ASCP Technologist in Microbiology (M) Practice Exam – Prep Guide & Study Questions 2026

Yersinia enterocolitica, when cultured on CIN (Cefsulodin-Irgasan-Novobiocin) agar, typically produces clear colonies with a characteristic red pinpoint center. This distinctive appearance is due to the selective properties of the CIN medium, which is designed to isolate Yersinia species while inhibiting the growth of other bacteria. The clear appearance of the colonies corresponds to the mucin-degrading characteristics of Yersinia, and the red pinpoint center results from the fermentation of mannitol, which is present in the medium. This specific colony morphology serves as an important clue for microbiologists in identifying Yersinia enterocolitica amidst other flora present in a clinical or environmental sample.