Part of Thermo Fisher Scientific
Organisms this product works with:
BAIRD-PARKER AGAR BASE
Code: CM0275
a selective and diagnostic medium for the isolation and enumeration of Staphylococcus aureus in foods
Typical Formula* |
gm/litre |
Tryptone |
10.0 |
`Lab-Lemco’ powder |
5.0 |
Yeast extract |
1.0 |
Sodium pyruvate |
10.0 |
Glycine |
12.0 |
Lithium chloride |
5.0 |
Agar |
20.0 |
pH 6.8 ± 0.2 @ 25°C |
Directions
Suspend 63g in one litre of distilled water and boil to dissolve the medium and sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C and aseptically add 50ml of Egg Yolk Tellurite Emulsion (SR0054). Alternatively, 50ml of Egg Yolk Emulsion (SR0047) and 3ml of Potassium Tellurite 3.5% (SR0030) can be used. Mix well before pouring into sterile Petri Dishes.
Description
Baird-Parker1 developed this medium from the tellurite-glycine formulation of Zebovitz et al.2 and improved its reliability in isolating Staphylococcus aureus from foods. Baird-Parker added sodium pyruvate, to protect damaged cells and aid their recovery2 and egg yolk emulsion as a diagnostic agent. It is now widely recommended by national and international bodies for the isolation of Staphylococcus aureus 4.
The selective agents glycine, lithium and tellurite have been carefully balanced to suppress the growth of most bacteria present in foods, without inhibiting Staphylococcus aureus.
Egg yolk emulsion makes the medium yellow and opaque. Staphylococcus aureus reduces tellurite to form grey-black shiny colonies and then produces clear zones around the colonies by proteolytic action. This clear zone with typical grey-black colony is diagnostic for Staphylococcus aureus (see Table 1 for typical reactions). On further incubation, most strains of Staphylococcus aureus form opaque haloes around the colonies. This is probably due to the action of a lipase. Not all strains of Staphylococcus aureus produce both reactions. Some strains of Staphylococcus saprophyticus produce both clear zones and opaque haloes but experienced workers can distinguish these from Staphylococcus aureus by the longer incubation time required5.
Colonies typical of Staphylococcus aureus but without an egg yolk reaction should also be tested for coagulase production6. Egg yolk reaction negative strains of Staphylococcus aureus may occur in some foods, especially cheese. Smith and Baird-Parker7 found that the addition of 50µg of sulphametazine per ml of medium suppressed the growth and swarming of Proteus species. Small numbers of Staphylococcus aureus could then be recovered from specimens containing mixed Proteus strains.
Baird-Parker and Davenport8 showed that the recovery of damaged staphylococci was greater on Baird-Parker medium than on other recovery media tested. Broeke9 and de Waart et al.10 found Baird-Parker medium valuable in ecological studies on foods incriminated in staphyloenterotoxicosis. Of the 522 strains of Staphylococcus aureus tested, 97.5% isolated from human and food origins developed characteristically and quantitatively on Baird-Parker medium.
Table 1: Colony characteristics of typical organisms on Baird-Parker Egg Yolk Tellurite Medium
Organism |
Growth |
Colony
|
Staphylococcus aureus |
Good |
Grey-black shiny convex 1-1.5 mm diameter (18 hours) up to 3 mm (48 hours) narrow white entire margin surrounded by zone of clearing 2-5mm
|
Staphylococcus epidermidis |
Variable |
Not shiny black and seldom produces clearing
|
Staphylococcus saprophyticus |
Variable |
Irregular and may produce clearing. Wide opaque zones may be produced in 24hrs
|
Micrococcus species |
Variable |
Very small in shades of brown and black. No clearing
|
Bacillus species |
Variable |
Dark brown matt with occasional clearing after 48hrs
|
Escherichia coli |
Variable |
Large brown-black
|
Proteus species |
Variable |
Brown-black with no clearing
|
Yeasts |
Variable |
White, no clearing
|
Technique
Quantitative results
Count the Staphylococcus aureus like colonies and test them for coagulase reaction.
Report Staphylococcus aureus results per gram of food.
Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Prepared plates of medium are best used freshly prepared11.
Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured gel
Quality control
Includes testing in accordance with ISO 11133:201412.
Positive controls: |
Expected results (48 hours) |
Staphylococcus aureus ATCC® 25923 * WDCM 00034 |
Good growth; black, shiny colonies with white and clear zones |
Staphylococcus aureus ATCC® 6538 * WDCM 00032 |
Good growth; black, shiny colonies with white and clear zones |
Negative controls: |
|
Staphylococcus epidermidis ATCC® 1222 * WDCM 00036 |
No growth or ppt-1mm black colonies, no zones |
Staphylococcus saprophyticus ATCC® 15305 * WDCM 00159 |
0.5 - 2 mm black colonies, no zones |
Escherichia coli ATCC® 25922 * |
No growth |
Escherichia coli ATCC® 8739 * |
No growth |
Precautions
Regard all suspicious colonies as Staphylococcus aureus regardless of negative reactions in the medium and carry out further tests.
Colonies of some contaminating organisms growing in close proximity to the coagulase positive colonies may partially digest the coagulase halo reaction.
References
1. Baird-Parker A. C. (1962) J. Appl. Bact. 25. 12-19.
2. Zebovitz E., Evans J. B. and Niven C. F. (1955) J. Bact. 70. 686-689.
3. Baird-Parker A. C. (1963) J. Gen. Microbiol. 30. 409-413.
4. Chopin A., Malcolm S., Jarvis G., Asperger H., Beckers H. J., Bertona A. M., Cominazzini C., Carini S., Lodi R., Hahn G., Heeschen W., Jans J. A., Jervis D., I., Lanier J. M., O’Connor F., Rea M., Rossi J., Seligmann R., Tesone S., Waes G., Mocquot G. and Pivnick H. (1985) ICMSF Methods studies XV. J. Food Protect. 48. 21-27.
5. Shaw S., Scott M. and Cowan T. (1957) J. Gen. Microbiol. 5. 1010-1023.
6. Devries L. A. and Hajek V. (1960) J. Appl. Bact. 49. 1-11.
7. Smith B. A. and Baird-Parker A. C. (1964) J. Appl.Bact. 27. 78-82.
8. Baird-Parker A. C. and Davenport E. (1965) J. Appl.Bact. 28. 390-402.
9. Broeke R. Ten (1967) Antonie van Leeuwenhoek 33. 220-236.
10. Waart J., de Mossel D. A. A., Broeke R. Ten and Moosdijk A. van de (1968) J. Appl. Bact. 31. 276-285.
11. Holbrook R., Anderson J. M. and Baird-Parker A. C. (1969) J. Appl. Bact. 32. 187-191.
12. ISO 11133:2014 Microbiology of food, animal feed and water - Preparation, production, storage and performance testing of culture media