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Material Safety Data Sheet

Organisms

Organisms this product works with:

Dehydrated Culture Media

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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

 
* Adjusted as required to meet performance standards

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

  1. Dry the surface of agar plates for a minimal period of time prior to use.
  2. With a glass spatula, spread 0.1ml aliquots of food dilutions made up in Buffered Peptone Water on the agar surface until it is dry. Up to 0.5ml may be used on larger dishes.
  3. Incubate the inverted dishes at 35°C. Examine after 24 hours and look for typical colonies of Staphylococcus aureus. Re-incubate negative cultures for a further 24 hours.

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 *
WDCM 00013

No growth

Escherichia coli ATCC® 8739 *
WDCM 00013

No growth
This organism is available as a Culti-Loop®

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

 
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