A 25-year-old man complains of a urethral discharge. You perform a Gram stain on a specimen of the discharge and see neutrophils but no bacteria. Of the organisms listed, the one MOST likely to cause the discharge is:

  •   Treponema pallidum
  •   Coxiella burnetii
  •  Chlamydia trachomatis
  •   Candida albicans