Question

EMB agar is a medium used in the identification and isolation of pathogenic bacteria. It contains digested meat proteins as a source of organic nutrients. Two indicator dyes, eosin, and methylene blue inhibit the growth of gram-positive bacteria and distinguish between lactose fermenting and non-lactose fermenting organisms. Lactose fermenters form a metallic green or deep purple colonies, whereas the non-lactose fermenters form completely colorless colonies. EMB agar is an example of which of the following?
a. a selective medium onlyb. a differential medium onlyc. a selective medium and a chemically defined mediumd. a selective medium, a differential medium, and a complex medium

Answer 1

Answer:

a selective medium, a differential medium, and a complex medium

Explanation:

EMB Agar (Eosin Methylene Blue Agar) is both a selective and differential culture medium that slightly inhibits Gram-positive bacteria and can be used to distinguish bacteria capable of fermenting lactose from those that are unable to ferment this disaccharide. This medium is commonly used for isolation and differentiation of coliforms (i.e., bacteria found in the soil and water samples) and fecal coliforms (bacteria found in the gut and feces samples). In EMB agar, lactose-fermenting-gram-negative bacteria (e.g., E. coli) will form colored colonies, while non-lactose-fermenting-gram-negative bacteria will form colorless colonies (e.g., Salmonella). EMB agar is composed of lactose, gelatin, methylene blue dye and eosin Y dye ( a xanthene dye) .