‘Syphilis’, a sexually transmitted diseases is caused by

The correct option is Treponema pallidum.

Step-by-Step Explanation:

1. Understanding Syphilis:
Syphilis is a highly contagious sexually transmitted infection (STI) that can cause serious health complications if left untreated. It progresses through primary, secondary, latent, and tertiary stages, each characterized by distinct clinical symptoms such as chancres (painless sores), skin rashes, and potentially severe damage to the heart, brain, and other organs in its late stages.

2. Identifying the Causative Agent:
The disease is caused by a specific spiral-shaped bacterium (spirochete) known as Treponema pallidum (specifically the subspecies pallidum). This bacterium is motile and is typically transmitted through direct contact with an infectious sore during sexual activity.

3. Analyzing the Other Options:
• Vibrio: Bacteria belonging to this genus (such as Vibrio cholerae) are comma-shaped and primarily cause waterborne gastrointestinal diseases like cholera, not sexually transmitted infections.
• Pasteurella: Members of this genus (like Pasteurella multocida) are zoonotic bacteria often transmitted through animal bites or scratches, causing wound infections.
• Leptospira: This is another genus of spirochetes, but it causes leptospirosis, an infectious disease transmitted through water or soil contaminated with the urine of infected animals.

Therefore, among the given choices, Treponema pallidum is the unique bacterium responsible for causing syphilis.