Question

dyes, such as phenol red or methylene blue used in differential media? Why are dyes, such as A. to inhibit motility B. to stain microbes C to kill bacteria D. to see microbes to detect pH changes due to metabolism What is the purpose of differential medias to encourage growth of the desired bacteria B to isolate few bacteria to observe metabolism of the bacteria D. to stain bacteria E to determine motility 10 Why does Staphylococcus aureus turn yellow on MSA? A the microbes have fermented lactose 8. the microbes are salt-tolerant ċ the microbes have fermented mannitol D. the microbes are resistant to eosin and methylene blue E the microbes are resistant to phenol red 11. EMB has the dye eosin dye to inhibit the growth of some bacteria, whereas MSA has A mannitol B. salt Cmethylene blue D. lactose E phenol red 12. What is the definition of selective media? A They have a wide variety of fuel supplies available and support the growth of most types of bacteria. B. They have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms. C. They incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another. D. They incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies 13. What is the purpose of adding eosin and methylene blue to eosin-methylene blue (EMB)agar? A. They inhibit the growth of gram-negative organisms. B. They are pH indicators that turn blue or purple when lactose is fermented C. They directly inhibit the growth of lactose non-fermenters. D. They have dyes that precipitate on the surface of acid-producing colonies of enteric lactose fermenters creating a metallic green sheen. E They permit the differentiation of bacteria based on their ability to ferment mannitol.

Answer 1

Ans-8- dye like phenol red in differential media are used to detect the change in pH that occurs due to production of acid when bacteria ferment the sugars.

Option E is correct

Ans-9- the differential media is used to identify the specific desired microorganisms visually in media from the closely related other microorganisms.

Option B is correct

Ans-10- MSA contains phenol red as a pH indicator. When staphylooccus ferment the mannitol it produces acid that changes the color of media upon reacting with phenol red.

Option C is correct

Ans-11- MSA has salt that inhibit the growth of other bacteria accept staphylococci.

Option B is correct

Ans-12- selective media contains the agent that inhibit the growth of one particular type of bacteria while inhibit the growth of other type of bacteria, hence allow to isolate specific bacteria.

Option C is correct

Ans-13- EMB is used for the isolation of faecal coliforms which are lactose fermenters. When lactose is fermented by the bacteria it produces acid which forms a dark purple color compex. Bacteria like E.coli produces some metallic green color as well due to change in pH upon lactose fermentation.

Option B is correct