FOOD MICROBIOLOGY
MICROORGANISMS IN FOOD
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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bright pink colonies
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cream colonies
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metallic sheen colonies
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yellowish green colonies
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Detailed explanation-1: -EMB agar inoculated with Escherichia coli demonstrates growth with green-metallic sheen colonies.
Detailed explanation-2: -When they are grown in EMB media with both the dyes in the original molar ratio (approximately 6:1), only E. coli forms green metallic sheen. Presence of green metallic sheen is a bit surprising since the EMB media contain no green dye.
Detailed explanation-3: -The colonies of E. coli grow with a green metallic sheen, which is due to the metachromatic property of dyes (eosin and methylene blue in the ratio of 6:1) and the lactose fermenting property of E. coli, which changes the pH of the medium to acidic.
Detailed explanation-4: -Eosin dye combines with methylene-blue indicator to produce a color change when lactose or sucrose is fermented. Lactose-fermenting coliforms, such as Escherichia coli, produce blue-black colonies with a green metallic sheen due to the amide bonding of the dyes in an acid condition.