VRBL Agar (Violet Red Bile Lactose Agar) MCQs Mock Test

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Test your expertise in coliform detection with our VRBL Agar (Violet Red Bile Lactose Agar) MCQs Mock Test! This quiz is designed for food microbiologists, lab technicians, and students to master:

Principle of VRBL Agar (bile salts, crystal violet, lactose fermentation)
Colony Identification (E. coli, Klebsiella, Enterobacter)
Regulatory Standards (ISO 4832, FDA BAM)
Troubleshooting Common Lab Issues (overgrowth, weak coloration)

🔬 Key Features:
✔ 30 Carefully Curated MCQs with detailed explanations
✔ Image-Based Questions for real-world lab scenarios
✔ Instant Scoring & Performance Analysis
✔ Mobile-Friendly Format

Perfect for certification exams (MLT, ASCP), food safety audits, and university practicals!

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Microbiology Department

VRBL Agar MCQs Mock Test

- Principle of VRBL Agar (bile salts, crystal violet, lactose fermentation)

- Colony Identification (E. coli, Klebsiella, Enterobacter)

- Regulatory Standards (ISO 4832, FDA BAM)

- Troubleshooting Common Lab Issues (overgrowth, weak coloration)

Perfect for certification exams (MLT, ASCP), food safety audits, and university practicals

Read Full Article: VRBL Agar (Violet Red Bile Lactose Agar) FAQs and MCQs

1 / 30

Category: Clinical Laboratory

What is the final pH of VRBL Agar?

8.0 ± 0.2

6.2 ± 0.2

7.4 ± 0.2

5.4 ± 0.2

2 / 30

Category: Clinical Laboratory

What is a limitation of VRBL Agar?

Supports fungal growth

Requires anaerobic incubation

May not recover stressed coliforms

Turns black with E. coli

3 / 30

Category: Clinical Laboratory

How should prepared VRBL Agar be stored?

In direct sunlight

Frozen at -20°C

At 2-8°C, protected from light

At room temperature

4 / 30

Category: Clinical Laboratory

What is the role of crystal violet in VRBL Agar?

Acts as a pH indicator

Inhibits Gram-positive bacteria

Nutrient source

Enhances lactose fermentation

5 / 30

Category: Clinical Laboratory

Which organism produces beige-pink colonies on VRBL Agar?

Enterococcus faecalis

Escherichia coli

Salmonella Typhimurium

Pseudomonas aeruginosa

6 / 30

Category: Clinical Laboratory

Which bacterium grows as pink-purple colonies with a halo on VRBL Agar?

Staphylococcus aureus

Escherichia coli

Enterococcus faecalis

Pseudomonas aeruginosa

7 / 30

Category: Clinical Laboratory

Which alternative medium can be used for stressed coliforms?

Fecal Coliform Agar (FCA)

MacConkey Agar

Blood Agar

Sabouraud Dextrose Agar

8 / 30

Category: Clinical Laboratory

Which safety precaution is necessary when handling VRBL Agar?

Use in open air

Wear gloves and lab coat

No precautions needed

Store in sunlight

9 / 30

Category: Clinical Laboratory

What confirms a true coliform in VRBL Agar testing?

Gas production in BGLB broth

Hemolysis on blood agar

Oxidase test

Catalase test

10 / 30

Category: Clinical Laboratory

What should be done if VRBL powder appears clumpy?

Discard it (likely moisture exposure)

Autoclave it

Freeze it

Use it normally

11 / 30

Category: Clinical Laboratory

Which standard method uses VRBL Agar for coliform enumeration?

FDA BAM

USP <61>

CLSI M100

ISO 4832

12 / 30

Category: Clinical Laboratory

What is the correct amount of VRBL Agar powder for 1L of water?

50.0 g

38.5–40.5 g

10.0 g

20.5 g

13 / 30

Category: Clinical Laboratory

How does bile salt selectivity work in VRBL Agar?

Inhibits Gram-negative bacteria

Promotes Gram-positive growth

Disrupts Gram-positive cell membranes

Enhances sporulation

14 / 30

Category: Clinical Laboratory

Which organism is inhibited on VRBL Agar?

Enterobacter aerogenes

Staphylococcus aureus

Klebsiella pneumoniae

Citrobacter freundii

15 / 30

Category: Clinical Laboratory

How should used VRBL plates be disposed of?

Biohazard waste (autoclave/incineration

Regular trash

Freezing

Down the sink

16 / 30

Category: Clinical Laboratory

Why should VRBL Agar NOT be autoclaved?

Heat degrades bile salts and crystal violet

It changes color

It loses lactose

It becomes too solid

17 / 30

Category: Clinical Laboratory

How long can prepared VRBL Agar be used after preparation?

4 hours

1 week

30 minutes

24 hours

18 / 30

Category: Clinical Laboratory

Which pH indicator is used in VRBL Agar?

Neutral red

Phenol red

Methyl red

Bromothymol blue

19 / 30

Category: Clinical Laboratory

VRBL Agar is commonly used to test:

Soil samples

Viral cultures

Milk and dairy products

Blood samples

20 / 30

Category: Clinical Laboratory

Why is incubation at 44°C used in VRBL testing?

To enhance fungal growth

To speed up Gram-positive growth

To kill all bacteria

To select for thermotolerant coliforms (E. coli)

21 / 30

Category: Clinical Laboratory

VRBL Agar is NOT suitable for detecting:

Yeasts and molds

Escherichia coli

Enterobacter species

Klebsiella species

22 / 30

Category: Clinical Laboratory

Which component inhibits Gram-positive bacteria in VRBL Agar?

Agar

Sodium chloride

Bile salts

Yeast extract

23 / 30

Category: Clinical Laboratory

What do non-lactose fermenters look like on VRBL Agar?

Purple colonies

Pale colonies with greenish zones

Black colonies

Shiny metallic colonies

24 / 30

Category: Clinical Laboratory

What does poor growth on VRBL Agar indicate?

Old or improperly prepared medium

Too much lactose

Incubation at wrong temperature

Both b and c

25 / 30

Category: Clinical Laboratory

At what temperature should VRBL Agar be incubated for thermotolerant coliforms?

55°C

37°C

44°C

25°C

26 / 30

Category: Clinical Laboratory

What color are lactose-fermenting colonies on VRBL Agar?

Green

Blue

Yellow

Purple/red with a halo

27 / 30

Category: Clinical Laboratory

If VRBL Agar turns yellow after preparation, what might be wrong?

Overheating during prep

All of the above

Contamination

Incorrect pH

28 / 30

Category: Clinical Laboratory

VRBL Agar is both selective and differential. What makes it selective?

Peptone content

Lactose fermentation

Neutral red indicator

Bile salts and crystal violet

29 / 30

Category: Clinical Laboratory

Which sugar is fermented by coliforms in VRBL Agar?

Mannitol

Lactose

Glucose

Sucrose

30 / 30

Category: Clinical Laboratory

What is the primary purpose of VRBL Agar?

Detect lactose-fermenting bacteria (coliforms

Culture viruses

Identify Gram-positive cocci

Isolate fungi

Your score is

The average score is 71%

Read Full Article: VRBL Agar (Violet Red Bile Lactose Agar) FAQs and MCQs

“VRBL agar colony morphology MCQs”
“How to count coliforms on VRBL agar”
“VRBL vs. MacConkey agar sensitivity”
“FDA BAM method for dairy testing”

Possible References Used

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