Question

help please

What type(s) of bacteria are favored to grow on eosin methylene blue (EMB) agar? Select one: O a Gram positive bacteria that can undergo anaerobic respiration. O b. Gram negative bacteria that can ferment glucose and/ or lactose, O c. Only those bacilli that can utilize citrate as a main carbohydrate source. O d. All Bacteria would grow equally well A bacterial species grows on a MacConkey agar plate, and the colonies have dark red color with hazy precipitation around. This bacterium must be capable of: Select one: a. Fermenting lactose to produce lots of acidic by-products. ob Fermenting mannitol to make acidic by-products, which lowers the pH of the EMB agar c. Utilizing citrate as a main carbohydrate source for growth od secreting exoenzymes that make urea.

Answer 1

Question 1

Answer: Eosin methylene blue (EMB) agar media is a selective media for gram negative bacteria. It contain two stains-Eosin and methylene blue. The dyes in the media are toxic to gram positive bacteria and hence their growth is inhibited. EMB agar media also differentiates the bacteria based on their ability to ferment lactose. Bacteria that ferment lactose produces acids that enable then to uptake the dye. Hence, lactose fermenting bacteria appear purple black. Lactose non-fermenting bacteria increases the pH of the medium, leading to non-absorption of the dye. Lactose non-fermenters appear colorless. Hence, option b is the correct answer and option a and d are incorrect. EMB medium does not contain citrate and hence option c is incorrect.

Question 2

Answer: MacConkey agar is a selective and differential media that selectively isolates gram negative bacteria and differentiates them based on their ability to ferment lactose. The crystal violet dye and bile salts in the media inhibits the growth of the gram positive bacteria, leading to selectively isolation of gram negative bacteria. Bacteria that is able to ferment lactose produces acid that lowers the pH of the agar and precipitates bile salts. This leads to pink/dark red colonies with hazy appearance around it. Hence, option a is the correct answer. MacConkey agar medium does not contain mannitol and citrate as a media component. The color of the colonies is not due to urea synthesis by exoenzyme. Hence, option b, c, and d are the incorrect answer.