Which of the following characteristics is most commonly associated with members of the genus Pseudomonas?

• A. They are obligate anaerobes that ferment lactose.
• B. They are Gram-negative, oxidase-positive rods that often produce a blue-green pigment.
• C. They are acid-fast bacilli that cause tuberculosis.
• D. They are Gram-positive cocci that form endospores.

Answer: (B)

Verified step by step guidance

1. Step 1: Identify the genus Pseudomonas and recall its general characteristics. Pseudomonas species are known to be Gram-negative bacteria, which means they do not retain the crystal violet stain during Gram staining and appear pink/red under a microscope.
2. Step 2: Understand the metabolic traits of Pseudomonas. They are aerobic organisms, meaning they require oxygen for growth, and they are oxidase-positive, indicating the presence of cytochrome c oxidase enzyme involved in the electron transport chain.
3. Step 3: Recognize the morphology of Pseudomonas. They are rod-shaped (bacilli), which helps differentiate them from cocci (spherical bacteria).
4. Step 4: Note the pigment production. Many Pseudomonas species, especially Pseudomonas aeruginosa, produce distinctive pigments such as pyocyanin, which is blue-green in color and can be observed in culture media.
5. Step 5: Compare these traits with the other options. For example, obligate anaerobes fermenting lactose, acid-fast bacilli causing tuberculosis, and Gram-positive cocci forming endospores do not match the characteristics of Pseudomonas.