m Plate Count Broth

Intended Use

m Plate Count Broth is used for enumerating microorganisms by membrane filtration.

Summary and Explanation

m Plate Count Broth is a nonselective general-purpose medium for determining bacterial counts from food and water samples using the membrane filtration procedure. Also known as m Tryptone Glucose Yeast Broth or m Standard Methods Broth, this medium has the same formulation as Plate Count Agar except that agar has been omitted and the ingredients are employed in twice the concentration as in the solid medium.¹

Principles of the Procedure

Yeast extract is a source of trace elements, vitamins and amino acids. Peptone provides carbon and nitrogen for bacterial metabolism. Dextrose is a fermentable carbohydrate and carbon source.

User Quality Control

Identity Specifications
m Plate Count Broth
Dehydrated Appearance: Light beige to beige, free-flowing, homogeneous.
Solution:                       1.7% solution, soluble in purified water upon
                                   warming. Solution is light to medium amber,
                                   clear to slightly opalescent, may have a very
                                   slight precipitate.
Prepared Appearance:   Light to medium amber, clear to slightly opalescent,
                                  may have a very slight precipitate.
Reaction of 1.7%
Solution at 25°C:          pH 7.0 ± 0.2
Cultural Response
m Plate Count Broth
Prepare the medium per label directions. Inoculate and incubate at 35 ± 2°C for 18-24 hours.

Formula

m Plate Count Broth
Approximate Formula* Per Liter
Yeast Extract................................................................ 5.0 g
Tryptone.................................................................... 10.0 g
Dextrose..................................................................... 2.0 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 17 g of the powder in 1 L of purified water. Mix thoroughly.
2. Warm slightly to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes.
4. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

1. Collect samples according to recommended guidelines.^1,2
2. Place a sterile absorbent pad in each 50 × 9 mm Petri dish.
3. Saturate the pad with approximately 2.0-2.4 mL of prepared medium.
4. Place an inoculated membrane filter, inoculated side up, on the saturated pad.
5. Incubate in a 35 ± 2°C incubator for 18-24 hours.

Expected Results

After incubation, count the colonies on the surface of the filter. The colonies can be subcultured to appropriate media for identification, if desired.

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