Final answer:
The correct selective medium for Yersinia enterocolitica, Aeromonas, and Plesiomonas shigelloides is d) Cefsulodin-irgasan-novobiocin (CIN) agar, which is specifically designed to inhibit the growth of other organisms and support these species.
Step-by-step explanation:
The selective medium for Yersinia enterocolitica, Aeromonas, and Plesiomonas shigelloides is d) Cefsulodin-irgasan-novobiocin (CIN) agar, which is answer option d).
CIN agar is specifically formulated to support the growth of Yersinia species while inhibiting the growth of other organisms.
The medium includes cefsulodin and novobiocin antibiotics to suppress competing flora and irgasan to inhibit Gram-positive bacteria.
Selective media, like the MacConkey agar, are designed to suppress the growth of unwanted microorganisms while supporting the growth of the organism of interest.
MacConkey agar is not the correct answer since it's predominantly used for differentiating lactose fermenters among Gram-negative enterics.
In contrast, Hektoen enteric agar and Xylose-lysine-deoxycholate agar, options b) and c), are also used for the isolation of other enteric pathogens but are not as specific for Yersinia enterocolitica, Aeromonas, and Plesiomonas shigelloides as CIN agar is.