Question

1. a metallic green sheen on emb indicates: a. no fermentation b. weak acid production c. strong lactose fermentation d. protein hydrolysis 5. hek agar is used to detect organisms that: a. ferment glucose b. produce indole c. produce h₂s and ferment sugars d. are oxidase positive 6. on hek, black - centered colonies suggest: a. glucose fermentation b. sulfur reduction c. salt tolerance d. capsule formation

Explanation:

1. Eosin - methylene blue (EMB) agar is a differential medium. Strong lactose - fermenting bacteria produce a large amount of acid, which reacts with the dyes in EMB to give a metallic green sheen.
2. Hektoen enteric (HEK) agar contains indicators and substrates to detect organisms that produce hydrogen sulfide ($H_2S$) and ferment sugars.
3. On HEK agar, black - centered colonies are due to the production of $H_2S$, which is a result of sulfur reduction.

Answer:

1. C. Strong lactose fermentation
2. C. Produce $H_2S$ and ferment sugars
3. B. Sulfur reduction