Final answer:
New York City (NYC) agar is the medium that is both selective and differential for Gardnerella vaginalis. It supports the growth of G. vaginalis and provides visual differentiation among bacterial species.
Step-by-step explanation:
The medium that is both selective and differential for Gardnerella vaginalis (G. vaginalis) is New York City (NYC) agar.
Selective media, such as NYC agar, inhibit the growth of unwanted microorganisms while supporting the growth of the specific organism of interest, in this case, G. vaginalis.
Differential media make it possible to distinguish among different bacterial colonies based on color changes that result from the interaction of bacterial enzymes with differential substrates in the medium.
For example, EMB agar and MacConkey agar are known to utilize lactose fermentation to distinguish between lactose fermenters, which produce colored colonies, and non-lactose fermenters, which produce colorless colonies.
However, for the isolation and identification of G. vaginalis, NYC agar is the appropriate medium because it is tailored to support the growth of this specific bacterium while also providing visual differentiation among bacterial species.