What is the principle of solid media?

Solid media enables the growth of bacterial colonies for further identification and analysis. The principle is that bacterial colonies are cultivated and identified by streaking them on a medium that solidifies at 37°C. The solid medium is made from agar, an un-branched polysaccharide extracted from red algae species such as Gelidium. Agar 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.