Cefsulodin-irgasan-novobiocin (CIN) agar is recommended for the recovery of which organism?

• A. Brucella suis
• B. Cardiobacterium hominis
• C. Rhodococcus equi
• D. Yersinia enterocolitica

Answer: (D)

CIN agar is a selective-differential medium designed to recover Yersinia enterocolitica from clinical specimens. The combination of cefsulodin, irgasan, and novobiocin suppresses many other bacteria, allowing Yersinia to grow. Differentially, the medium uses mannitol and a pH indicator so that Yersinia ferments mannitol, producing a distinctive “bull’s-eye” colony—red center with a pale halo—on the plate. This characteristic appearance is a key identifying feature for Yersinia enterocolitica in mixed flora, which is why CIN is specifically used for its recovery. The other organisms listed do not produce this bull’s-eye morphology on CIN and are typically recovered on different media or under different conditions.