RPF Supplement ISO

The ISO 6888-2 Standard recommends the addition of Rabbit Plasma Fibrinogen (RPF) Supplement to Baird-Parker Agar Base (LC-1100), to make Rabbit Plasma Fibrinogen (RPF) Agar used for food (such as cheese made from raw milk and certain raw meat products) that may be contaminated with staphylococci forming non-characteristic colonies in Baird Parker Agar or with base flora that can mask the colonies sought. This medium should be used immediately after preparation.

In Rabbit Plasma Fibrinogen Agar, staphylococcus colonies are small, black or gray, even white, surrounded by a halo of precipitation indicating the coagulase activity. At the start of incubation, Proteus colonies can present similar physical characteristics to coagulase-positive Staphylococcus aureus colonies. However, after 24 or 48 hours of incubation, they can acquire a brown color that expands and invades the plate, and which allows them to be distinguished from staphylococcus.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Reconstitute one vial of the RPF Supplement ISO with 10 mL of sterile distilled water (preheated to 37 °C) and add aseptically to 90 mL of Baird Parker Agar Base (LC-1100) autoclaved and cooled to 45-50 °C. Homogenize gently and dispense into Petri dishes.

Instructions for use

Enumeration of coagulase-positive staphylococci by the technique using Rabbit Plasma Fibrinogen Agar:

• Inoculate 1 mL of the liquid sample or 1 mL of the initial suspension by the pour plate method. Inoculate also the first decimal dilution.
• Incubate the plates at a temperature of 35-37 °C for 18-24 hours. If needed, reincubate for a further 18-24 hours at the same temperature.
• Count the characteristic colonies.

• Baird Parker, A.C. (1962). An improved diagnostic and selective medium for isolating coagulase-positive staphylococci. J. Appl. Bact. 25 (1): 12-19.
• Beckers N.J. et al (1984). Canad J. microbiol. 30: 470-474.
• ISO 6888-2. Enumeration of Staphylococcus aureus using RPF medium.
• ISO 6888-1. 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.