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Lab practical #2
Terms in this set (77)
Define mycolic acid
a waxy substance that gives acid-fast cells a higher affinity for the primary stain and resistance to decolorization by an acid alcohol solution.
Why is the acid fast stain called acid fast?
Because it means that acid cannot decolorize them because the walls contain mycolic acid which repels typical aqueous stains.
What is the application of 3.8
the acid-fast stain is a differential stain used to detect cells capable of retaining a primary stain when treated with an acid alcohol. Important because it's used to identify bacteria in the genus Mycobacterium, some of which are pathogens.
What was the primary stain in the acid fast stain?
What was the decolorizer in the acid fast stain?
What was the counterstain in the acid fast stain?
TB Methylene Blue
What is the genus of bacteria that the acid fast stain is used on?
What are two significant diseases caused by the Mycobacterium genus?
Leprosy and Tuberculosis
Define pure culture
a microbial culture consisting of only one species
Define mixed culture
a microbial culture consisting of two or more species.
What is the application of 1.4 (Streak Plate Method)
The identification process of an unknown microbe relies on obtaining a pure culture of that organism. The streak plate method produces individual colonies on an agar plate. A portion of an isolated colony then may be transferred to a sterile medium to start a pure culture.
What is the application of 2.2-2.4
Recognizing different bacterial growth morphologies on agar plates is a useful step in the identification process.
a visible mass of cells
very convex elevation
an elevation that is raised in the center
not transparent or translucent; impenetrable to light, not allowing light to enter.
allowing light, but not detailed images to pass through
showing varying colors as an opal does
showing luminous colors that seem to change when seen from different angles.
to shine by reflection with a sparkling luster
Agar slants have two practical uses. What are they?
Media for cultivation and maintenance of stock cultures.
Define filiform growth
dense and opaque with a smooth edge
a type of surface membrane produced by organisms that float on top of the medium
a type of surface membrane that sinks to the bottom.
a type of surface membrane that appears to clump.
metabolic process by which an organic molecule acts as an electron donor and one or more of its organic products act as the final electron acceptor.
Define differential media
a growth medium in which different species of microorganisms can be distinguished usually.
What if the pH indicator used in the Phenol Red broth tubes?
Phenol Red is yellow below pH _____ in phenol red broth
Phenol Red is pink above pH _____ in phenol red broth
What would cause a PR tube to turn yellow?
acid production and low pH
What would cause a PR tube to turn pink?
Ammonia and high pH
What is the function of a Durham tube?
to indicate gas production
What is the application of the PR broth test 5.3?
PR broth is used to differentiate members of Enterobacteriaceae and to distinguish them from other Gram negative rods
What three carbohydrates did we use?
Dextrose, Sucrose and Lactose
a process in which a molecule is split into two parts through the interaction of H+ and (OH)- of a water molecule.
Define extracellular enzyme
enzymes secreted from the organism to catalyze reactions outside the cell.
Define intracellular enzyme
enzymes that catalyzes it's reaction inside the cell.
Starch is made up of small units of
List the two forms of starch
linear (amylose) and branched (amylopectin)
Starch is broken down by enzymes into
List the two enzymes that hydrolyze starch
alpha-amylase and oligo-1,6-glucosidase
What reagent is added to the starch plate to test for hydrolytic enzymes?
a product of decarboxylation of certain amino acids
What is the name of the buffer used in the Urea hydrolysis broth
What is the function of the Urea hydrolysis buffer?
Used to resist alkalinization of the medium from peptone metabolism
What is the pH indicator in the Urea hydrolysis broth?
What color indicated below 8.4 in Urea hydrolysis
Urea is hydrolyzed by the enzyme urease into
2NH3 and CO2
What is the source of nutrient in the urease broth?
A trace (0.0001%) of yeast extract
What is the application of the urease test?
Used to differentiate organisms based on their ability to hydrolyze urea with the enzyme urease. Urinary tract pathogens from the genus Proteus may be distinguished from other enteric bacteria by their rapid urease activity.
Why would a positive test turn pink?
Because it would mean that a rapid urease-positive organism was present.
Define combination differential media
combine components of several compatible tests into one medium, thus saving critical diagnostic time and money
What three activities are detected by SIM media?
sulfur reduction, indole production from tryptophan, and motility
__________ in the agar of SIM media provide amino acids
Animal tissue and casein
What two enzymes reduce sulfur to hydrogen sulfide
Cysteine desulfurase and thiosulfate reductase
Cysteine is hydrolyzed by the enzyme Cysteine desulfurase into
H2S, ammonia, and pyruvate
What is added to the media to detect Hydrogen sulfide?
Iron, in the form of ferrous ammonium sulfate, to form ferric sulfide, a black precipitate
How is ferric sulfide produced?
When iron combines with Ferrous ammonium sulfate
Tryptophan is hydrolyzed by tryptophanase into
pyruvate, ammonia, and indole
What is the name of the reagent added to the SIM media to detect indole?
What is the application for the SIM test?
Used to identify bacteria that are capable of producing indole, using the enzyme tryptophanase. Used to differentiate sulfur-reducing members of enterobacteriaceae, especially members of the genera Salmonella, Francisella, and Proteus from the negative Morganelli morganii and Providencia retgeri. Used to detect motility as well.
How do you inoculate the SIM test tube?
With an inoculating needle (Stab inoculation).
An acid fast positive cell will be
An acid fast negative cell will be
blue or green
Application of starch hydrolysis (5.12)
Used to isolate and presumptively identify Gardnerell vaginalis, aids in differentiating members of the genera Corynebacterium, Clostridium, Bacillus, Bacteoides, Fusobacterium, and Enterococcus, most of which have + and - species.
Clearing around growth =
amylase is present (+)
No clearing around growth=
no amylase is present (-)
Pink Urease tube=
rapid urea hydrolysis; strong urease production (+)
no urea hydrolysis; urease is absent (-)
Black in the medium=
sulfur reduction (+)
no black in the medium=
sulfur is not reduced (-)
Growth radiating outward from stab line=
No radiating growth=
Red in the alcohol layer of Kovac's reagent=
Tryptophan is broken down into indole and pyruvate (+)
Reagent color is unchanged=
Tryptophan is not broken down into indole and pyruvate (-)
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