Based on its composition, eosin-methylene blue agar is classified as what kind of medium?

Eosin-methylene blue (EMB) agar is classified as selective and differential. This classification is important to understand because EMB agar is specifically designed to inhibit the growth of certain bacteria while allowing others, particularly gram-negative bacteria, to grow. The eosin and methylene blue dyes serve as both indicators and inhibitors, making the medium selective for gram-negative organisms.

Additionally, EMB agar differentiates between lactose fermenters and non-fermenters. Lactose fermenters, such as Escherichia coli, produce acid during fermentation, which interacts with the dyes, resulting in a change of color, often leading to a blue-black appearance. In contrast, non-fermenters typically do not change the color of the medium. This property allows lab technicians to differentiate between bacteria based on their ability to ferment lactose.

Understanding the selective and differential nature of EMB agar is crucial for microbiological studies, as it aids in the identification and isolation of specific types of bacteria from mixed cultures, particularly in clinical and environmental samples.