A 27-year-old woman presents to the gynecology clinic with complaints of thin, grayish-white vaginal discharge and a strong “fishy” odor, particularly after sexual intercourse. She denies itching, burning, or systemic symptoms. A whiff test is positive, releasing a fishy odor upon the addition of potassium hydroxide (KOH) to vaginal secretions. The vaginal pH is 5.5, and microscopy of a wet mount reveals clue cells. Which of the following correctly describes the predominant organism that causes this disorder?