ASCP International (ASCPi) Practice Exam 2026 - Free ASCPi Practice Questions and Study Guide

CIN medium is formulated to selectively isolate Yersinia enterocolitica by using antibiotics that inhibit many other Gram-negative and Gram-positive bacteria. Yersinia typically forms distinctive “bull’s-eye” colonies on CIN due to mannitol fermentation, which gives a characteristic appearance. Among common enteric bacteria, Aeromonas species can also grow on CIN because they tolerate the selective agents present, so they may be recovered on this medium even though they are not Yersinia. The other organisms listed—Pseudomonas, Enterobacter, and Klebsiella—are generally inhibited by the CIN antibiotics and do not form the same characteristic growth on this medium.