BAIRD PARKER MEDIUM

 

A medium base used for the detection of coagulase-positive Staphylococci.

 

Code: CB1/1006

 

Typical formula g/l

 

Pancreatic digest of casein	10.00
Beef extract	5.00
Yeast extract	1.00
Sodium pyruvate	10.00
Glycine	12.00
Lithium chloride	5.00
Agar	15.00

         

 

Supplement with Egg Yolk Tellurite Emulsion 100 ml CBS006

 

Final pH 7.1 +/- 0.1

 

Directions

Suspend 58g in 1000 ml of cold distilled water; heat to boiling and autoclave at 121°C for 15 minutes. Cool to 50°C and, using aseptic conditions, add 50 ml of Egg Yolk Tellurite Emulsion; mix well and pour into sterile petri dishes.

 

 

Description

Baird Parker Agar Base is a selective and diagnostic medium recommended by ISO 6881 and by FDA for the isolation and enumeration of coagulase-positive staphylococci in foodstuffs. It is also recommended by USP and EP for the isolation of S.aureus in non-sterile pharmaceutical products. Lithium chloride and potassium tellurite inhibit conta­minating flora, glycine and sodium pyruvate facilitate the development of staphylococci. Some yeasts, fungi and bacilli also grow, but these are easily distinguishable by their morphology and by the grey colour of the colonies. ISO 6881 recommends the addition of 5 mg/l of sulphamezathine to the medium after sterili­sation to inhibit the development of Proteus spp.

 

In use

ISO 6881-1 recommends the following procedure: Prepare the sample suspension and further decimal dilutions with Maximum Recovery Diluent. Transfer by means of a sterile pipette 0,1 ml of the test sample if liquid or 0,1 of the initial suspension in the case of other products, to each of two agar plates. Repeat the procedure for further decimal dilutions if necessary. Carefully spread the inoculum as quickly as possible over the surface of the agar plate. Allow the plates to dry. Invert the plates and incubate them for 24 +/- 2hrs at 37°C and re-incubate for a further 24  +/- 2hrs. After incubation for 24hrs mark on the bottom of the plates the positions of any typical colonies. Re-incubate, then mark any new typical colonies.  Also mark any atypical colonies present.

Enumerate those plates that contain at maximum 300 colonies with 150 typical and/or atypical colonies at two successive dilutions. One of the plates shall contain at least 15 colonies. Select for confirmation five characteristic colonies if there are only characteristics colonies, or five non-characteristic colonies if there are only non-characteristic colonies, or five characteristic and five non-characteristic colonies if both types are present, from each plate. Typical S .aureus are black or grey, shining and convex colonies (1-1.5 mm in diameter after 24 h of incubation, 1,5-2,5 mm in diameter after 48 hours), surrounded by a zone of clea­ring of the medium. After at least 24hrs an opalescent ring immediately in contact with the colonies may appear in this clear zone.  Atypical colonies may present one of the following morphologies: Shining black colonies with or without a narrow white edge; the clear zone is absent or barely visible and the opalescent ring is absent or hardly visible.

Grey colonies free of clear zones. Bacteria belonging to genera other than Staphylococcus may grow with colonies similar to staphylococci. Microscopic examination of Gram stain will enable the distinction of other genera from staphylococci. For confirmation carry out coagulase test using Coagulase Plasma EDTA according to the procedure reported by technical sheet. Baird Parker recommends enrichment in Tryptone Soy Broth with 10% NaCl or Giolitti-Cantoni Broth to test material containing less than five staphylococci per gram. AOAC recommends a technique for coagulase-positive staphylo­cocci detection in foodstuffs, which involve enrichment in Tryptone Soy Broth with 1% Sodium Chloride for 48 hours, then a tran­sfer to Baird-Parker Medium and catalase and coagulase tests.

  

User quality assurance (37°C-48 h)

 

Productivity control

S.aureus ATCC 6538: good growth, black colonies with clear halo

S.aureus ATCC 25923: good growth, black colonies with clear halo

 

Selectivity control

E.coli ATCC 25922: inhibited

Specificity control

S.epidermidis ATCC 12222: partially inhibited, black colonies without halo

 

Storage

Dehydrated media: 15-30°C

User prepared plates: up to 24 hours at 2-8°C

 

References  

Baird-Parker, A.C. (1962) J. Appl. Bact., 25, 12-19.

Eurpean Pharmacopoeia, 3^rd ed. 2001 Supplement

ISO 6888-1. Microbiology of foods and animal feeding stuffs Horizontal method for the enumeration of coagulase positive staphylococci, part 1: technique using Baird Parker Agar Medium . 1998.

FDA (1995) Bacteriological Analytical Manual, 8^th ed. Revision A, 1998. Published by AOAC International.

U.S. Pharmacopoeia 24, NF 19 (2000)