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In Brilliant Green Agar, the medium is specifically designed to inhibit the growth of certain types of bacteria. The inhibitor in Brilliant Green Agar primarily targets gram-positive organisms, which means that the presence of this agent allows for the selective cultivation of gram-negative bacteria, particularly enteric pathogens.

Brilliant Green Agar works by using a dye that notably suppresses the gram-positive flora, thereby allowing only gram-negative organisms, including coliforms and other enteric pathogens, to grow. This selective inhibition makes it easier to isolate and identify gram-negative bacteria and distinguish them from those that might interfere with the analysis.

Because it inhibits gram-positive organisms, the medium is highly effective for isolating coliforms from fecal samples and determining the presence of enteropathogenic gram-negative bacteria. Thus, the correct conclusion is that the inhibitor targets both coliforms and gram-positive organisms, enabling a focus on the gram-negative species of interest. The mechanism of action underlines the importance of selective media in microbiological diagnostics and research.