Abstract
The availability of highly productive and selective media for the detection and enumeration of Staphylococcus aureus is of great importance in routine food surveillance programmes. In this chapter recent developments in selective and diagnostic media, especially for stressed S. aureus cells and for food samples with high amounts of accompanying flora, are reviewed and an overview of media recommended by international and national standard organisations is given. Baird-Parker agar is widely accepted as the most satisfactory medium for the enumeration of coagulase-positive staphylococci in foods. Productivity is high especially in the case of stressed cells. However, tellurite reduction and egg yolk reaction are poor diagnostic systems for many foodstuffs and the medium is not completely selective. This may cause unreliable results in cases of samples with high levels of concomitant flora. Attempts have therefore been made to replace the egg yolk by animal plasma in order to differentiate coagulase-positive staphylococci from other competing micro-organisms directly on the plate. Results show that commercially available rabbit plasma fibrinogen agar is a suitable medium for enumerating coagulase-positive staphylococci in foods without the need for cumbersome and time-consuming confirmatory tests. Baird-Parker agar and rabbit plasma fibrinogen medium are recommended by the International Organisation for Standardisation (ISO). Baird-Parker agar is used also in the official AOAC method in the United States. Selective liquid media that use MPN techniques are available for detecting low numbers of coagulase-positive staphylococci (
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call