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Brilliance Staph 24 AGAR

Code: PO1186

Brilliance Staph 24 is a selective, chromogenic medium for the isolation and enumeration of coagulase-positive staphylococci in foods within 24 hours.

*Adjusted to meet performance standards

Description
Staphylococcus species are found in a broad range of commercial foods, including meat and meat products, poultry and egg products, salads, bakery products (such as cream-filled pastries), sandwich fillings, and milk and dairy products. Food products that require considerable handling during preparation or are kept at slightly elevated temperatures after preparation are frequently involved in staphylococcal food poisoning. Humans and animals remain the primary source of this organism ,and as it is part of the normal flora of healthy individuals, it can be easily transferred to food through bad hygiene and handling practices.

Most species of staphylococci can produce some form of enterotoxin, the causative agent of staphylococcal enteritis. The production of these enterotoxins strongly correlates with the production of coagulase and/or thermonuclease¹, both of which are used as markers of pathogenecity. When coagulase-positive staphylococci (CPS) are prevalent in low numbers, as they are in many foods, they pose a limited risk of infection. However, if food is stored incorrectly, CPS can proliferate to numbers in excess of 1x10⁵ cells/g. This level is considered sufficient to produce enough enterotoxin to induce gastroenteritis, characterized by nausea, vomiting, and stomach cramps. The infection is usually self-limiting, and patients usually recover in a few days. Consequently, food poisoning by CPS is thought to be considerably under-reported due to the short duration of the infection. The greatest number of infections occurs in the summer months, when improperly stored foods reach the highest temperatures. CPS infection can generally be avoided by employing standard hygiene principles for preparing and cooking food.

Brilliance Staph 24 Agar is a selective, chromogenic medium for the isolation and enumeration of coagulase-positive staphylococci in foods within 24 hours. Coagulase-positive staphylococci (CPS) grow as dark blue colonies on a clear background, making it much easier to read than existing Baird-Parker Agar formulations. A result is achieved in 24 hours, far quicker than the 48h required for Baird-Parker Egg Yolk Tellurite Agar (BP-EYT). Selective agents have been carefully designed to inhibit the growth of Gram-negative flora and nontarget Gram-positive organisms. Sodium pyruvate is added to improve the recovery of stressed cells, and a carefully formulated blend of peptones and growth factors ensures rapid growth of target organism. The chromogen is specifically activated by CPS which colours positive colonies dark blue, while coagulase-negative staphylococci are inhibited or remain colourless.

Technique

1. Prepare samples in accordance with ISO 6887², ISO 8261³ or the appropriate standard
2. Prepare required number of dilutions in a suitable diluent such as Buffered Peptone Water ISO (CM1049) or Maximum Recovery Diluent (CM0733)
3. In duplicate, spread 0.1ml aliquots of required dilutions over plates until absorbed
4. Incubate the inverted dishes at 37°C±1°C for 24h±2h and then count dark blue colonies
5. Select 5 dark blue colonies, inoculate into tubes of Brain Heart Infusion Broth (CM1135) and incubate at 37°C±1°C for 24h±2h
6. Add 0.5ml of each sample to 0.5ml of rabbit plasma and incubate at 37°C±1°C
7. Examine for clotting of the plasma every 30min to 4h of incubation. If negative reexamine after 24h
8. Report number of CPS per gram of food

For further instructions on the use and interpretation of Brilliance Staph 24 Agar, simply download data sheet in PDF format.

Validation
Brilliance Staph 24 Agar is validated in accordance with ISO 16140 by MicroVal against ISO 6888-1:1999 Horizontal method for the enumeration of coagulase-positive staphylococci Part 1: Technique using Baird-Parker agar medium⁴ for meat, dairy, seafood, bakery products and composite foods. A copy of the certificate can be obtained at www.microval.org.

Storage Conditions and Shelf life
Brilliance Staph 24 Agar plates should be stored in the original packaging at the temperature stated on the pack or product specification. When stored as directed, the unopened product will remain stable until the expiry date on the label.

Appearance
Prepared medium: transparent gel in Petri dishes

Quality control

Precautions
Brilliance Staph 24 Agar is for in vitro diagnostic use only, by experienced microbiologists. It must not be used beyond the stated expiry date, or if the product shows any sign of deterioration. Sterilise specimens, equipment, and media properly after use.

Limitations
During validation Brilliance Staph 24 Agar may give some underestimation of coagulase-positive staphylococci due to overgrowth with competing flora for some green vegetables such as sugar snap peas.

References
1. Victor R, Lachica F, Weiss KF, Deibel RH. (1969) Appl Microbiol 18. 126-7
2. ISO 6887-1:1999 Microbiology of food and animal feeding stuffs -- Preparation of test samples, initial suspension and decimal dilutions for microbiological examination
3. ISO 8261:2001 Milk and milk products -- General guidance for the preparation of test samples, initial suspensions and decimal dilutions for microbiological examination
4. 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