**Core Concept**
"Seal finger" and "whale finger" are classic clinical signs associated with erysipelas-like infections caused by *Erysipelothrix rhusiopathiae*, a gram-positive, rod-shaped bacterium. These terms describe the characteristic appearance of skin lesions—seal finger (a deep, painful, swollen finger with a bluish hue) and whale finger (a large, swollen, purplish fingertip)—seen in human infections, especially in cases of cutaneous inoculation.

**Why the Correct Answer is Right**
*Erysipelothrix rhusiopathiae* is the causative agent of erysipelas in humans and animals. It produces a toxin that leads to vascular damage and inflammation, resulting in the hallmark "seal finger" and "whale finger" presentations. These signs are due to localized tissue necrosis and hemorrhage, with the lesions often appearing on fingers or toes after trauma. The organism is commonly found in poultry and pigs, and human infections occur via puncture wounds or direct contact.

**Why Each Wrong Option is Incorrect**
Option A: *Listeria* causes listeriosis, which presents with meningitis, sepsis, or fetal infection, not characteristic finger lesions.
Option C: *Corynebacterium* species cause impetigo or cutaneous abscesses, but not the specific "seal finger" or "whale finger" signs.
Option D: *Treponema* (e.g., *T. pallidum*) causes syphilis, with lesions like chancres or chancroid, not these specific finger signs.

**Clinical Pearl / High-Yield Fact**
"Seal finger" and "whale finger" are **pathognomonic signs of *Erysipelothrix rhusiopathiae* infection** in humans—especially after trauma—and should prompt immediate antibiotic therapy and source control.

✓ Correct Answer: B. Erysipelothrix