MicroBio LAB Practical Guide Flashcards
Gram Stain
Stains used and their purpose
Primary: Crystal violet
Iodine: Mordant; fixes primary stain
Ethanol: Decolorizer; removes the die
Safranin: Counterstain
Starch Hydrolysis
Reagent
Substrate
Enzymes required
Positive/Negative + End product
Reagent = Iodine
Enzyme: Amylase + Maltase
Substrate: Starch
Positive
If starch is hydrolyzed, CLEAR zone of hydrolysis surround growth
End product = glucose
Negative
If starch is not hydrolyzed, blue-black color
Lipid Hydrolysis
Reagent
Substrate
Enzymes required
Positive/Negative
Reagent: No reagent added
Enzyme: Lipase
Substrate: Triglycerides
Positive:
If lypolysis occurs = clear area around bacteria
If lypolytic enzymes are not present = opaque
IMViC Test: Indole
Substrate & Enzyme
Reagent
Positive/Negative
End Product
Substrate: Tryptophan
Enzyme: Tryptophanase
Reagent: Kovak’s
Positive: Red reagent Layer
Negative: Yellow reagent layer
End product: Indole
IMViC Test: Methyl Red
Substrate & Enzyme
Reagent
Positive/Negative
End Product
Substrate: Glucose
Enzyme: NONE
Reagent: Methyl Red
Positive: Red
IMViC: Voges Praskauer
Know end product for all IMViC Tests
Substrate: Glucose
Reagent: Add reagent VP-A, then VP-B
Results:
Red color = Positive
No change/Yellow = Negative
IMViC Test: Citrate Utilization Test
Substrate:
Enzyme:
Positive/Negative
End Product
Substrate: Citrate
Enzyme: Citrate permease & Citrase
Positive: If citrate utilization occurs = Blue, growth on surface
Negative: If citrate utilization doesn’t occur = green, no growth
End product: Carbon dioxide
Hydrogen Sulfide Test
End Product
Substrate: Cystein, thiosulfate
Enzyme: Cysteine desulfurase & Thiosulfate reductase
Results:
Black precipitate = positive
None = negative
Urease Test
Substrate/Enzyme
Reagent
Positive/Negative
Substrate: Urea
Enzyme: Urease
Reagent: pH Indicator
Positive: Pink
Negative: Yellow/no change
Carbohydrate Fermentation:
Lactose
Dextrose
Sucrose
Enzymes:
Lactase
Glycosidase
Sucrase
End products:
Acid, Acid & Gas, Negative
Yellow, yellow & bubble, red|pink/no chance (negative for carbohydrate fermentation)
Nitrate Reduction Test
Substrate: Nitrate (NO3)
Enzyme: Nitrate Reductase
Solution A+B: Red is +, clear is - for Nitrite
Then, Zinc: Red is -, clear is positive for NO, N2O, N2
Which media
selects and
differentiates
Staph species
MSA Agar (Mannitol Salt Agar)
Which two medias differentiates bacteria
based on whether they are
a lactose fermenter or
non lactose fermenter
EMB agar and MAC agar
Which agar do Streptococcus species grow best on?
Blood agar or enriched media
Which media partially inhibit gram negative bacteria
PEA Agar (Phenoethylalcohol Agar)
