Baird Parker RPF Base Agar ISO

Collect, dilute and prepare samples and volumes as required according to specifications, directives, official standard regulations and/or expected results.

Melt the medium contained in the bottles in a water bath (100 °C) or in a microwave oven, avoiding overheating, before pouring into Petri dishes when cooled to 40-45 °C, after having added a sterile reconstituted RPF supplement vial (1 vial / 90 mL medium base). Do not use this base with Egg Yolk Tellurite supplement.

Once solidified on a flat surface, spread the plates by streaking methodology or by spiral method.

Incubate the plates right side up aerobically at 37 ± 1 °C for 24-48 h.

After incubation, enumerate all the colonies that have appeared on the surface of the agar. S. aureus forms brilliant black colonies (tellurite reduction) always surrounded by a halo of fibrin.

Each laboratory must evaluate the results according to their specifications. Presumptive isolation of S. aureus must be confirmed by further microbiological and biochemical tests.

Calculate total microbial count per mL of sample by multiplying the average number of colonies per plate by the inverse dilution factor if a diluted sample was streaked. Report results as colony forming units (CFU) per mL or g along with incubation time and temperature.

Physical/chemical control

Microbiological control

Before addition of 1 reconstituted vial of RPF supplement.

Inoculate: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ (selectivity).

Aerobiosis. Incubation at 37 ± 1 °C, reading after 24-48 ± 2 h.

Microbiological control according to ISO 11133:2014.

Sterility control

Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.

Check at 7 days after incubation in same conditions.

• ATLAS R.M. & L.C. PARKS (1993) Handbook of Microbiological Media. CRC Press. London.
• BAIRD-PARKER, A.C. (1962) An improved diagnostic and selective medium for isolating coagulase-positive staphylococci. J. Appl. Bact. 25:12.
• COLIPA (1997) Guidelines on Microbial Quality Management (MQM). Brussels.
• DOWNES, F.P. & K. ITO (2001) Compendium of Methods for the Microbiological Examination of Foods. 4th ed. APHA. Washington. USA.
• EUROPEAN PHARMACOPOEIA (2007) 5th ed. Suppl. 5.6 § 2.6.13 Microbiological examination of non-sterile products. EDQM. Council of Europe. Strasbourg.
• FIL-IDF 60:2001 Standard. Lait et produits à base de lait - Detection des staphylocoques à coagulase positive - Technique du nombre le plus probable. Brussels.
• ISO 5944:2001 Standard. Milk and Milk based products - Detection of coagulase positive staphylococci - MPN Technique. Geneva.
• ISO 6888-1:1999/Amd 2:2018. Standard. 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. Amendment 2: Inclusion of an alternative confirmation test using RPFA stab method.
• ISO 6888-2:1999 Standard. Microbiology of food and animal feeding stuffs - Horizontal method for the enumeration of coagulase-positive staphylococci - Part 1 Technique using rabbit plasma fibrinogen agar medium. Geneva.
• ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.
• ISO 22718 Standard (2015). Cosmetics - Microbiology - Detection of Staphylococcus aureus.
• USP 31 - NF 26 (2008) <61> Microbial Limit Tests. US Pharmacopeial Conv. Inc. Rockville. MD. USA.
• ZANGERL, P. & H. ASPERGER (2003) Media used in the detection and enumeration of Staphylococcus aureus. In Handbook.