Baird Parker Agar was developed by Baird-Parker (1,2) from the Tellurite - glycine formulation of Zebovitz et al (3) for isolation of Staphylococcus aureus from foods.
This medium was found to be less inhibitory to Staphylococcus aureus than other media, at the same time being more selective (4, 5, 6). Subsequently it was officially adapted by the AOAC and is also recommended in USP for use in Microbial limit test (7). However, identity of Staphylococcus aureus isolated on Baird-Parker Agar must be confirmed with a coagulase reaction. Smith and Baird-Parker (8) found that the addition of 50 mg/l Sulphamethazine in the medium, suppresses the growth and swarming of Proteus species.
Sodium pyruvate protects injured cells and helps recovery. Lithium chloride and potassium tellurite inhibit most of the contaminating microflora except Staphylococcus aureus. Glycine, pyruvate enhances growth of Staphylococcus. With the addition of egg yolk, the medium becomes yellow, opaque. Proteolytic bacteria produce a clear zone around colony in egg yolk containing media. A clear zone and grey-black colonies on this medium are diagnostic for coagulase positive Staphylococci. Upon further incubation, an opaque zone is developed around colonies which can be due to lipolytic activity.
Baird-Parker Agar Base can also be used to detect coagulase activity by adding plasma fibrinogen mixture in place of egg yolk emulsion. 375 mg bovine fibrinogen, 2.5 ml rabbit plasma, 2.5 mg trypsin inhibitor and 2.5 mg potassium tellurite dissolved in 10 ml sterile distilled water and added to 90 ml sterile molten medium kept at 45-50°C (9). Mix well and pour into plates. On this medium Staphylococcal coagulase positive colonies are white to grey-black surrounded by an opaque zone of coagulase activity, within 24-40 hours incubation at 35°C. Reduction in tellurite is necessary because of absence of egg yolk emulsion. This results in translucent agar and white to grey coloured colonies of Staphylococci. For quantitative results, select 20 - 200 colonies. Count Staphylococcus aureus like colonies and test them for coagulase reaction. Report Staphylococcus aureus per gram of food. Regardless of the negative reactions, consider all doubtful colonies as Staphylococcus aureus and carry out further tests. Colonies of some contaminating organisms may digest the coagulase halo reaction.
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.
References:
1. Baird-Parker A.C., 1962, J. Appl. Bact., 25:12.
2. Baird-Parker A.C. and Davenport E., 1965, J. Appl. Bact., 28:390.
3. Zebovitz E., Evans J.B. and Niven C.F., 1955, J. Bact., 70:686.
4. Tardio and Baer, 1971, J. Assoc. Off. Anal. Chem., 54:728.
5. Baer, 1971, J. Assoc. Off. Anal. Chem., 54:732.
6. J. Assoc. off. Anal. chem, 1971, 54:401.
7. The United States Pharmacopoeia, 1995, 23rd rev., USP Convention, Rockville, Md.
8. Smith B.A. and Baird-Parker A.C., 1964, J. Appl. Bact., 27:78.
9. Beckers N. J. et al, 1984, Can. J. Microbiol., 30:470.
10. International Organization for Standardization (ISO), 1983, Draft ISO/DIS 6888
11. Bureau of Indian Standards IS : 5887 (Part II) 1976, (Second Reprint December 1994.