Validation of RAPID'Staph for enumeration of Staphylococcus aureus in foods. Performance-Tested Method.

RAPID'Staph (Bio-Rad Laboratories, Hercules, CA) is a medium for differentiation and enumeration of coagulase-positive Staphylococcus aureus in food. RAPID'Staph medium is based on a Baird Parker formula optimized for the detection and enumeration of S. aureus in 24 h. The principle of the medium relies on the capacity of S. aureus to reduce tellurite (production of black colonies) and to provoke proteolysis of egg yolk (production of clear halo around the colony). Four foods (pasteurized whole milk, custard pie, processed ham, and smoked salmon) were selected to compare the performance of RAPID'Staph agar to AOAC Official Method 975.55. Method comparison studies demonstrated excellent agreement between the methods. Inclusivity and exclusivity rates of the medium were 100%. RAPID'Staph agar performed as expected when minor procedural variations were introduced, validating the ruggedness of the method. There was no difference in performance between the dehydrated and ready-to-use formulations of the media.