Metabolic Activities Flashcards
Starch digestion
- Tests for amylase
- Amylase turns starch into sugars
- Iodine turns stach black, but not sugar
- Reagent: Iodine
Starch digestion positive
Clearing around streak
Starch digestion negative
Entire plate is black - no clearing
Milk Agar Plate
- Casein digestion
- Tests for caseinase
- Caseinase converts casein into amino acids
- No reagent
Milk Agar Positive
Clearing around streak
Milk Agar Negative
No clearing around streak
TSA Plate
- Catalase
- Oxidase Production
Catalase
- TSA Plate
- Tests for presence of catalase
- Reagent: H2O2
- Catalase converts H202 to water and oxygen gas
Catalase Positive
Bubbles after adding peroxide
Catalase Negative
No bubbles after adding peroxide
Oxidase Production
- TSA Plate
- Tests for presence of cytochrome oxidase
- Cytochrome oxidase is last enzyme in ETS
- Reagent: on swab
Oxidase Production Positive
Dark Purple (pink = weak positive) on swab
Oxidase Production Negative
No color change on swab
SIM Media
- H2S Production
- Indole Production
H2S Production
- SIM Media
- Tests for cysteine desulfurase
- Cysteine desulfurase converts cysteine into pyruvate by removing H2S
- Reagent: iron in medium
H2S Production Positive
Black precipitate
H2S Production Negative
No black precipitate
Indole Production
- SIM Media
- Tests for tryptophanase
- Tryptophanase converts tryptophan into indole
- Reagent: Kovac’s reagent
Indole Production Positive
Red layer on tope of broth
Indole Production Negative
No color change
Citrate Utilization
- Tests for ability to use citrate as a carbon source
- No other carbon source (sugar) available in medium
- Reagent: ammonium ions and brom thymol blue in medium (pH indicator)
Citrate Utilization Positive
Bacteria will grow
Usually turns deep blue color
Citrate Utilization Negative
Bacteria do not grow
No color change
(However bacteria may grow without changing color)
Urea Broth
- Tests for urease
- Urease converts urea into ammonia
- Reagent: Phenol red in medium
Urea Broth Positive
Cerise or hot pink
Urea Broth Negative
Any color besides cerise or hot pink
Nitrate Broth
- Tests for nitrate reductase
- Nitrate reductase converts nitrate into nitrite
- Reagent: Nitrate 1 (Sulfanilic acid) and Nitrate 2 (dimethyl-a-napthalamine)
- Secondary reagent Zinc (to confirm negative)
Nitrate Broth Positive
-Red color after adding reagents
OR
-No color change, then add zinc > still no color change
Nitrate Broth Negative
No color change, then red after adding zinc
Nitrate Broth Explanation
Sometimes instead of converting Nitrate to Nitrite nitrate reductase converts it to “something else,” so there is no color change to red (no nitrite present). However nitrate reductase is still present.
To confirm a negative, add zinc to tube. Zn reacts with nitrate to produce a red color. If NR was present, there will be no color change after adding zinc because the nitrate was converted to “something else”
MRVP Broth
- Methyl Red
- Voges-Proskauer
Methyl Red
- Tests for dextrose fermentation
- Reagent: methyl red
Methyl Red Positive
Red color
Methyl Red Negative
No red color
Voges-Proskauer
- Tests for Butanediol fermentation
- Reagent: Barritt’s Solution A (a-naphtol) and B (KOH)
Voges-Proskauer Positive
Pink to red color
Voges-Proskauer Negative
No pink or red
Fermentation Tests
- Tests for specific enzymes that can ferment each sugar
- Dextrose
- Sucrose
- Mannitol
- Lactose
- Reagent: Phenol Red
- Durham Tube to collect gas
Durham Tube
Upside down tube in test tube
Collects gas created during rxn
Fermentation Test Possible Results
+ acid + gas
+ acid - gas
- acid - gas
Fermentation Test Positive
Acid: Yellow
Gas: Bubble in Durham tube
Fermentation Test Negative
Acid: Red (does not turn yellow)
Gas: No bubble in Durham tube
IMVC Tests
Indole Production
Methyl Red
Voges-Proskauer
Citrate Utilization
-Used to differentiate between E. coli and E. aerogenes (very morphologically similar)
-E. coli is positive for I and M, negative for V and C
-E aerogenes is opposite
