Q. A 25-year-old male presents to your clinic with symptoms of burning with urination and discharge from his penis. He has no other significant medical history and is not currently taking any medications. The patient reports having multiple sexual partners, and denies the use of condoms or other barrier protection. On physical examination, his temperature is 37.2 degrees Celsius (98.9 degrees Fahrenheit), blood pressure 120/75 mm Hg, heart rate 70/min, respiratory rate 18/min. The patient's genital assessment demonstrates a penis of normal size and shape with no visible deformities or curvatures. The glans of the penis is rounded with no discoloration, and the shaft of the penis is smooth, without any lumps or bumps. A small amount of yellowish discharge is noted at the urethral meatus with a moderate amount of erythema present. The patient has been circumcised, and the circumcision scar is clean and dry. Palpation of the patient’s testicles reveals normal size and consistency, with no lumps or masses felt. The epididymis is noted to be tender, and the scrotum is without any redness, tenderness, swelling or masses. You suspect a sexually transmitted organism as the likely cause of the patient’s symptoms. Which of the following tests would be most helpful in confirming your suspicion?