Use of Blue Agar CAS Assay for Siderophore Detection

Schwyn and Neiland developed a universal siderophore assay using chrome azurol S(CAS) and hexadecyltrimethylammonium bromide (HDTMA) as indicators. In Schwyn and Neiland’s original paper, the procedure given for making CAS agar is written in general terms and can be difficult to follow, especially for an individual who has limited experience making more complex media. Here, we give a step-by-step protocol for making the CAS agar plates, and we discuss how this media can be incorporated in a comprehensive project in a microbiology lab course for biology majors.