EMB agar
Only gram-negative
bacteria grow on EMB
agar. (Gram-positive
bacteria are inhibited by
the dyes eosin and
methylene blue added to
the agar.) Based on its rate
of lactose fermentation, E.
coli produces dark, blueblack colonies with a
metallic green sheen on
EMB agar.
Growing on EMB Agar
Enterobacter aerogenes
Nutrient Agar
Micrococcus luteus
Pseudomonas aeruginosa
Mannitol Salt Agar
Mannitol salt agar is both a selective and differential
growth medium. It is used to differentiate pathogenic
Staphylococcus species from nonpathogenic
members of the genus Micrococcus.
Fermentation of mannitol: This medium contains an
indicator, phenol red. The indicator is a pinkish-red
at neutral pH, is really red at ph 7.4 and above
(basic) and is yellow below pH 6.8 (acidic). An
organism can either ferment (metabolize) mannitol
or not and this will be indicated by a color change
on the MSA plate--which makes this a differential
test.
1. S. aureus
Salt tolerance +
Mannitol fermentation +
(yellow)
2. M. luteus
Salt tolerance Mannitol fermentation -
2. S. epidermidis
Salt tolerance +
Mannitol fermentation -
Staphylococcus aureus
Growing on Mannitol Salt
Agar.
Staphylococcus epidermidis Growing on
Mannitol Salt Agar