Which of the following characteristics is most commonly associated with Escherichia coli in the context of clinical microbiology?

• A. Spiral-shaped bacterium responsible for syphilis
• B. Gram-positive cocci that forms clusters
• C. Acid-fast bacillus that causes tuberculosis
• D. Gram-negative rod that ferments lactose

Answer: (D)

Verified step by step guidance

1. Identify the morphology and staining characteristics of Escherichia coli (E. coli). E. coli is known to be a Gram-negative bacterium, which means it does not retain the crystal violet stain and appears pink/red after Gram staining.
2. Recognize the shape of E. coli. It is a rod-shaped bacterium (bacillus), not spiral-shaped or cocci (spherical).
3. Understand the metabolic properties of E. coli. It is a facultative anaerobe that ferments lactose, which is a key biochemical characteristic used in clinical microbiology to differentiate it from other Gram-negative rods.
4. Compare the options given: Spiral-shaped bacterium responsible for syphilis refers to Treponema pallidum; Gram-positive cocci that form clusters refers to Staphylococcus species; Acid-fast bacillus that causes tuberculosis refers to Mycobacterium tuberculosis.
5. Conclude that the characteristic most commonly associated with E. coli in clinical microbiology is that it is a Gram-negative rod that ferments lactose.