Violet Red Bile Agar (VRBA)

🧪 VRBA Interactive Microbiology Learning & Lab System

📚 Intended Use

Selective and differential isolation of coliforms in water, food, milk, and dairy products. Proposed by MacConkey in 1905 for detection of lactose-fermenting gram negative bacteria.

📖 Principle

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

🧫 Reagents

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 (Adjusted as required to meet performance standards)

🧪 Media Preparation

1. Suspend 41.5 g in 1000 ml water
2. Heat to boiling (DO NOT autoclave)
3. Mix and pour plates

🔬 Procedure

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

🧫 Colony Observation

🧪 Quality Control

Organism	Result
Escherichia coli ATCC® 25922	Red colonies with red zone
Salmonella enterica serovar Typhimurium ATCC® 14028	Colorless colonies
Enterococcus faecalis ATCC® 29212	Inhibition

⚠️ Limitations

• Medium should not be stored for more than one day
• For laboratory use only (not 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. J. Appl. Bacteriol. 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.