Which gram-negative rod is most likely identified in a case with "bulls-eye" colonies on CIN agar?

Which gram-negative rod is most likely identified in a case with "bulls-eye" colonies on CIN agar?

• A. E. coli
• B. Proteus mirabilis
• C. Yersinia enterocolitica
• D. Klebsiella pneumoniae

Answer: (C)

CIN agar, or Cefsulodin-Irgasan-Novobiocin agar, is a selective medium used specifically to isolate Yersinia enterocolitica, among other organisms. The characteristic "bulls-eye" colonies observed on this medium are particularly indicative of Yersinia enterocolitica due to the unique pigmentation and morphology that this organism exhibits when grown on CIN agar. Yersinia enterocolitica is a significant pathogen associated with gastroenteritis and is often transmitted through contaminated food and water. The "bulls-eye" appearance of the colonies is a result of the organism's ability to ferment mannitol, which leads to a color change on the agar. This distinctive colony morphology is a key diagnostic feature that helps microbiologists identify the presence of Yersinia enterocolitica in clinical specimens. In contrast, while other Gram-negative rods such as E. coli, Proteus mirabilis, and Klebsiella pneumoniae may grow on various types of agar, they do not produce the characteristic "bulls-eye" colonies on CIN agar and therefore are unlikely to be the focus of identification in this context.

CIN agar, or Cefsulodin-Irgasan-Novobiocin agar, is a selective medium used specifically to isolate Yersinia enterocolitica, among other organisms. The characteristic "bulls-eye" colonies observed on this medium are particularly indicative of Yersinia enterocolitica due to the unique pigmentation and morphology that this organism exhibits when grown on CIN agar.

Yersinia enterocolitica is a significant pathogen associated with gastroenteritis and is often transmitted through contaminated food and water. The "bulls-eye" appearance of the colonies is a result of the organism's ability to ferment mannitol, which leads to a color change on the agar. This distinctive colony morphology is a key diagnostic feature that helps microbiologists identify the presence of Yersinia enterocolitica in clinical specimens.

In contrast, while other Gram-negative rods such as E. coli, Proteus mirabilis, and Klebsiella pneumoniae may grow on various types of agar, they do not produce the characteristic "bulls-eye" colonies on CIN agar and therefore are unlikely to be the focus of identification in this context.