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MCB-L > Agar, Agar, And More Agar!!! > Flashcards

Agar, Agar, And More Agar!!! Flashcards

1
Q

Amino Acid (structure)

A

3 Parts: Carboxyl group, amino group, and “R” side chain

NH3-AA-COOH
I
R

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2
Q

Decarboxylation

A

Removal of the COOH group (carboxyl group) to COO- (releases CO2)

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3
Q

Deamination

A

Removal of NH3+ group (amino group)

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4
Q

Lysine

A

an essential amino acid

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5
Q

Agar slants

A

Agar which has hardened on a slant

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6
Q

Sensitivity

A

detects small amounts of the chemical or organism

failure leads to false NEGATIVE

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7
Q

Specificity

A

discriminates between chemical or organism in question

failure leads to false POSITIVE

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8
Q

Selective media

A

Suppresses growth of unwanted bacteria and encourages growth of desired microbes

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9
Q

Differential media

A

Facilitates distinguishing desired microbe from others in a mixed sample

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10
Q

Enterobacteriaceae

A

Found in human GI tracr

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11
Q

Enterics

A

General term for enterobacteriaceae

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12
Q

Fecal coliforms

A

bacterial indicator of sanitary quality of food and water

generally are lactose fermenters

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13
Q

Examples of enteric lactose fermenters

A

E. coli, Enterobacter, and Klebsiella

these are LESS pathogenic

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14
Q

Examples of non-lactose fermenters

A

Salmonella, Shigella, Proteus

these are MORE pathogenic

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15
Q

Lactose

A

disaccharide composed of glucose and galactose

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16
Q

End products of lactose fermentation…

A

Increase the acidity and make the pH indicator change color

17
Q

Types of agar used to identify gram (-) microbes

A

Eosin Methylene Blue (EMB) Agar
Hektoen Enteric (HE/SS) Agar

18
Q

Eosin-Methylene Blue (EMB) Agar

A

both selective and differential

selective: eosin and methylene blue dyes suppress growth of gram (+) bacteria

differential: differentiates between vigorous LFs, moderate LFs, and non-LFs

19
Q

Method for EMB differentiation

A

Lactose provides the sugar substrate for fermentation (increases acidity of media)

Eosin Y and methylene blue produce a dark purple complex with a green metallic sheen under acidic conditions

20
Q

Eosin-Methylene Blue (EMB) Agar Results

A

Gram (+) will not grow on this media

VIGOROUS LFs (like E. coli) grow dark purple with a green metallic sheen

SLOW LFs grow pink colonies

NON-LFs grow colorless colonies

21
Q

Hektoen Enteric (SS) Agar

A

both selective (for gram negative) and differential

differentiates among enterics; isolates those that can reduce sulcus to hydrogen sulfide gas (H2S)

22
Q

How is Hektoen Enteric (SS) Agar Selective

A

Bile salts inhibit growth of gram (+) bacteria

23
Q

How is Hektoen Enteric (SS) Agar Differential?

A

Differentiates between H2S producers and non-producers

Lactose provides sugar substrate for fermentation

Sodium thiosulfate is the sultry source

Ferric ammonium citrate provides a source of iron and reacts with H2S to form a black precipitate

24
Q

Hektoen Enteric (SS) Agar Results

A

Gram (+) will not grow on this media

H2S (hydrogen sulfide) producers grow black colonies or blue/green colonies with a black center

Lactose fermenters with NO H2S (like E. coli & Klebsiella pneumoniae) grow yellow to salmon pink colonies

Non-LFs (like Salmonella & Shigella) grow blue/green colonies

25
Q

Lysine Iron Agar (LIA)

A

DIFFERENTIAL media that separates gram (-) enteric bacteria upon their ability to decarboxylate and delaminate the amino acid lysine

26
Q

Contents of Lysine Iron Agar (LIA)

A

Lysine - sodium thiosulfate

0.1% glucose

27
Q

Results for Lysine Iron Agar (LIA)

A

Enterobacteriaceae

Lysine decarboxylase positive (K/K) - purple slant/purple butt

Lysine deaminase positive (R/A) - red slant/yellow butt

Black precipitate - H2S production (K/K, H2S); must be deaminated to observe black precipitate

28
Q

Lysine Iron Agar (LIA) differentiation

A

differentiates between Salmonella and Shigella - only Salmonella is an H2S producer (black precipitate)

29
Q

LIA Interpretation of purple slant/purple butt (K/K)

A

Lysine deaminase negative; Lysine decarboxylase positive

30
Q

LIA interpretation of purple slant/yellow butt (K/A)

A

Lysine deaminase negative; Lysine decarboxylase negative; Glucose fermentation

31
Q

LIA interpretation of red slant/yellow butt (R/A)

A

Lysine deaminase POSITIVE; Lysine decarboxylase negative; Glucose fermentation

32
Q

LIA interpretation of black precipitate (H2S)

A

Sulfur reduction

33
Q

Reaction type of LACTOSE FERMENTER

A

EMB: dark purple with green metallic sheen

SS: pink (or yellow)

34
Q

Reaction type of of NON-LACTOSE FERMENTER

A

EMB- colorless

SS- blue-green or colorless

MCB-L (12 decks)

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