The appropriate culture medium for group D Streptococcus is:

Bile Esculin Agar is specifically designed to isolate and identify group D Streptococcus, particularly Streptococcus faecalis. This medium contains bile salts, which inhibit the growth of most gram-positive organisms while allowing enterococci and group D streptococci to thrive. Additionally, the agar contains esculin, which these bacteria can hydrolyze, leading to the formation of a dark brown complex due to the reaction with iron salts present in the medium. This distinctive color change is an indicator of the presence of group D Streptococcus.

In contrast, the other culture media listed serve different purposes. Mannitol salt agar is selective for staphylococci, particularly Staphylococcus aureus, and is not suitable for culturing Streptococcus species. Chocolate agar is a non-selective medium used primarily for growing fastidious organisms, such as Haemophilus species and Neisseria, rather than for group D Streptococcus. MacConkey agar is selective for gram-negative bacteria, specifically enteric bacteria, and it does not support the growth of gram-positive bacteria like Streptococcus. Thus, Bile Esculin Agar is the correct choice for effectively isolating and identifying group D Streptococcus.