Glossary of Micro lab

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Calculate # of viable bacteria/mL
(# colonies/volume plated) x (reciprocal of dilution)
What is MacConkey selective for?
Inhibits G+ bacteria...i.e. selects for G-
What is MacConkey differential for?
Lactose fermenters produce pink colonies.
What is Mannitol salt selective for?
Organisms that can withstand high salt
What is mannitol salt differential for?
Bacteria that ferment mannitol produce yellow-orange colonies (S. aureus).
What does TSI tell us?
*Ability to ferment glucose, lactose, sucrose
*ability to produce gas
*ability to produce H2S
What is K/A?
Alkaline slant, acid butt - glc fermentation; no lactose fermentation.
What does K/K mean?
Alkaline slant, alkaline CHO fermentation.
What does A/A mean?
Ferments lactose and sucrose
What does black mean (on TSI)?
The bacterium produces H2S which forms a complex with iron.
Example of Lac+ aerobe in stool sample.
E. coli, enterobacter, Klebsiella
Example of Lac- aerobe from stool.
Proteus, Psuedomonas, Salmonella, Shigella
Stool organism that grows on SBA anaerobically at 35 degrees C.
Stool organism that grows on SBA anaerobically at 48 degrees C.
What stains acid-fast?
How does acid-fast work?
Sample is stained with basic fuchsin; decolorized with acid-alcohol; counterstained with methylene blue.
What are the 3 classifications of hemolysis on SBA and how do they look?
Alpha: partial w/green tint
Beta: total
Gamma: none
What are beta hemolytic organisms?
S. pyogenes, GBS.
What are some alpha hemolytic bugs?
S. pneumoniae
S. mitis
What is a gamma hemolytic organism?
What is the main test to differentiate between Staph and Strep?
Staph are catalase+
Strep are catalase-
How is a catalase test done?
Specimen mixed with H2O2.
Positive = vigorous bubbling
What does coagulase differentiate between?
Staph Aureus - coagulase+
S. epidermidis - coagulase-
How is a coagulase test done?
Mix with plasma.
Positive: clumps form
Negative: no clumps
What will P disk tell us?
(This is the optochin disk)
Strep pneumoniae will be sensitive.
Strep mitis will be resistant.
What will the A disk tell us?
(This is the bacitracin disk)
Strep. pyogenes will be sensitive.
GBS will be resistant.
What is the oxidase test?
What do results look like?
Tests for presence of oxidase
Place reagent on paper; add specimen.
Positive turns blue/purple within 10 seconds.
What are some oxidase positive bugs?
Neisseria sp.
Moraxella catarrhalis

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