What type of organisms does Phenylethyl Alcohol Agar inhibit?

Phenylethyl Alcohol Agar (PEA) is a selective growth medium primarily designed to inhibit the growth of Gram-negative bacteria while allowing Gram-positive bacteria to thrive. The inhibitory action is due to the phenylethyl alcohol present in the medium, which disrupts the outer membrane of Gram-negative bacteria, preventing their growth and proliferation. These characteristics make PEA particularly useful for isolating and cultivating different types of Gram-positive microorganisms, such as staphylococci and streptococci, in mixed cultures.

The presence of Gram-negative bacteria typically leads to competition for nutrients and can alter the growth conditions for Gram-positive organisms, making the selective inhibition provided by PEA particularly valuable in microbiological studies. Thus, the answer reflects the medium's role in differentiating between these two broad categories of bacteria based on their structural differences, particularly in their cell wall composition.