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BAIRD-PARKER AGAR (ISO) BASE

Code: CM1127

Baird-Parker Agar (ISO) is a selective and diagnostic medium for the isolation and enumeration of coagulase-positive staphylococci in foods. When used with egg yolk tellurite this medium meets the formulation and performance criteria described in ISO 6888 parts 1 and 31,2  and ISO 11133:20143.

Typical Formula* gm / litre
Pancreatic digest of casein 10.0
Meat extract 5.0
Yeast extract 1.0
Sodium pyruvate 10.0
L-glycine 12.0
Lithium chloride 5.0
Agar 20.0
pH 7.2 ± 0.2 @ 25°C  
*Adjusted as required to meet performance standards
† pH of supplemented medium

Directions
Suspend 63g of Baird-Parker Agar (ISO) Base in 1,000ml of distilled water.  Boil to dissolve the medium and sterilise by autoclaving at 121°C for 15 minutes. Cool to 47°C and aseptically add 50ml of Egg Yolk Tellurite Emulsion (SR0054). Mix well and pour into sterile Petri dishes.

Description (supplemented medium)
Baird-Parker4 developed this agar medium from the tellurite-glycine formulation of Zebovitz et al.5 and improved its reliability in isolating coagulase-positive staphylococci from foods. Baird-Parker added egg yolk emulsion as a diagnostic agent and sodium pyruvate to protect damaged cells and aid their recovery6. It is now widely recommended by national and international bodies for the isolation of coagulase-positive staphylococci7 and is included in Microbiology of food and animal feeding stuffs-Horizontal method for the enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species) ISO 6888-1:1 and ISO 6888-3: Detection and MPN technique for low numbers2.

The selective agents; glycine, lithium and tellurite have been carefully balanced to suppress the growth of most bacteria present in foods, without inhibiting coagulase-positive staphylococci. Egg yolk emulsion makes the medium cream/yellow and opaque. Coagulase-positive staphylococci reduce tellurite to form black/grey shiny colonies which, after 48 hours, produce clear zones around the colonies caused by the proteolysis of egg yolk. This clear zone with typical black/grey colony is diagnostic for coagulase-positive staphylococci. On further incubation, most strains of coagulase-positive staphylococci form opaque haloes around the colonies; this is thought to be due to the action of a lipase. Not all strains of coagulase-positive staphylococci produce both reactions.

Some strains of coagulase-negative Staphylococcus saprophyticus produce both clear zones and opaque haloes but experienced workers can distinguish these from other organisms by the longer incubation time required8. Certain foods, especially cheese, may produce typical black/grey colonies of coagulase-positive staphylococci but without the typical egg yolk reaction. These can be confirmed by performing a tube coagulase test9.

Baird-Parker and Davenport10 showed that the recovery of damaged staphylococci was greater on Baird-Parker Agar than on other recovery media tested. Broeke11 and de Waart et al.12 found Baird-Parker Agar valuable in ecological studies on foods incriminated in staphyloenterotoxicosis. Of the 522 strains of Staphylococcus aureus tested, isolated from human and food origins, 97.5% developed characteristic colonies on Baird-Parker Agar.

Technique
Refer to the relevant standard method for detailed instructions. The following method is a summary of ISO 6888-1:19991:

  1. Prepare samples in accordance with ISO 688713, or the appropriate standard
  2. Spread 0.1ml aliquots of food dilutions made up in a suitable diluent such as Buffered Peptone Water (CM1049) over the plate until absorbed. Up to 1.0ml may be used on larger dishes
  3. Incubate the inverted dishes at 35°C or 37°C. Examine after 24h ± 2h and look for typical colonies of coagulase-positive staphylococci
  4. Re-incubate negative plates for a further 24h ± 2h
  5. For quantitative results, count presumptive coagulase-positive staphylococci colonies and confirm by tube coagulase (R21052, R21060), Staphylase (DR0595), or Staphytect Plus (DR0850)
  6. Report coagulase-positive staphylococci 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.
The prepared medium is best used freshly prepared, but may be suitable for longer storage following in-house validation.

Appearance
Dehydrated culture medium: Straw coloured, free-flowing powder
Prepared medium: Cream/yellow, opaque gel

Quality Control

Positive controls: Expected results (at 48 hours)
Staphylococcus aureus ATCC® 25923*
WDCMooo34
Good growth; black, shiny colonies with white and clear zones
Staphylococcus aureus ATCC® 6538*
WDCM00032
Good growth; black, shiny colonies with white and clear zones
Negative controls  
Staphylococcus epidermidis ATCC® 12228* WDCM00036 No growth or ppt-1mm black colonies, no zones
Staphylococcus saprophyticus ATCC® 15305*
WDCM00159
0.5 - 2 mm black colonies, no zones
Eschericheria coli ATCC® 25922*
WDCM00013
No growth
Eschericheria coli ATCC® 8739*
WDCM00013
No growth
*available as Culti-loop®

Precautions
Atypical colonies have the same size as typical colonies but can be shining black with or without a narrow white edge; the clear zone or opacity halo can also be absent or barely visible. Grey colonies, free of clear zone, can also be regarded as atypical.
Regard all typical and atypical colonies as coagulase-positive staphylococci irrespective of negative reactions on 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.

Refs
1. ISO 6888-1:1999 Microbiology of food and animal feeding stuffs -- Horizontal method for the enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species) - Part 1: Technique using Baird-Parker agar medium
2. ISO 6888-3:2003 Microbiology of food and animal feeding stuffs -- Horizontal method for the enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species) - Part 3: Detection and MPN technique for low numbers
3 ISO 11133:2014 ISO 11133:2014. Microbiology of food, animal feed and water - Preparation, production, storage and performance testing of culture media.
4. Baird-Parker A. C. (1962) J. Appl. Bact. 25. 12-19.
5. Zebovitz E., Evans J. B. and Niven C. F. (1955) J. Bact. 70. 686-689.
6. Baird-Parker A. C. (1963) J. Gen. Microbiol. 30. 409-413.
7. 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.
8. Shaw S., Scott M. and Cowan T. (1957) J. Gen. Microbiol. 5. 1010-1023.
9. Devries L. A. and Hajek V. (1960) J. Appl. Bact. 49. 1-11.
10. Baird-Parker A. C. and Davenport E. (1965) J. Appl.Bact. 28. 390-402.
11. Broeke R. Ten (1967) Antonie van Leeuwenhoek 33. 220-236.
12. Waart J., de Mossel D. A. A., Broeke R. Ten and Moosdijk A. van de (1968) J. Appl. Bact. 31. 276-285.
13. ISO 6887 series Microbiology of the food chain - Preparation of test samples, initial suspension and decimal dilutions for microbiological examination

 
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