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 butt...no 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
- What are beta hemolytic organisms?
- S. pyogenes, GBS.
- What are some alpha hemolytic bugs?
- S. pneumoniae
- 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.
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