A 34-year-old man who works as a carpenter presents with symptoms of jaw discomfort, dysphagia, and pain as well as stiffness in his neck, back, and shoulders. On examination, he is unable to open his jaw, his proximal limb muscles are stiff as is his abdomen and back, but the hands and feet are relatively spared. He occasionally has violent generalized muscles spasms that cause him to stop breathing, but there is no loss of consciousness. A clinical diagnosis is made and he is treated with antibiotics, antitoxin, and diazepam as well as muscle relaxants for the spasms.For the above patient, select the most likely infecting organism.