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

EMB agar is an example of a selective medium, a differential medium, and a complex medium, as it contains ingredients that inhibit gram-positive bacteria and distinguish lactose fermenting organisms by colony color.

Step-by-step explanation:

EMB agar is a medium used in the identification and isolation of pathogenic bacteria. The presence of digested meat proteins provides a source of organic nutrients, making it a complex medium. It also contains two indicator dyes, eosin and methylene blue, which inhibit the growth of gram-positive bacteria, thus serving as a selective medium. Furthermore, these dyes allow for the distinction between lactose fermenting and non-lactose fermenting organisms, classifying EMB agar as a differential medium as well. Lactose fermenters display metallic green or deep purple colonies, while non-lactose fermenters form colorless colonies. Therefore, EMB agar is an example of option (d) a selective medium, a differential medium, and a complex medium.

Answer 2

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

Step-by-step 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) .