Modified Pseudomonas Selective Agar w/ Cetrimide (Twin Pack)

Intended Use

Milk Agar with Cetrimide is recommended for detection and enumeration of Pseudomonas aeruginosa in water. It is recommended by BIS.

Composition

Formula adjusted, standardized to suit performance parameters

Directions

Suspend 19.8 grams of Part B in 250 ml of distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 20 minutes. Suspend 100 grams of Part A in 750 ml of distilled water. Sterilize by autoclaving at 15 lbs pressure (121°C) for 5 minutes. After autoclaving cool both the parts to 50°C. Aseptically add Part A solution to Part B solution, mix well and pour into sterile Petri plates.

Principle And Interpretation

Milk Agar with Cetrimide is formulated as recommended by BIS (1) for detection and enumeration of Pseudomonas aeruginosa from water. Strains of Pseudomonas aeruginosa are identified by their pigment i.e. pyocyanin production. Pseudomonas aeruginosa is the only species of Pseudomonas or gram negative rod known to excrete pyocyanin. Pseudomonas aeruginosa hydrolyzes casein and produces a yellow to green diffusible pigment. Subculture a loopful of culture medium from Asparagine Proline Broth (M1192) tubes showing either growth or fluorescence on Milk Agar plates and examine for pigment production. Peptic digest of animal tissue, yeast extract and skim milk provide nitrogen, sulphur, vitamins and other growth nutrients. Sodium chloride maintains osmotic equilibrium. Cetrimide (Cetyl trimethylammonium bromide) is a quaternary ammonium compound which inhibits a wide variety of microorganisms including Pseudomonas species other than Pseudomonas aeruginosa.

Quality Control

Appearance

• Part A: White to cream homogeneous free flowing powder
• Part B: Cream to yellow homogeneous free flowing powder

Gelling

Firm, comparable with 1.5% Agar gel

Colour and Clarity of Prepared Medium

Cream coloured opalescent gel forms in Petri plates.

Reaction

Reaction of 1.98% w/v aqueous solution of Part B at 25°C. pH: 7.3±0.2

pH

7.10-7.50

Cultural Response

M1273S: Cultural characteristics observed after an incubation at 35-37°C for 24-48 hours.

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. International Organization for Standardization (ISO), Draft ISO/DIS 83 60-1:1988