E Coli 0157:H7 Produces Clear Colonies on MacConkey Agar, While

question 32

Multiple Choice

E. coli 0157:H7 produces clear colonies on MacConkey agar, while common strains of the organism produce pink colonies on this medium. The organism stains pink in the Gram stain. Select the True statement, given this information.

• A) E. coli 0157:H7 is Gram-positive AND is a normal constituent of the intestinal tract.
• B) E. coli 0157:H7 is a normal constituent of the intestinal tract AND does not ferment sorbitol.
• C) E. coli 0157:H7 does not ferment sorbitol AND is Gram negative.
• D) E. coli 0157:H7 does not ferment sorbitol AND is Gram-positive.
• E) E. coli 0157:H7 produces a toxin AND is a normal constituent of the intestinal tract.

---

Definitions:

Aqueous Solution

A mixture in which water serves as the solvent.

pH

A scale used to specify the acidity or basicity of an aqueous solution, correlating to the concentration of hydrogen ions present.

Isoelectric Point

The pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean.

Lowest pH

Refers to the solution with the highest concentration of hydrogen ions (H+), indicating it is the most acidic among a set of given solutions.