Plate Count Agar w/ Tween 80 and Lecithin (Standard Methods Agar w/ Tween 80 and Lecithin)

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M302
For sanitary examination of surfaces, that is, for counts before and after application of disinfectants.


Plate Count Agar with Tween 80 and Lecithin is used for sanitary examination of surfaces, that is, for counts before and after application of disinfectants.

Composition**

Ingredients Gms / Litre
Casein enzymic hydrolysate 5.000
Yeast extract 2.500
Dextrose 1.000
Lecithin 0.700
Polysorbate 80 (Tween 80) 5.000
Agar 15.000

Final pH ( at 25°C) 7.0±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 29.2 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Mix well and pour into sterile Petri plates.

Principle And Interpretation

Standard Methods Agar with Tween 80 and Lecithin is formulated as per APHA (1) for the enumeration of microorganisms from flat and nonporous surfaces. For the purpose of this medium the plates should be prepared carefully to ensure the presence of meniscus of agar extending above the top of the poured plate.

Casein enzymic hydrolysate provides amino acids while yeast extract supplies vitamin B complex and dextrose gives energy to microorganisms. Polysorbate 80 and lecithin act as neutralizers to inactivate the residual disinfectants where the samples are collected (2, 3). Lecithin inactivates quaternary ammonium compounds whereas polysorbate 80 neutralizes formalin, phenolic disinfectants, hexachlorophene etc.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Gelling: Firm, comparable with 1.5% Agar gel

Colour and Clarity of prepared medium: Light yellow coloured clear to slightly opalescent gel forms in Petri plates

Reaction: Reaction of 2.92% w/v aqueous solution at 25°C. pH : 7.0±0.2

pH: 6.80-7.20

Cultural Response: M302: Cultural characteristics observed after an incubation at 35-37°C for 24-48 hours.

Organism Inoculum (CFU) Growth Recovery
Escherichia coli ATCC 25922 50-100 luxuriant >=70%
Staphylococcus aureus ATCC 25923 50-100 luxuriant >=70%

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.

Reference

  1. Richardson S. D. (Ed.), 1985, Standard Methods for the Examination of Dairy Products, 15th ed., APHA, Washington, D.C.
  2. Erlandson A. L. and Lawrence C. A., 1953, Science, 118:274.
  3. Brummer B., 1976, Appl. Environ. Microbiol., 32:80.
More Information
Product Name Plate Count Agar w/ Tween 80 and Lecithin (Standard Methods Agar w/ Tween 80 and Lecithin)
SKU M302
Product Type Regular
Physical Form Powder
Origin Animal
Packaging type HDPE
References 1. Levine M., 1918, J. Infect. Dis., 23:43.
2.Levine M., 1921, Bull. 62, Iowa State College Engr. Exp. Station.
3.Greenberg A. E., Trussell R. R. and Clesceri L. S. (Eds.), 1998, Standard Met for the Examination of Water and Wastewater,20th ed., APHA, Washington, D.C.
4.Marshall R. (Ed.), 1992, Standard Methods for the Examination of Dairy ,, Products, 16th ed., APHA Inc., New York.
5.Downes F. P and Ito K. (Ed.), 2001, Compendium of Methods for the Microbiological Examination of Foods, 4th ed., APHA,Washington, D.C.
6.Howard B. J., 1994, Clinical and Pathogenic Microbiology, 2nd Ed., Mosby Year Book, Inc
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