CAS agar assay.

The ability of A. baumannii ATCC 19606^T and isogenic iron uptake mutants to produce iron chelators (siderophores) was investigated using the CAS agar assay (24). Briefly, 1 ml of bacterial culture grown at 37°C in LB was washed with sterile saline and diluted to obtain ca. 10⁸ cells/ml. Ten microliters of this bacterial suspension was spotted on CAS agar plates and incubated for up to 48 h at 37°C. The halo around each spot provided a semiquantitative estimation of the amount of released siderophores.