Treponema pallidum is the agent causing syphilis. Early syphilis typically presents with a painless indurated genital ulcer with tender inguinal adenopathy. Benzathine penicillin G 2.4 million units IM is the primary treatment; however, doxycycline 100 mg orally twice daily for 2 weeks can be used as an alternative regimen. Diagnosis is based on dark field microscopy or serologic tests (RPR, VDRL, and FTA-ABS). Haemphilus ducreyi is the agent causing chancroid: painful nonindurated irregular genital ulcers and unilateral or bilateral inguinal adenopathy. Diagnosis can be made by culture or clinical features. Chlamydia trachoma causes LGV. It presents as small painful shallow anal or perianal ulcers with inguinal lymphadenopathy that evolves into painful inguinal buboes. Diagnosis is based on serologic tests and culture. Genital warts are often asymptomatic or may cause anal pruritus or scant bright red blood per rectum. Donovanosis, also known as granuloma inguinale, is characterized by painless genital ulcers, which can be mistaken for syphilis. The causative organism, Klebsiella granulomatis, was formerly called Calymmatobacterium granulomatis: prior to that it was called Donovania granulomatis. This reclassification under the genus Klebsiella was a drastic taxonomic change, because it also involved changing the organism's phylum. However, polymerase chain reaction (PCR) techniques using a colorimetric detection system showed a 99% similarity with other species in the Klebsiella genus.