∞ generated and posted on 2021.05.03 ∞

Microbial growth media that contains no agar or other thickening agents.

Broth is literally broth, as equivalent more or less to liquid medium from which soup is made, though as with soup broth, ingredients can vary depending on use. The distinction here is solely that broth as a microbiological growth medium is formulated to optimize microbial growth in terms of nutrients and other factors rather than necessarily in terms of how it tastes to a diner.

Broth contrasts with buffers where the former contains organic nutrients (particularly carbon and energy sources) whereas the latter does not.

Physically, broth has the characteristic that it can be readily mixed, allowing for increased homogeneity as well as more rapid penetration of materials into the medium, most notably oxygen but also microorganisms themselves. Broth also can be described as a relatively spatially unstructured environment and well-mixed broth is the microbiological equivalent of an unstructured environment.

Most uninoculated broth media is crystal clear though this clarity can occur also due to organism settling to the bottom of the test tube or flask.

In unstructured environments, movement is unencumbered and in fact the potential for two things to encounter each other is similar no matter where the two things are located at a given moment within an environment relative to each other.

Broth media is called broth for the same reason that chicken, beef, or vegetable broth is called broth. That is, the first growth media for microorganisms were often boiled down foods and thus early on in microbiology broth really was broth. Indeed, broths today as used in the microbiology laboratory often are still consists mostly of boiled down food.

A broth tube contains liquid media that often though not always is crystal clear. Cloudiness (turbidity) for most media is a sign of contamination and such broth tubes should be discarded (unless the media is intentionally cloudy, such as milk-based media).