The causative agent of syphilis is
- A. a virus
- B. a fungus
- C. a protozoan
- D. the bacterium Treponema pallidum
Explanation
Treponema pallidum is a spirochaete bacterium, which is why syphilis responds to penicillin. Viral STDs such as HIV and herpes cannot be cured with antibiotics, an important clinical distinction.