Selective Differential Media

Selective Differential Media Selective
Media
Population
Ingredients
Selected
(determines
what grows
)

MSA(p.
105)

MAC(p.
117)alphale
teathletics
@yahoo.co
m (

Salt
NACL
7.5%
­
makes the medium selective by inhibiting the growth of most bacteria, but allowing salt­ tolerant (Halophile
) staphylo cocci to grow ­ allows staphylococc i to grow b/c they are salt tolerant ­ only disease causing staphylococc i ferment the sugar mannitol, so non disease causing staphylococc i will grow but not change the color and dieses causing staphylococc i will grow and change the color of the media alphaleteat ­selects for hletics@ya the hoo.com identification
(bacteria, of gram but negative allowing enteric (fecal many gram coliform negatives bacteria that including live w/I the coliforms intestines of to warm

Differential
Ingredients
(determines what the microbes that are growing look like Color change and Why

The sugar
Mannitol and the pH indicator Phenol red

Mannitol fermenters release acid into the medium, which turn the phenol red in the medium around the colony yellow i

The sugar lactose and the pH indicator Neutral red
– differentiate between non lactose fermenters and lactose fermenters The production of acid from lactose fermentation causes the colonies of lactose fermenters to appear
Pink
distinguishing it from other gram negative bacteria

grow

EMB(p.
111)

blooded animals) organisms which grow and form pink colonies
­ gram negative non lactose fermenting bacteria grow as colorless colonies
­ gram positive bacteria grow poorly do to inhibition by bile and crystal violet
The two
Selects for dyes the together identification
Eosin and of gram methylene negative blue make lactose the media fermenting selective bacteria by ­ is
inhibiting