Baird-Parker Medium Base ISO

Description

The presence of tellurite and egg yolk, which must be added to the medium after sterilization, allows the differentiation of presumptive pathogenic staphylococcal colonies. There is a high correlation between the coagulase test and the presence of clear zones of lipolysis in this medium, which is due to the staphylococcal lecithinase. Studies show that almost 100% of coagulase-positive staphylococci are capable of reducing tellurite, which produces black colonies, whereas other staphylococci cannot always do so.

Technique

To use, the contents of the bottle should be poured into plates. The melting of the culture medium should be carried out according to the manufacturer's instructions, either in a water bath or microwave oven. Never apply direct heat to melt a medium. The melting temperatures and times depend on the shape of the container, the volume of medium and the heat source. Before melting any medium, loosen the screw cap of the container to avoid breaking the container. The medium should be melted only once and used. Media with agar should not be melted repeatedly as their characteristics change with each remelting. Overheating should be avoided as much as prolonged heating, especially with regard to media with an acidic or alkaline pH. Once melted, pour the plates using aseptic techniques.

Prepare the complete medium by adding 50 mL/L medium of sterile egg yolk + potassium tellurite emulsion. Homogenize and distribute into plates.

To inoculate, follow standard laboratory methods or the applicable norms: spiral plate method, streak plating, ecometric methods, dilution banks or spread plating.

The use methodology is according to ISO 6888.

After 24-48 hours of incubation at 37 ± 1 °C, select the colonies which are black, shiny and convex with regular margins surrounded by a clear zone (lecithinase +). These can be presumptively identified as coagulase-positive Staphylococcus aureus. To confirm the coagulase test, inoculate the colony in the medium RPF Baird Parker Agar.

LC-4678, 250 mL bottles

Prepare the complete medium by adding 50 mL/L medium of sterile egg yolk + potassium tellurite emulsion. Plates should be used on the same day of preparation or within 48 hours, to avoid the loss of definition in the precipitated zones. The medium base, without yolk or tellurite, is perfectly stable and therefore can be melted repeatedly.

The use methodology is according to EN ISO 6888.

The inoculation is carried out by spreading 0.5 mL of sample over each plate with a Drigalski loop. After 24-48 hours of incubation at 37 ± 1 °C, select the colonies which are black, shiny and convex with regular margins surrounded by a clear zone. These can be presumptively identified as coagulase-positive Staphylococcus aureus.

Physical/chemical control

Microbiological control

Add egg yolk tellurite - inoculate: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ (selectivity).

Distribute the complete medium, cooled at 50 °C, in plates.

Aerobiosis. Incubation at 37 ± 1 °C, reading after 24/44 ± 4 h.

LC-4678, 250 mL bottles: microbiological control

Add supplement for functionality testing - inoculate: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ (selectivity).

Distribute the complete medium, cooled at 50 °C, in plates.

Aerobiosis. Incubation at 37 ± 1 °C, reading after 24/44 ± 4 h.

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.