Yersinia (CIN) Agar is a selective and differential culture medium formulated for the isolation and differentiation of Yersinia species, particularly Yersinia enterocolitica, from clinical, food, and environmental samples.

The formulation contains peptones and yeast extract to support bacterial growth, while the selective agents Cefsulodin, Irgasan, and Novobiocin (CIN) suppress much of the accompanying flora. Mannitol and neutral red provide differential colony development based on fermentation reactions.

On CIN Agar, typical Y. enterocolitica colonies appear as deep red “bull’s-eye” colonies with a translucent peripheral zone, enabling visual differentiation from many competing Enterobacteriaceae. This medium is widely used in food microbiology, public health laboratories, and research environments requiring reliable isolation of Yersinia.

CIN Agar relies on a selective antibiotic system combined with differential carbohydrate metabolism. Cefsulodin, Irgasan, and Novobiocin suppress much of the accompanying flora, improving recovery of Yersinia species. Mannitol fermentation by Y. enterocolitica results in localized acid production, which is visualized by the pH indicator neutral red as a deep red colony center. The typical “bull’s-eye” appearance results from intense localized fermentation surrounded by a translucent margin.