This is a selective medium for the isolation and enumeration of Yersinia spp. in clinical and food samples. It is made selective by the inclusion of Sodium desoxycholate, Crystal violet and the antimicrobials Cefsulodin, Novobiocin and Irgasan. Mannitol is also included which Yersinia ferments giving a colony that produces a ‘Bull’s Eye’ appearance. The majority of other enteric organisms are inhibited but if they do grow they produce a large pinkish colony with an opaque halo.