BIOS 111 Lecture Notes - Lecture 12: Crystal Violet, Peptide, Meat Extract
Document Summary
Defined media: we know everything in there. Complex media: easy to make, but you don"t know the exact chemicals in there. You don"t know precisely what"s in there. Nutrient agar: peptone, beef extract, sodium chloride. Yeast extract: you have yeast molecules, but you don"t know what is all in there because you have the whole molecules and all that come with it. Same goes for beef extract; you just take a part of the organism and get everything that comes with it. Selective: we design components in the media so only gram-negative bacteria can grow in it and not gram-positive. Differential: colonies are growing, but you can differentiate them by morphology and color. Macconkey"s agar was made for o157:h7 strain of e. coli. His agar distincted o157:h7 from all other strains of e. coli. 0. 001g crystal violet (toxic to living cells) Bile salts and crystal violet are the selective components. They inhibit the growth of gram-positive bacteria.
