![]() ![]() Levine modification contains 10g of lactose (twice as in EMB agar) and contains no sucrose. The composition of EMB agar and modified EMB agar (Levine EMB) agar differs slightly. ![]() Peptic digest of animal tissue serves as a source of carbon, nitrogen, and other essential growth nutrients. Non-lactose fermenters, increase the pH of the medium by deamination of proteins and produce colorless or light pink colonies.Įosin Y and methylene blue are pH indicator dyes that combine to form a dark purple precipitate at low pH they also serve to inhibit the growth of most Gram-positive organisms.Organisms that are slow lactose-fermenters, produce less acid, and the colonies appear brown-pink.This metallic green sheen is an indicator of vigorous lactose and/or sucrose fermentation ability typical of fecal coliforms. Lactose-fermenting gram-negative bacteria acidify the medium, which reduces the pH, and the dye produces a dark purple complex usually associated with a green metallic sheen.Differentiation of enteric bacteria is possible due to the presence of the sugars lactose and sucrose in the EMB agar and the ability of certain bacteria to ferment the lactose in the medium. EMB agar contains sucrose and lactose, utilized as fermentable carbohydrates substrates, which encourage the growth of some gram-negative bacteria, especially fecal and non-fecal coliforms. ![]()
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