Coliforms

Coliform

Gram Negative Bacteria
Media VRBA

Outline:
Presumptive by VRBA
Confirmatory Test by BGLB

Procedure
Do a serial dilution of concentration 10E-2, 10E-3, 10E-4
Do a Spread Plate on VRBA
Do 3 replications fro Each Dilution
Incubate 35˚C, 24 Hrs
Do a colony count (positive’ll be purple red colony, >0.5mm)
Select 3 representative colony an inoculate into BGLB for confirmation
Incubate 35˚C 24hrs
If all the tube are positive (with gases), then above colony count is valid
If only a fraction is valid, take (fraction of positive tube X colony count)

Violet Red Bile Agar

Bile salts suppresses gram positive and non Enterobacteriaceae family members
Lactose differentiates lactose fermentors and non-lactose fermentors. Lactic acid will cause a decrease in pH, Neutral Red indicator will then turn red giving a red colony

Lauryl Sulphate Tryptose Broth (LST)
· Lactose differentiates Lactose fermentors and non ferementors
· Lauryl Sulphate suppresses non-coliform growthTryptose and NaCl provides the right osmopressure for Coliform to ferment