Agar is widely used in microbiology as a solidifying agent in microbial culture media. It is a polysaccharide derived from seaweed and is primarily composed of agarose. Agar is a mostly inert substance, which makes it an ideal material for microbial culture media because it doesn’t interfere with the growth of microorganisms. Agar can solidify media, allowing microorganisms to grow in a solid environment to promote the formation of distinct colonies and enable selective isolation of specific microorganism. It is also used to prepare selective and differential media, which can provide additional nutrients or other chemical substances to promote or inhibit the growth of specific microorganisms selectively. Agar is sterilized by autoclaving and then poured into Petri dishes to cool and solidify, forming the surface for microbial growth.

Agar is commonly used as a solidifying agent in many microbial culture media for the growth and identification of bacteria, yeasts, and molds from various pharmaceutical, environmental, and food and beverage samples.