What are the selective agents in EMB?
eosin and methylene blue
EMB (Eosin Methylene Blue) agar is a selective and differential medium commonly used for the isolation and differentiation of Gram-negative bacteria, particularly Enterobacteriaceae.
Selective agents in EMB agar include:
1. Eosin Y: It is a pH indicator that gives the EMB agar its characteristic metallic sheen. Eosin Y inhibits the growth of Gram-positive bacteria by promoting an acidic environment.
2. Methylene blue: It helps to inhibit the growth of Gram-positive bacteria. It also helps to differentiate between lactose fermenters and non-fermenters.
3. Lactose: It is a carbohydrate that encourages the growth of lactose fermenting bacteria. Lactose fermenting bacteria will produce acid as a by-product of fermentation, which changes the agar’s pH and produces a characteristic color change. Non-fermenting bacteria will not produce any color change.
Overall, EMB agar’s selective agents inhibit the growth of Gram-positive bacteria and encourage the growth of Gram-negative lactose fermenters.
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