## **Core Concept**
Spirochaetes are a group of spiral-shaped bacteria that belong to the phylum Spirochaetes. They are known for their unique morphology and include pathogens that cause several significant human and animal diseases. The question requires the identification of which options are classified as spirochaetes.

## **Why the Correct Answer is Right**
The correct answer includes options A, B, and E.
- **Syphilis** is caused by *Treponema pallidum*,
- **Leptospira** is a genus of spirochaetes that cause Leptospirosis,
- **Borrelia** is another genus of spirochaetes, which includes species causing Lyme disease (*Borrelia burgdorferi*) and relapsing fever.

## **Why Each Wrong Option is Incorrect**
- **Option C: Mycoplasma** - Mycoplasmas are a group of bacteria that lack a cell wall and are not spirochaetes; they are among the smallest living cells.
- **Option D: Brucella** - Brucella species are Gram-negative bacteria that cause Brucellosis but are not classified as spirochaetes; they belong to the family Brucellaceae.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that spirochaetes are spiral-shaped bacteria, and examples of diseases caused by them include syphilis (*Treponema pallidum*), Lyme disease (*Borrelia burgdorferi*), and Leptospirosis (*Leptospira*). These pathogens are often identified through their unique microscopic appearance and are targeted by specific antibiotics.

## **Correct Answer:** A, B, E.