This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
[{'content': 'Diphtheria toxin is produced only by those strains of C. diphtheriae that are \nSelect and explain. \nA. Glucose fermenters, B. Sucrose fermenters, C. Lysogenic for b-prophage, D. Of the mitis strain', 'role': 'user'}, {'content': 'Answer: C \nExplanation: All toxigenic strains of Corynebacterium diphtheriae are lysogenic for b-phage carrying the Tox gene, which codes for the toxin molecule. The expression of this gene is controlled by the metabolism of the host bacteria. The greatest amount of toxin is produced by bacteria grown on media containing very low amounts of iron.', 'role': 'assistant'}]