Cefsulodin-irgasan-novobiocin (CIN) agar is primarily used 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 isolate Yersinia enterocolitica from clinical specimens. The combination of antibiotics (cefsulodin, irgasan, and novobiocin) inhibits many competing bacteria, so Yersinia can grow more readily. The medium also includes mannitol and a pH indicator; Y. enterocolitica ferments mannitol, producing acid that turns the center of the colony red, while the surrounding nonfermenting area remains pale. This gives the characteristic “bull’s-eye” colony appearance that makes Y. enterocolitica stand out on CIN.

The other organisms listed are not specifically recovered or distinguished on CIN as Yersinia is, so CIN’s key use is toward recovering Y. enterocolitica from stool or other specimens.