Baird-Parker Agar Base

Intended Use

Baird-Parker Agar Base is used with EY (Egg Yolk) Tellurite Enrichment in the preparation of Egg-Tellurite-Glycerine-Pyruvate Agar (ETGPA) for selective isolation and enumeration of coagulase-positive staphylococci from food, skin, soil, air and other materials. It may also be used for identification of staphylococci on the basis of their ability to clear egg yolk.

Summary and Explanation

A number of culture media had been utilized for the recovery of staphylococci from foods prior to the development of a new formulation by Baird-Parker in 1962.1,2 This scientist subsequently published additional results on the efficacy of the medium for the recovery of coagulase-positive staphylococci. 3,4 In 1971, Tardio and Baer5 and Baer6 reported on the results of a study comparing 18 staphylococcal isolation media in which they concluded that Baird-Parker Agar should be substituted for Vogel and Johnson Agar in the official AOAC procedure for the isolation and enumeration of Staphylococcus aureus. In this study, it was shown that Baird-Parker Agar was less inhibitory than Vogel and Johnson Agar for selected strains of S. aureus and that it possesses a diagnostic aid (egg yolk reaction) not present in Vogel and Johnson Agar. The use of Baird-Parker Agar subsequently was officially adopted by AOAC International.7

Principles of the Procedure

Baird-Parker Agar Base contains peptone, beef extract and yeast extract as sources of nitrogenous compounds, carbon, sulfur, vitamins and trace minerals. Sodium pyruvate is incorporated in order to stimulate the growth of S. aureus without destroying the selectivity. The tellurite additive is toxic to egg yolkclearing strains other than S. aureus and imparts a black color to the colonies. The egg yolk additive, in addition to being an enrichment, aids in the identification process by demonstrating lecithinase activity (egg yolk reaction). Glycine and lithium chloride have inhibitory action for organisms other
than S. aureus.

Formula

Baird-Parker Agar Base
Approximate Formula* Per 950 mL
Pancreatic Digest of Casein........................................ 10.0 g
Beef Extract................................................................5.0 g
Yeast Extract.............................................................. 1.0 g
Glycine......................................................................12.0 g
Sodium Pyruvate........................................................10.0 g
Lithium Chloride......................................................... 5.0 g
Agar.........................................................................20.0 g

EY Tellurite Enrichment
Egg yolk emulsion containing potassium tellurite consists of 30% egg yolk suspension with 0.15% potassium tellurite.
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 63 g of the powder in 950 mL of purified water. Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes.
4. Cool to 45-50°C and aseptically add 50 mL of EY Tellurite Enrichment. Mix thoroughly but gently.
5. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

Food samples are macerated in suitable broth medium, diluted as desired and the dilutions spread-inoculated onto the agar surfaces, which should be dry when inoculated. Incubate plates aerobically for 24 hours at 35 ± 2°C. Consult references for detailed instructions.7

Expected Results

Typical colonies of S. aureus are black, shiny, convex and surrounded by clear zones (egg yolk reaction) of approximately 2-5 mm. Coagulase-negative staphylococci generally do not grow well; if some growth occurs, the typical clear zones are absent. The majority of other organisms are inhibited but some may grow sparsely, producing white to brown colonies with no clearing of the egg yolk.

Limitation of the Procedure

Baird-Parker Agar is selective for coagulase-positive staphylococci, but other bacteria may grow. Microscopic examination and biochemical tests will differentiate coagulase-positive staphylococci from other organisms.

User Quality Control

Identity Specifications
Baird-Parker Agar Base
Dehydrated Appearance:        Light tan, free-flowing, homogeneous.
Solution:                              6.3 g/95 mL solution, soluble in purified water upon boiling. Solution is
                                          light to medium amber, very slightly to slightly opalescent.
Prepared Appearance (Final): Yellow, opaque.
Reaction of 6.3 g/95 mL
Solution at 25°C:                  pH 6.9 ± 0.1
EY Tellurite Enrichment
Appearance:                        Canary yellow, opaque suspension with a resuspendable precipitate.

Cultural Response
Baird-Parker Agar Base with EY Tellurite Enrichment
Prepare the medium per label directions. Inoculate and incubate at 35 ± 2°C for 24-50 hours.

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