Types of Media – Biochemical Tests – Flashcards

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question
What are biochemical tests used for?
answer
used to determine physiological characteristsics of microorganism, particularly in terms of bacterial enzymes and chemistry of biooxidation
question
What does starch agar test for?
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amylase
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What does amylase hydrolyze?
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starch to simple sugars
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What is added to starch plate after incubation?
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iodine
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If amylase is present in starch agar, what will be observed around an amylase positive colony?
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no blue/black colour
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What does milk agar test for?
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caseinase
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What does caseinase hydrolyze?
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casein to amino acid products
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What is casein?
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a primary protein in milk that gives it its white colour
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If caseinase is present in milk agar, what will be observed around a caseinase positive colony?
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clearing
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What does a lipase plate test for?
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lipase
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What does lipase hydrolyze?
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fat to glycerol and fatty acids
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What does the production of fatty acids do to pH?
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production of fatty acids lowers pH
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When lipase is present in the lipase plate, what colour is observed around the lipase positive colony?
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dark blue precipitate
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What are sugar fermentation tubes used for?
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determining if a microorganism can ferment particular sugars
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What sugars of interest can sugar fermentation tubes contain?
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glucose, lactose, mannitol
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What are the three components of a sugar fermentation tube?
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sugars of interest, pH indicator, Durham tube
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What is the pH indicator of a sugar fermentation tube?
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phenol red
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If a microorganism is able to ferment the sugar, what will the result of the fermentation produce?
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acid
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When acid is present in a sugar fermenation tube, what colour indicates that the microorganism is positive for fermentation?
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yellow
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What is another product that some microorganisms produce during fermentation?
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gas
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How will the secondary product in sugar fermentation tubes appear in the Durham tube?
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a void or bubble
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In a sugar fermentation tube, how does an alkaline reaction occur?
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utilization of peptone in the broth and not the sugar
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If an alkaline reaction occurs, what colour will indicate this?
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darkening (red/dark red)
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What does Methyl Red (MR) test for?
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mixed acid fermentors
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What colour indicates a positive Methyl Red test?
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red
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What does Voges-Proskauer (VP) test for?
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2,3 butanediol fermentors
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What do 2,3 butanediol fermentors produce less of compared to mixed acid fermentors?
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acid
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What is actually tested for in a Voges-Proskauer (VP) instead of a butanediol producer?
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acetoin (acetyl methyl carbinol)
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What are Barrit's reagents in a VP test?
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alpha-napthol and KOH
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When oxygen is present in a VP test, what reagent reacts with the product?
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KOH
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When oxygen is present, what colour indicates that the microorganism is a 2,3 butanediol producer?
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brick red colour
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What is alpha-naphthol ultimately used for in a VP test?
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to intensify the red color
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What is an example of a MR + microorganism?
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Escherichia
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What is an example of a VP + microorganism?
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Enterobacter
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What are the products of a catalase test?
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H2O and O2
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What indicates that the microorganism is catalase positive?
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bubbles
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What does an oxidase test test for?
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oxidase
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What products does an oxidase test produce?
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coloured products
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What aromatic arene does an oxidase test use?
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dimethyl-p-phenylenediamine hydrochloride
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When oxidase is present, what colour indicates that oxidase is present?
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dark blue black
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What does nitrate test for?
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the ability of microorganisms to reduce nitrate
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What is produced in a nitrate test?
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N2 + NH3 and other products
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What is present in a nitrate broth?
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nitrates (NO3-)
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What are the reagents in the nitrate test?
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sulfanilic acid and dimethyl-alpha-naphthylamine
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What colour indicates that the microorganism is nitrate positive?
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red
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What is added to the tube in a nitrate test if it is yellow?
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zinc
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What would zinc do to a negative nitrate test?
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it will turn red
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If the broth does not turn red after the addition of zinc in a nitrate test, what is therefore said about the microorganism?
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it is true positive
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What happened to the nitrate in a true + Nitrate test?
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the nitrate broth was completely reduced to products other than NO2-
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What does a indole/tryptophan test test for?
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tryptophanase
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What does tryptophanase convert tryptophane into?
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indole and pyruvic acid
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What reagent is added to identify indole in an indole test?
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Kovac's Reagent (p-dimethylaminobenzaldehyde, amyl or butyl alcohol, and HCl)
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If indole is present, what colour indicates that the microorganism is positive for indole?
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red
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What does a urea test test for?
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urease
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What does urease convert urea into?
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ammonia and CO2
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If ammonia is present, what happens to the pH of the solution?
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increases
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If ammonia is present, what colour indicates that the microorganism is urease positive?
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red
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What does the enzyme cysteine desulfurase remove from cysteine to produce H2S?
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sulfur side chain
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When H2S is present in a cysteine test, what is produced to indicate an H2S positive test?
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black precipitate
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What does a SIM test for?
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sulfur, indole, and motility
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What does a simmons citrate test test for?
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utilizes citrate as the sole carbon source
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Other than growth, what colour will indicate a citrate positive microorganism?
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Prussian blue
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What does Phenylalanine test for?
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PPA and NH3
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What is added to PPA to indicate presence of products?
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ferric chloride
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If PPA is present, what colour will indicate a positive phenylalanine test?
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deep green
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What does litmus milk test for?
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lactose fermentation
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What kind of reaction causes a pink liquid to form due to a drop in pH from the fermentation of lactose?
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acid reaction
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What kind of reaction produces a pink solid due to to acid production and coagulation of proteins causing the solid formation?
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acid curd reaction
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What kind of reaction causes litmus to be reudced and to be colorless (tube appears white since only milk remains)?
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reduction
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What causes a blue liquid to be produced when protein breakdown produces amino acids that are deaminated and release ammonia?
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alkaline reaction
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What causes a clearing of medium (may be brown or amber) caused by the enzyme caseinase?
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peptonization/proteolysis
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What reaction causes the tube to turn white except for a small region at the top where oxygen reoxidizes the litmus to the red coloured form?
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acid curd reduction
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