CHAPTER 19 Reproductive system Disorders 24. List the STD and the organism that a. Chancre causes a b. Vesicle C. Gumma d. Purulent exudate e. Pharyngitis f. Wart Solution A. chancre The exposure of Treponema pallidum, the gram-negative spirochaete bacterium yielding syphilis. Chancres transmit the sexually transmissible disease of syphilis through direct physical contact. These ulcers usually form on or around the anus, mouth, penis, and vagina..