Med Micro Lab Exam 2 Prep

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Pos result for TCBS

growth, yellow colonies

Pos result for Quad ID

growth

Pos result for MTM Chocolate

growth

Pos result for Nitrate Reduction

Initially red or remains colorless after addition of zinc

Pos result for Urease

Pink

Pos result for Citrate

Blue

Pos result for selective aspect of MacConkey

growth

Pos result for differential aspect of MacConkey

red-pink colonies

Pos result for TSI slant (slant)

yellow slant

Pos result for TSI slant (butt)

yellow or yellow/black butt

Pos result for TSI slant (gas formation)

cracked agar or gas bubbles

Pos result for Gelatin

liquid

Strong Pos result for EMB

growth, metallic green colonies

Weak Pos result for EMB

growth, purple colonies

Pos result for String test

string between loop and slide

Pos result for SIM deep (sulfur)

black

Pos result for SIM deep (indole)

red ring (after addition of Kovac’s reagent)

Pos result for SIM deep (motility)

growth beyond stab line

Pos result for Durham tube (fermentation)

yellow

Pos result for Durham tube (gas)

bubble within the Durham tube

Pos result for Decarboxylase (fermentation)

yellow

How does the TCBS test work?

Increased salt, bile salts inhibit Gram +

How does Quad ID test work? (i.e., name components of each quad)

• Q1: NAD

• Q1: NAD + Hemin

• Q3: Hemin

• Q4: 5% horse blood

How does MTM Chocolate test work? (4 components inhibiting …)

• Vancomycin inhibits Gram +

• Colistin inhibits Gram -

• Nystatin inhibits yeast

• Trimehoprim inhibits swarming Proteus

How does Nitrate Reduction test work?

Nitrate reductase reduces nitrate to nitrite, and zinc forces nitrate to nitrite

How does Urease test work?

Urease converts urea to ammonia, which raises pH. Increased pH causes color change (due to phenol red indicator).

How does Citrate test work? (i.e., what question is being asked)

Can bacteria use citrate as a carbon source? pH indicator is bromothymol blue, and the media becomes blue at alkaline/ high pH.

How does MacConkey test work? (selective)

Crystal violet and bile salts inhibit Gram +

How does MacConkey test work? (differential)

pH indicator is neutral red (<6.8 = pink and >7.0 = yellow)

How does TSI Slant test work? (slant)

Lactose/sucrose fermentation

How does TSI Slant test work? (butt)

• yellow = glucose fermentation

• yellow/black = hydrogen sulfide production

How does TSI Slant test work? (cracked agar)

Gas formation

How does Gelatin test work? (i.e., what question is being asked)

Can bacteria digest gelatin via gelatinase enzyme?

How does EMB test work? (selective)

Gram - bacteria

How does String test work? (name the component needed)

0.5% sodium deoxycholate

How does SIM deep work? (sulfur)

Hydrogen sulfide interacts with iron.

How does SIM deep work? (indole)

Medium contains tryptophan; bacteria break down tryptophan to produce indole

How does SIM deep work? (motility)

Can bacteria grow beyond the stab line where they were inoculated?

How does Durham tube test work? (3 components)

• pH indicator is phenol red

• acid production is a byproduct of fermentation

• Durham tube traps gas

How does Decarboxylase test work? (4 components)

• Ornithine or lysine in broth; can bacteria use either as a carbon source?

• Fermentation lowers pH —> yellow color

• Decarboxylation (expression of decarboxylase) raises pH —> purple

• Expression of decarboxylase breaks down ornithine / lysine

• Oil needed following inoculation to keep out oxygen & encourage bacteria to “push together”

Which microbe is TCBS test suitable for?

Vibrio

Which microbe is Quad ID test suitable for?

Haemophilus

Which microbe is MTM Chocolate test suitable for?

Neisseria

Which microbe is Nitrate Reduction test good for?

Moraxella

Which microbe is Urease test suitable for?

Gram + and Gram -

Which microbe is Citrate test suitable for?

Enterics

Which microbe is MacConkey test suitable for?

differentiate Gram -

Which microbe is TSI slant suitable for?

differentiate Enterics

Which microbe is Gelatin test suitable for?

Enterics

Which microbe is EMB test suitable for?

Enterics

Which microbe is String test suitable for?

differentiate Vibrio from Aeromonas

Which microbe is SIM deep test suitable for?

Gram - Enterics and Listeria

Which microbes are Durham tube test suitable for?

Neisseria and Enterics

Which microbe is Decarboxylase test suitable for?

Enterics

Cellular morphology of Neisseria

Gram negative diplococci

Cellular morphology of Haemophilus

Gram negative coccobacillus

Cellular morphology of Vibrio

Gram negative curved rods

Cellular morphology of Enterics

Gram negative rods

Why is the candle jar best to incubate Neisseria and Moraxella?

like low oxygen and high carbon dioxide environments

We worked with 4 BSL-2 pathogens during this unit. List them.

• Haemophilus influenzae

• Vibrio parahaemolyticus

• Proteus vulgaris

• Klebsiella pneumoniae

Regarding Haemophilus, what are X, V, and XV factors?

• X = hemin

• V = NAD

• XV = both

Vibrio are _____ positive.

oxidase

Enterics are ____ negative.

oxidase

Which pathogen is a strong lactose fermenter?

Escherichia coli

How does EMB test work? (differential)

lactose fermentation

Pos result for Decarboxylase (decarboxylation)

Purple

*Note: orange —> yellow —> purple