A sexually active male presents with oral lesions consistent with syphilis. Which organism is most likely responsible?

Syphilis is caused by the spirochete Treponema pallidum. Oral manifestations include: primary syphilis — painless chancre (usually on lips, tongue, or tonsils); secondary syphilis — mucous patches (flat, whitish, painless, highly infectious), condylomata lata, and maculopapular rash including palms and soles; tertiary syphilis — gummas (granulomatous lesions) affecting the palate and tongue. Syphilis is a reportable sexually transmitted infection. Neisseria gonorrhoeae can cause pharyngeal/oral infection but not the described syphilitic lesions. Candida causes pseudomembranous thrush. HSV causes vesicles/ulcers.