What is the role of phenylethyl alcohol in media?

Phenylethyl alcohol in media serves primarily to inhibit the growth of gram-negative bacteria while allowing gram-positive bacteria to thrive. This compound alters the permeability of gram-negative bacterial cell membranes, making it more difficult for these organisms to survive and reproduce under certain conditions. As a result, the presence of phenylethyl alcohol is beneficial in selective media formulations where the goal is to cultivate gram-positive bacteria, such as Staphylococci and Streptococci, while suppressing unwanted gram-negative contaminants.

In contrast, the other choices do not accurately reflect the function of phenylethyl alcohol in microbiological media. It does not inhibit gram-positive organisms or stimulate growth of either type. Instead, its specificity is oriented towards suppressing gram-negative growth, thus providing a selective environment conducive to gram-positive bacteria.