Final answer:
EMB agar is both a selective and differential medium, inhibiting the growth of gram-positive bacteria and distinguishing between lactose fermenters and non-lactose fermenters by colony color changes.
Step-by-step explanation:
EMB agar is a type of microbiological medium used for isolating and differentiating between different types of bacteria, particularly those found in fecal matter. It contains digested meat proteins that provide organic nutrients, and two indicator dyes, eosin and methylene blue.
These dyes are inhibitory to the growth of many gram-positive bacteria. Regarding the categories of media, EMB agar serves two main functions: It is a selective medium because it inhibits the growth of gram-positive microorganisms, thus selecting for gram-negative bacteria, like those in the Enterobacteriaceae family.
Additionally, it's a differential medium based on the ability of organisms to ferment lactose, which results in a color change of the colonies or medium. Lactose fermenters form metallic green or deep purple colonies on EMB agar, while non-lactose fermenters produce colorless colonies.
Therefore, the correct answer to the question about what category of media EMB agar belongs to is D) a selective medium, a differential medium, and a complex medium.