VRBA (MUG), MPN, Membrane Filter, Petrifilm - Food Safety Analytics Laboratory (FSA Lab)

VRBA (MUG), MPN, Membrane Filtration, and Petrifilm

Method	Principle	Target Organisms	Application
VRBA (MUG)	Selective agar with bile salts, lactose, and MUG; detects β-glucuronidase activity via fluorescence	Coliforms, E. coli	Dairy, food, water; confirmatory for E. coli
MPN (Most Probable Number)	Statistical estimation using serial dilutions and gas production in broth	Coliforms, E. coli	Water, shellfish, low-count foods
Membrane Filtration	Filtration of sample through 0.45 µm membrane, incubation on selective media	Coliforms, E. coli, fecal coliforms	Bottled water, juices, environmental samples
Petrifilm™ (3M)	Dry rehydratable film with chromogenic substrates and gelling agents	Coliforms, E. coli, total count	Food, dairy, surfaces; rapid enumeration

VRBA (MUG): Fluorogenic detection of E. coli via β-glucuronidase cleavage of MUG to 4-methylumbelliferone (blue-green fluorescence under UV). Inhibits Gram-positive flora using bile salts and crystal violet.
MPN: Ideal for turbid or particulate-rich samples. Time-consuming but statistically robust. Often used with LST-MUG or EC-MUG broths
Membrane Filter: Allows direct colony counting; useful for large volumes. Requires sterile technique and vacuum filtration setup.
Petrifilm™: Compact, easy-to-use alternative to agar plates. Color-coded colonies (e.g., red with gas for coliforms, blue for E. coli). AOAC-validated for many matrices.

Standard	Application
FDA BAM Chapter 4	Coliform and E. coli enumeration in foods
APHA / SMWW	Water and shellfish testing (MPN, membrane filter)
ISO 4832 / 16649-2	Coliform and E. coli detection using VRBA and chromogenic media
AOAC Official Methods	Validated Petrifilm™ protocols for dairy, meat, produce