Physical States of Culture Media:

1. Liquid Media: Often called broths, milks, or infusions, these media have a liquid or fluid consistency that allows them to be easily poured or pipetted from one container to another. A liquid medium is usually prepared in tubes, flasks, or bottles and consists of various solutes dissolved in distilled water. Once inoculated, microbial growth can occur throughout this liquid, transforming a transparent medium into a cloudy (turbid) suspension.

2. Solid Media: These media, usually prepared in tubes or Petri plates, provide a firm surface for microbes to grow on or within. Unlike a liquid medium, bacteria dispersed on a solid medium can grow as a continuous layer or as separate colonies. A solid medium is typically prepared by adding a solidifying agent to a liquid medium.

	The bacteria in this Petri plate are growing on nutrient agar. Numerous bacterial colonies can be seen growing on and within this solid medium.
This tube, prepared as a slant, contains nutrient agar. Note the translucent-to-opaque layer of bacteria growing on the surface of this solid medium.

3. Semisolid Media: A medium having more of a “jellylike” consistency is considered a semisolid medium. Unlike a liquid medium that flows freely, this medium cannot be poured. However, to give it less body or firmness than a solid medium, the solidifying agent used in its preparation is added in smaller amounts. One of the useful features of a semisolid medium is it can be used for determining motility.