Microbiology Lab Quiz 4

What is the Simmons Citrate Agar differential for

To determine if an organism can use citrate as its sole carbon source

Is Simmons Citrate Agar differential

Yes; uses citrate

How is Simmons Citrate Agar made

Inoculate the slant with a light inoculum without stabbing then incubate

What is a positive result for Simmons Citrate Agar

A blue color change indicates citrate-permease production

What is a negative result for Simmons Citrate Agar

No growth and medium remains green

Is visible growth required for Simmons Citrate Agar

No

What is the purpose of TSI Agar

To differentiate members of the family “Enterbacteriaccae” based on the fermentation of glucose/lactose/sucrose and sulfur to H2S reduction

Is TSI Agar selective

No

Is TSI Agar differential

Yes

How is TSI Agar used

Stab the butt and streak the slant then incubate

What does yellow slant and yellow butt indicate in TSI

Glucose and one other sugar (lactose/sucrose fermentation)

What does red slant and yellow butt indicate in TSI

Only glucose fermentation

What does red slant and red butt indicate in TSI

Used peptones; No fermentation

What does black precipitate indicate in TSI

H2S production

What do lifts or cracks indicate in TSI

Gas production

Is visible growth required for TSI Agar

Yes

What is the purpose of the Motility Test Medium

To determine bacterial motility

Is Motility Test Medium selective

No

Is Motility Test Medium differential

Yes

How is Motility Test Medium used

Stab straight down and incubate

What is a positive result for Motility Test Medium

Diffuse cloudy growth away from stab line

What is a negative result for Motility Test Medium

Growth only along stab line

How to interpret Motility Test Medium results

Positive is motile, negative is non-motile

Is visible growth required for Motility Test Medium

Yes

What is the purpose of Nutrient Gelatin

To determine gelatinase production

Is Nutrient Gelatin selective

No

Is Nutrient Gelatin differential

Yes

What is a positive result for Nutrient Gelatin

Medium stays liquid after refrigeration

What is a negative result for Nutrient Gelatin

Medium solidifies after refrigeration

How to interpret Nutrient Gelatin results

Positive indicates gelatinase present, negative indicates absent

Is visible growth required for Nutrient Gelatin

Yes

What is the purpose of Phenol Red Broths

To test the fermentation of specific carbohydrates

Are Phenol Red Broths selective

No

Are Phenol Red Broths differential

Yes

What is a positive result for Phenol Red Broths

Yellow color indicates acid, gas bubble in Durham tube indicates gas

What is a negative result for Phenol Red Broths

Red or orange color with no gas

How to interpret Phenol Red Broth results

Yellow is fermentation red is no fermentation

Is visible growth required for Phenol Red Broths

Yes

What is the purpose of the Methyl Red Test

identifies glucose fermentation end products to separate acid fermentation pathway

Is the Methyl Red Test selective

No

Is the Methyl Red Test differential

Yes

How is the Methyl Red Test used

Inoculate MR/VP broth incubate then add methyl red

What is a positive result for Methyl Red Test

Red color after adding methyl red

What is a negative result for Methyl Red Test

Yellow or orange color

How to interpret Methyl Red Test results

Red means mixed acid fermentation yellow means not

Is visible growth required for Methyl Red Test

yes

What is the purpose of the Voges-Proskauer Test

To detect acetoin production

Is the VP Test selective

No

Is the VP Test differential

Yes

How is the VP Test used

Inoculate MRVP broth incubate then add Barritt's reagents

What is a positive result for VP Test

Red color after adding reagents

What is a negative result for VP Test

No color change or copper color

How to interpret VP Test results

Red means acetoin present negative means absent

What is the purpose of Urea Broth

To detect urease enzyme

Is Urea Broth selective

No

Is Urea Broth differential

Yes

What is a positive result for Urea Broth

Bright pink color indicating alkaline pH

What is a negative result for Urea Broth

No color change or yellow/orange

How to interpret Urea Broth results

Pink means urease positive yellow means negative

Is visible growth required for Urea Broth

Yes

What is the purpose of Litmus Milk

To differentiate based on lactose fermentation reduction coagulation and peptonization

Is Litmus Milk selective

No

Is Litmus Milk differential

Yes

What does pink color in Litmus Milk indicate

Acid from lactose fermentation

What does blue color in Litmus Milk indicate

Alkaline from casein digestion

What does white color in Litmus Milk indicate

Litmus reduction

What does clot or curd in Litmus Milk indicate

Coagulation

What does the transparent, amber appearance in Litmus Milk indicate

Peptonization

Is visible growth required for Litmus Milk

Yes