Question

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

A) E. coli forms beta-hemolytic colonies, while P. aeruginosa forms alpha-hemolytic colonies.
B) E. coli shows no hemolysis, while P. aeruginosa exhibits beta-hemolysis.
C) E. coli produces green pigmentation, while P. aeruginosa is colorless.
D) E. coli is catalase-positive, while P. aeruginosa is catalase-negative.

Answer 1

E. coli typically shows no hemolysis on blood agar, while P. aeruginosa can exhibit beta-hemolysis and produce green pigments such as pyocyanin. These characteristics allow one to distinguish between the two on blood agar plates.

Step-by-step explanation:

To distinguish Escherichia coli (E. coli) from Pseudomonas aeruginosa (P. aeruginosa) on blood agar, you can look for specific characteristics of growth and pigmentation. E. coli, a gram-negative enteric bacillus, will typically produce pink colonies on lactose-containing agars such as EMB or MacConkey due to lactose fermentation. This fermentation, however, does not usually manifest as a color change on blood agar. On the other hand, P. aeruginosa, another gram-negative bacillus, is known for its production of distinctive blue-green pigments, such as pyocyanin, and can also produce fluorescence under UV light. When grown on blood agar, P. aeruginosa may exhibit beta-hemolysis, thus clearing the surrounding red blood cells and creating a halo around the colonies.

The correct answer to the question is B) E. coli shows no hemolysis, while P. aeruginosa exhibits beta-hemolysis. E. coli does not typically cause a significant change in the blood agar around its colonies, while P. aeruginosa can produce beta-hemolysis, clearing the blood cells and often accompanied by a greenish pigment due to the pigments it produces.