M4S • Microbiology for StudentsDigital Learning Chapter

Microbiology • Culture Media • Digital Learning Chapter

Violet Red Bile Agar (VRBA)

Violet Red Bile Agar interactive microbiology learning & laboratory system

7 ChaptersM4SStudent NotesLaboratory Media

Contents

1. Intended Use 2. Principle 3. Reagents & Preparation 4. Laboratory Procedure 5. Quality Control 6. Limitations 7. References

0 of 7 chapters opened0%

📚 Intended Use

Selective and differential isolation of coliforms in water, food, milk, and dairy products. The supplied source describes the medium in relation to detection of lactose-fermenting Gram-negative bacteria.

Learning focus: VRBA combines selective inhibition with differential detection of lactose fermentation.

📖 Principle

The supplied formulation uses nutritional components together with selective agents and a pH indicator.

• Gelatin peptone → nutrients
• Yeast extract → vitamins
• Lactose → energy source
• Bile salts + crystal violet → inhibit Gram-positive bacteria
• Neutral red → indicator

Differentiation

🧫 Reagents & Media Preparation

Formulation supplied in the source

Component	Amount
Lactose	10 g
Gelatin Peptone	7 g
Sodium Chloride	5 g
Yeast Extract	3 g
Bile Salts	1.5 g
Neutral Red	30 mg
Crystal Violet	2 mg
Agar	15 g
Demineralized Water	1000.0 mL
pH	7.4 ± 0.2 @ 25°C

Source note: The supplied text states that pH is adjusted as required to meet performance standards.

Preparation

1. Suspend 41.5 g in 1000 mL water.
2. Heat to boiling; the supplied source specifically states do not autoclave.
3. Mix and pour plates.

🔬 Laboratory Procedure & Interactive Observation

Procedure

1. Inoculate sample.
2. Incubate for 18–24 hours at 33–37°C.
3. Observe colony morphology.

Colony Observation Simulator

Select an observed colony pattern to display the interpretation given in the supplied source.

Interpretation from source: Pink/red colonies indicate lactose fermentation; colorless colonies indicate non-lactose fermentation; inhibition/no growth is associated with organisms inhibited by the medium.

🧪 Quality Control

Organism	Expected result in supplied source
Escherichia coli ATCC® 25922	Red colonies with red zone
Salmonella enterica serovar Typhimurium ATCC® 14028	Colorless colonies
Enterococcus faecalis ATCC® 29212	Inhibition

QC learning point: The source uses reference strains to illustrate expected colony appearance or inhibition.

⚠️ Limitations

• Medium should not be stored for more than one day.
• For laboratory use only; not for direct diagnosis.

📚 References

1. Dahlberg, A.C., H.S. Adams, and M.E. Held. 1953. Sanitary Milk Control. Pub. 250. National Academy of Sciences, Washington, D.C.
2. Druce, R.G., N.B. Bebbington, K. Elson, J.M. Harcombe, and S.B. Thomas. 1957. Journal of Applied Bacteriology 20:1–10.
3. Downes, F.P. and K. Ito. 2001. Compendium of Methods for the Microbiological Examination of Foods. 4th ed. APHA, Washington, D.C.
4. Food and Drug Administration. 2000. Bacteriological Analytical Manual Online. AOAC International, Gaithersburg, MD.
5. Wehr, H.M. and J.F. Frank. 2004. Standard Methods for the Examination of Dairy Products. 17th ed. APHA, Washington, D.C.
6. MacFaddin, J.F. 1985. Media for Isolation-Cultivation-Identification-Maintenance of Medical Bacteria. Vol. 1. Williams & Wilkins, Baltimore, MD.

M4S – Microbiology for Students
Violet Red Bile Agar (VRBA) • Digital Learning Chapter
Prepared from the user-supplied VRBA source content.