Part of Thermo Fisher Scientific

Thermo Scentific
 
 
 

Material Safety Data Sheet

Required Products

Organisms

Organisms this product works with:

Dehydrated Culture Media

BAIRD-PARKER AGAR BASE (RPF)

Code: CM0961

a new improved base medium for use with RPF Supplement (SR0122). This conforms to ISO 6888 Part 21 for the enumeration of coagulase-positive staphylococci.

Typical Formula*

gm/litre

Pancreatic digest of casein

10.0

Meat extract

5.0

Sodium pyruvate

10.0

Yeast extract

1.0

Glycine

12.0

Lithium chloride

5.0

Agar

20.0

pH 7.2 ± 0.2 @ 25ºC

 
* Adjusted as required to meet performance standards

RPF SUPPLEMENT

Code: SR0122

Typical Formula

SR0122A
(1 vial per 100ml
medium)

per litre

Bovine fibrinogen

375mg

3.75g

Rabbit plasma

2.5ml

25.0ml

Trypsin inhibitor

2.5mg

25.0mg

Potassium tellurite

2.5mg

25.0mg

Directions
Suspend 6.3g of Baird-Parker Agar Base (RPF) in 90ml of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121ºC for 15 minutes. Cool to 48ºC and add 1 vial of SR0122A, reconstituted as directed. Mix well and pour plates.

N.B.: Baird-Parker Agar Base (RPF) should only be used with RPF Supplement SR0122

Description
Staphylococcus aureus is a Gram-positive coccus capable of producing enterotoxin which can induce food poisoning. The organisms may be present in small numbers in many foods, and, if allowed to multiply unchecked, may produce highly heat resistant enterotoxins. The ability of Staphylococcus aureus to produce lecithinase and lipase has been recognised for many years, and the detection of these enzymes in egg yolk media has become a widely used procedure for the identification of this organism. Its ability to produce coagulase using a similar basal formulation enables confirmatory diagnosis with the incorporation of rabbit plasma into the base medium.

Rabbit Plasma Fibrinogen (RPF) Agar is based on the formulation described by Beckers et al2. This medium is a modification of Baird-Parker Medium and is recommended for the selective isolation, enumeration and confirmation of Staphylococcus aureus from food and other specimens3. The RPF Agar formulation retains the Baird-Parker Agar Base which has been specifically formulated to resuscitate injured cells4. This medium differs from Baird-Parker Medium in that the egg yolk emulsion has been replaced by fibrinogen, rabbit plasma and trypsin inhibitor. The fibrinogen was added to enhance the coagulase reaction in the RPF Agar5. The addition of rabbit plasma was found to be more specific for the coagulase activity when compared to other sources of plasma2. Trypsin inhibitor was added to prevent fibrinolysis.

The RPF Supplement (SR0122) has been modified in one respect from the original formulation, in that the potassium tellurite content has been reduced four-fold, from 0.01% to 0.0025% w/v. This reduction was necessary as it was discovered in the Oxoid laboratory that some strains of Staphylococcus aureus were sensitive to potassium tellurite when used at 0.01% w/v in RPF Agar6. This modification of RPF Agar was found to give comparable growth and selectivity to that achieved on Baird-Parker Medium (CM0275 or CM1127 and SR0054). The improved productivity of RPF Agar has also been confirmed by other laboratories7,8. The reduction in potassium tellurite concentration in RPF Agar results in Staphylococcus aureus strains forming white, grey or black colonies, which are surrounded by an opaque halo of precipitation, i.e. the coagulase reaction.

Technique
Surface Inoculation Method

  1. Prepare the RPF Agar plates as directed.
  2. Process the food sample in a stomacher or Waring blender using the recommended sample size and diluent.
  3. Separate plates are inoculated with 0.1ml of the prepared samples and the subsequent decimal dilutions of them.
  4. Incubate at 35°C or 37°C and examine after 24 and 48 hours incubation.
  5. Count all the colonies that have an opaque halo of precipitation around them. Do not limit the count to black colonies.
  6. Report as number of coagulase positive staphylococcus isolated per gram of food.

Pour Plate Method

  1. Prepare the RPF Agar as directed and hold at 48°C.
  2. Process the food sample in a stomacher or Waring blender using the recommended sample size and diluent.
  3. Add 1ml of the prepared sample (initial suspension and subsequent decimal dilution) into each sterile Petri dish.
  4. Add aseptically 20ml of sterile RPF Agar and prepare pour plates.
  5. Incubate at 35°C or 37°C and examine after 24 to 48 hours.
  6. Count all the colonies that have an opaque halo of precipitation around them.
  7. Report as number of coagulase positive staphylococcus isolated per gram of food.

Storage Conditions and Shelf Life
Store the dehydrated medium at 10-30°C and RPF Supplement below 0°C. Use before the expiry date on the label.
Prepared plates of medium are best used freshly prepared1,2.

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured gel

Quality Control

Quality control of the medium includes testing in accordance with ISO 111339.

Positive control:

Expected results

Staphylococcus aureus ATCC® 25923*
WDCM00034

1-3 mm grey/black colonies coagulase zones

Negative control:

 
Staphylococcus saprophyticus ATCC® 15305*
WDCM00159
No growth pinpoint - 2 mm grey/black colonies, no zone
Escherichia coli ATCC® 25922*
WDCM00013
No growth
* This organism is available as a Culti-Loop®

Precautions
Colonies of some contaminating organisms growing in close proximity to the coagulase positive colonies may partially digest the coagulase halo reaction.

References

1. International Organization for Standardization ISO 6888-2 (1999) Microbiology of food and animal feeding stuffs - Enumeration of coagulase positive staphylococci (Staphylococcus aureus and other species) – Part 2 Technique using rabbit plasma fibrinogen agar.
2. Beckers H. J., van Leusden F. M., Hogeboom W. M. and Delfgon-van Asch E. H. M. (1980) (English summary) De Ware(n)-Chemicals 10. 125-130.
3. Beckers H. J., van Leusden F. M., Bindshedler O. and Guerraz D. (1984) Can. J. Microbiol. 30. 470-474.
4. Baird-Parker A. C. (1962) J. Appl. Bacteriol. 25. 12-19.
5. Hauschild A. H. W., Park C. E. and Hilsheimer R. (1979) Can. J. Microbiol. 25. 1052-1057.
6. Sawhney D. (1986) J. Appl. Bact. 61. 149-155.
7. Beckers H. J. (1985) Personal Communication.
8. van Schothorst M. (1985) Personal Communication.
9. International Organization for Standardization ISO 11133:2014 Microbiology of food, animal feed and water - Preparation, production, storage and performance testing of culture media

 
©2001 - 2021 Oxoid Limited, All rights reserved.
Copyright, Disclaimer and Privacy Policy | Conditions of Sale | About Us | Cookies
Thermo Fisher Scientific Inc.