EMB agar Only gramnegative bacteria grow on EMB

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, blue-black 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 p. H, is really red at ph 7. 4 and above (basic) and is yellow below p. H 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