What is the differential agent in EMB?
lactose
EMB (Eosin Methylene Blue Agar) is a selective and differential culture medium used for the isolation and enumeration of bacteria, particularly the gram-negative enteric bacteria, from clinical and non-clinical specimens. EMB contains various ingredients, including eosin, methylene blue, lactose, peptone, and agar.
The differential agent in EMB is eosin Y and methylene blue. These two dyes are added to EMB to help distinguish between different types of bacteria based on their ability to ferment lactose. Eosin Y is a pH indicator that turns black or purple in the presence of acid, while methylene blue is a redox indicator that turns blue or colorless depending on the redox conditions.
The lactose in EMB serves as the carbon source for bacteria, and organisms that ferment lactose produce acidic by-products. Since eosin Y is a pH indicator, it turns dark purple when the pH is acidic, and methylene blue turns blue when the oxygen tension is high. Therefore, lactose-fermenting, gram-negative bacteria such as E. coli, appear as dark colonies with a metallic green sheen on EMB due to the combination of eosin Y and methylene blue. Non-lactose fermenting bacteria such as Salmonella and Shigella do not produce acid, fail to lower the pH of the medium, and therefore, they do not develop a color.
More Answers:
The Everywhere Microbes: Ubiquitous Nature of Microorganisms.Selective and Differential Properties of Eosin Methylene Blue Agar for Enterobacteriaceae Family
EMB Files: The Crucial Role of Embroidery File Formats in Digital Designs and Production