Selective and Differential Media
- Selective: agar has ingredients that prevent growth of some bacteria, permit only certain kinds of bacteria to grow.
ex) Eosin and methlyne blue prevent gram positive bacterial growth
pseudomonsas = gram negative (growing
streptococcus= gram positive (not growing)
ex) Manitol salt agar: has salt in VERY high concentration
bacteria can not grow easily because salt concentration is too high
staph grows on skin {grew on plate}
strep grows in throat {didn't grow on plate}
- Differential: has ingredients that allow you to see metabolic differences between kinds of bacteria that you grow on it
ex) Manitol salt sugar: has very high salt concentration AND Manitol
manitol is a sugar that some bacteria can ferment plus methylred: dye that changes from red to yellow at low pH
ex) EMB
< Eosin: pH indicator (changes from pink to green at low pH levels)
< Lactose: can be fermented by some bacteria; producing an acid byproduct, but not by other bacteria.
Kassie Hein
page revision: 2, last edited: 17 Sep 2009 23:24