Question

agar a defined or an undefined medinent Provide the reasoning behind your choice and explain wry this formaelation is desinable. 4 In your own words, what are the roles of eosin Y and methylene blue in EMB agar 4 5 Im 6 Think about the results you recorded a. Growth on the EMB agar and NA plates was recorded as "good growth," "poor growth," or "no growth. These are qualitative and, at least for the first two, subjective terms. What did you use to establish what constituted "good grouth? b. Why wouldn't it be advisable to compare grouth of the organisms on each plate to each othert There are at least two answers to this question! 58 MICROBIOLOGY: Laboratory Theory&Application, Brief

Answer 1

3) EMB is an undefined selective/differential medium. It contains aniline dyes, which inhibit the development of Gram-positive bacteria and selecting for Gram-negative bacteria. It also contains lactose which creates the media differential that is based on ability of organisms to ferment lactose. It consists of a dark blue/green to dark purple agar to promote the development of members of the family Enterobacteriaceae.

4) Eosin Y and methylene blue are pH indicator dyes which combine to form a dark purple precipitate at low pH. They inhibit the development of most Gram positive organisms. They forms a dark purple precipitate and absorbed by the cytoplasmic material of the bacterial cells at low pH.

5) lactose acts as fermentable carbohydrate sources. It promotes the development of gram negative fecal coliforms. Lactose fermentation produce a low pH condition which helps the dyes to form the complex and to differentiate the bacteria from the weak fermentors which produce mucoid or pink colonies.