Lab Exam 2 Microbiology

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PEA or Phenylethyl Alcohol Agar

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-Encourages growth of G+
-Inhibits growth of most G-
-Phenylethyl alcohol is selective agent that inhibits G- by breaking down their membrane permeability barrier.
-used to isolate staph and strep from specimens of bacterial.
-Screening out species such as E.coli and proteus

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Bile Esculin

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-Undefined
-Selective and differential medium
-Esculin extracted from the bark of the horse chestnut tree, a glycoside composed of glusoce and esculetin
-Bile is selective agent to separate streptococcus bovis group and enterococci from from other streptococci.
-Ferric citrate is added as a source of oxidized iron to to indicate a positive test

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Bile Esculin: selective agent

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Bile;separate streptococcus bovis group and enterococci from from other streptococci

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Mannitol Salt

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-Used for isolation and differentiation of s. aureus
-S. aureus ferments the manitol causing pH to lower making the hte Phenol red turn yellow

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Mannitol Salt: No growth

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Organism is inhibited by NaCl and not a staphylococcus

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Mannitol salt: good growth

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Organism not inhibited by NaCl
most likely a staphylococcus

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Mannitol salt: Yellow growth

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Mannitol is fermented most likely S. aureus

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Bile Esculin: Medium darkened after 48 hrs

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possible member of group D streptococcus or Enterococcus
-Ferric citrate forms the darkeness

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Bile Esculin: Medium not darkened after 48 hrs

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presumptively not member of group D streptococcus or Enterococcus

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Poor growth on Phenylethyl alcohol

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Organism is inhibited by Phenylethyl alcohol and is probably a Gram negative

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MacConkey agar

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Bile salts and CV inhibit growth of G (+) bacteria. Neutral red dye is the indicator.
Differentiates based on ability to ferment lactose.

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MacConkey agar: NG

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G(+) inhibited by bile or CV

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MacConkey agar: good growth

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Gram negative NOT inhibited by bile or CV

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MacConkey agar: pink to red growth

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organism produces acid from lactose fermentation
probale coliform

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Eosin Methylene Blue agar (EMB)

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Contains pepton, lactose, sucrose, and dyes eosin Y and methylene blue.
Sugars encourage growth and help differentiate along with dyes.
Lactose supports coliforms such as E. coli
sucrose supports pathogens such as Proteus or salmonella.
Purpose of dye:
1. Inhibit growth of G +
2.Reaction with different fermenters

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Eosin Methylene Blue agar (EMB): NG

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Organism inhibited by methylene blue and is G+

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Eosin Mehtylen Blue agar (EMB) : Pink/red Growth

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Organism ferments lactose with little acid production. possible coliform

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Eosin Mehtylen Blue agar (EMB)
Growth is "dark"

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Organism ferments lactose and sucrose with acid production. Possible coliform

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Eosin Mehtylen Blue agar (EMB): Colorless growth

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Organism does not feremnt lactose or sucrose NR. noncoliform

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Hektoen agar

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designed to isolate salmonella and shigella species form other enterics

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HE: poor growth or no growth

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Organism inhibited by bile and/or one of the dyes included. Gram positive

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HE: good growth

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Organism not inhibited by any dyes included. gram negative

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HE: Pink to orange growth

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Organism produces acid from lactose fermentation Not shiglella or Salmonella

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HE blue green growth with black ppt

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Organsim does not ferment lactose, but reduces sulfur to hydrogen sulfide (H2S) possible salmonella

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HE Blue green growth without black ppt

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organsim does not ferment lactose or reduce sulfur. No reaction. possible Shigella or Salmonella

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Xylose Lyxine Desoxycholate XLD

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Used to isolate and identify shigella and providencia from stool samples

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XLD poor growth

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inhibited by desoxycholate, G+

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XLD: Good growth

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organism is not inhibited by desoxycholate, G-

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XLD: Growth is yellow

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Organism produces acid from xylose fermentation (A) Not Shigella or Providencia

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XLD: red growth with balck center

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Organism redues sulfur to H2S, Not shigella or providencia (probable Salmonella)

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XLD red growth without black center

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Organism does not ferment xylose or xylose slowly; alkaline products from lyzine Probable shigella or providencia

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Phenol red broth

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Used to differentiate between members of enterobactariacae and to distinguish them from other G- rods

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MR VP

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Used to distinguish between members of the family Enterbacteriacae and and to distinguish them from other G- rods

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Mixed acid fermentation

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overcomes the phosphate buffer in the medium and lowers the pH

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VP test

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Adding VP reagents to the medium oxidezes the acetoin to diacetyl which in turn reacts with guanidine nuclei fro peptone to produce a red color

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MR VP: Methyl red result: Red

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Red means mixed acid fermentation (pH below 4.4)

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VP test

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2, 3 butanediol fermentation (acetion produced)

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Calalase test

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used to ID organism that produce enzyme catalase. Most commonly used to differentiate members of micrococcaccae from the catalase-negative streptococcaacie

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Catalase test what to look for

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bubbles no bubbles

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Oxidase

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This test is used to identify bacteria containing the respiratory enzyme cytochrome c oxidase

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Chromogenic reducing agent

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chemicals that develop as they become oxidized

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Oxidase test: Dark blue

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Cytochrome c oxidase is presnt

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Ntirate test

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Virtually all members of enterobacteriaceae perform a one-step reduction of nitrate to nitrite. The nitrate test differentiates them form gram-negative rods that either do not reduce nitrate or reduce it beyond nitrite to N2 or other compounds

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Nitrate reductase

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enzyme that helps bacteria perform a single-step reduction of nitrate to nitrite.

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Denitrification

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bacteria that are capable of enzymatically converting nitrate to molecular nitrogen

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Citrate permease

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can transport the molecules into the cell and enzymaticaly convert it to pyruvate

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Citrate test

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used to determine the ability of an organism to use citrate as its sole source of carbon.

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Phenylalanine test

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used to differentiate the genera morganella, proteus, and providencia from other members of enterobacteriaceae

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Phenylalanine test: green color

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Phenylalanine deaminase present

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Phenylalanine test: no color change

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Phenylalanine deaminase not present

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Starch hydrolysis

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tests for presence or absence of amylase...look for clearing

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Urease

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differentiate organisms based on there ability to hydrolyze urea with the enzyme urease. Urinary tract pathogens form the genus proteus may be distinguished from other eneric bacteria by their rapid urease activity

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Urease broth: pink

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Rapid urea hydrolysis; strong urease production

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protein found in milk

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casein

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TSIA

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used to differentiate members of of enterobactariacae and to distinguish them from other gram negative rods such as pseudomonas aeruginosa

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TSIA All yellow

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glucose and lactose and/or sucrose rementation with acid accumulation in slant and butt

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TSIARed slant yellow butt

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Glucose fermentation with acid production. Proteins catabolized aerobically (in the slant) with alkaline products (reversion)

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TSIA All red

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No fermentation. peptone catabolized aerobically and anaerobicallywith alkaine products. Not from enterobacteriaceae

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TSIA Red slant/no change in the butt

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No fermentation. Peptone catabolized aerobically with alkaline products. Not from enterobacteriaceae

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TSIA no change anywhere

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Slow grower, not from enterobacteriaceae

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TSIA: black ppt in agar

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Sulfur reduction