Eosin-methylene blue agar is best described as?

Eosin-methylene blue (EMB) agar is best described as selective and differential media, which is why this choice is accurate. The medium is designed to selectively inhibit the growth of gram-positive bacteria while allowing gram-negative bacteria to grow. This selectivity is due to the dyes eosin and methylene blue, which are toxic to gram-positive organisms.

Additionally, EMB agar is differential because it distinguishes between different types of gram-negative bacteria based on their ability to ferment lactose. Bacteria that ferment lactose will produce acid, leading to color changes in the medium, often resulting in colonies that appear purple or metallic green, indicative of strong fermentation, such as with Escherichia coli. This combination of selective inhibition and differentiation based on metabolic capabilities makes EMB agar a valuable tool in microbiological diagnostics.

The other options do not accurately describe EMB agar. It is not enriched for gram-positive bacteria, nor is it empirical media that supports any bacteria; instead, it specifically supports gram-negative species. Lastly, it does not act as a reducing agent, which is a characteristic of certain other types of media designed to create anaerobic environments.