Eosin methylene blue agar (EMB)
Selective/differential media selects for Gram negative organisms by inhibiting the growth of most Gram positive organisms and differentiates by color using Eosin Y and methylene blue pH indicator dyes. Sucrose and lactose are the fermentable carbohydrates which encourage the growth of fecal coliforms and allow for differentiating them.
Strong fermenters of lactose or sucrose will produce dark purple to black colonies. Weak fermenters will produce mucoid pink colonies. colorless colonies indicate non-ferments of lactose and sucrose and are not a fecal coliforms. Escherichia coli (E. coli) produces a green-metallic sheen.
Enterics are facultative Gram negative, rod-shaped bacteria within the intestinal tracts of humans and animals. Coliforms are enterics that ferment lactose. Coliforms in drinking water are used as indicators of possible contamination with disease-causing organisms.
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