What is the main distinction between selective and differential media?

The main distinction between selective and differential media lies in their specific functions and applications in microbiological studies. Selective media are designed to inhibit the growth of certain bacteria while allowing others to grow. This is particularly useful when isolating a specific species from a mixed culture. For example, a selective medium might be used to grow only Gram-negative bacteria while preventing Gram-positive bacteria from growing.

On the other hand, differential media are used to differentiate closely related organisms based on their biochemical properties. They allow various types of bacteria to grow but contain substances that cause certain bacteria to appear different from others. This differentiation can be seen through color changes in the media or colony morphology, which aids in the identification of bacteria based on specific metabolic activities.

Therefore, option A accurately captures the essence of these two types of media: selective media inhibits the growth of unwanted bacteria while allowing desired ones to thrive, and differential media reveals biochemical differences among species, facilitating their identification.