agar)

What test is being performed here?

enteric

What type of bacteria does the EMB test differentiate for?

selective, differential

What type of media (2 types) is the Eosin Methylene Blue agar?

What organisms are catalase positive

aerobes and facultative anaerobes do this due to the ETC

What reagents are in the V-P test

alpha naphthol and KOH

What causes the appearance of red or pink colonies in Mac Conkey agar

bacteria such as Escherichia coli, Enterobacter and Klebsiella will produce acid in the medium, which lowers the pH of the agar below 6.8 and results in the appearance of red or pink colonies

Results of citrate test

blue media

How is gas production seen in durham tubes?

bubbles are formed due to fermentation

Organisms that ferment that carb. in the durham tubes does what?

changes from pink to yellow

Citrate test

differential based on ability of an organism to use citrate as its sole carbon source

Methyl-Red test

differential based on glucose fermentation by means of mixed-acid fermentation (glucose and buffer)

Describe the Oxidase test. what is it used to detect

differential between microbes that can and cannot produce the enzyme oxidase; aerobes and facultative anaerobes make Add tetramethyl-p purple : oxidase positive

What type of test is the catalase test

differential between organisms that can and cannot produce the enzyme catalase

Carbohydrate broths with Durham Tubes are differential or selective

differential for the ability to ferment a variety of carbohydrates (lactose, sucrose, or glucose) and a pH indicator

How do you interpret TSI Slants

differential test used to distinguish among enterobacteriales order of bacteria based on ability to ferment glucose, lactose, or sucrose

Describe the coagulase test

differential test used to distinguish between organisms that can and cannot make the enzyme coagulase

Indole test

differential used to distinguish between microbes that can and cannot digest the amino acid tryptophan using tryptophanase

Voges-Proskauer

distinguishes between organisms that can and cannot ferment glucose to acetone

What does the coagulase test detect

distinguishes between staph aureus and other staph species

How does MSA differentiate

distinguishes between the ability to ferment mannitol

What does IMViC series distinguish among

enterobacteriales

Bile Esculin Agar distinguishes between what species

enterococci has bile that inhibits the growth of g+ species (Selective) distinguishes between the ability of an organism to hydrolyze esculin(differential) -----> makes brown color if it hydrolyzes esculin