What are the properties of agar as a solidifying agent used for the preparation of growth media?

Agar is an unbranched polysaccharide extracted from red algae species such as Gelidium. It serves as an excellent solidifying agent in microbiological media due to its specific melting characteristics and the fact that it lacks nutritional value for most bacteria. Liquid agar solidifies at around 42°C, while solid agar undergoes melting at approximately 100°C. Agar does not dissolve in cold water but becomes soluble in boiling water. This polysaccharide is utilized as a solidification agent in bacterial growth media for several reasons. Firstly, it remains intact as it is not broken down by bacteria. Secondly, it has the unique property of melting at high temperatures and solidifying at temperatures conducive to bacterial growth. Thirdly, it lacks nutrients that can be utilized by bacteria. Solid growth media can be used in different forms, including agar plates, agar deeps and agar slants.