Selective media contain specific agents that either promote the growth of the target organism or inhibit the growth of non-target organisms. These agents can be:
Antibiotics - to inhibit the growth of susceptible bacteria. Dyes - such as crystal violet or methylene blue, which inhibit certain groups of bacteria. Salts - high concentrations of sodium chloride can inhibit most bacteria except for halophiles. pH Indicators - to differentiate organisms based on their metabolic byproducts.
