Question

Distinguish E. coli from P. aeruginosa on nutrient agar.

A) E. coli forms green colonies, while P. aeruginosa forms pink colonies.
B) E. coli forms lactose-fermenting colonies, while P. aeruginosa does not ferment lactose.
C) E. coli produces a fruity odor, while P. aeruginosa is odorless.
D) E. coli is oxidase-positive, while P. aeruginosa is oxidase-negative.

Answer 1

Option B correctly states that E. coli forms lactose-fermenting pink colonies, while P. aeruginosa does not ferment lactose and will not display this color on lactose-containing media.

Step-by-step explanation:

To distinguish E. coli from P. aeruginosa on nutrient agar, one must consider several cultural characteristics: color, ability to ferment lactose, odor production, and oxidase activity.

Option B is correct; E. coli forms colonies that can ferment lactose, which may impart a pinkish coloration on certain lactose-containing growth media, such as MacConkey agar. This pink color occurs due to the pH change resulting from acid produced by the fermentation process. In contrast, P. aeruginosa does not ferment lactose, resulting in a different coloration.

P. aeruginosa is known for producing a variety of pigments, such as pyocyanin, which is blue-green, and may lead to a characteristic green color under certain conditions, such as on cetrimide agar specifically designed for Pseudomonas species. Additionally, P. aeruginosa is associated with a distinctive grape-like or tortilla-like odor due to 2-aminoacetophenone production, whereas E. coli generally does not produce such a strong odor.

In terms of oxidase activity, option D is incorrect because the oxidase test results are reversed; it is actually P. aeruginosa that is oxidase-positive, while E. coli is oxidase-negative.