This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
[{'content': 'True about corynebacterium diphtheria is all except \nSelect and explain. \nA. Diptheriae invasion is not seen, B. Eleks test is done for toxigenicity, C. Metachromatic granules are seen, D. Toxigenicity is mediated by chromosomal change', 'role': 'user'}, {'content': "Answer: D \nExplanation: Toxigenicity of the diphtheria bacilli depends on the presence in it of corynephages which acts as the genetic determinant controlling toxin production. The diphtheria toxin acts by inhibiting protein synthesis. Specifically, a fragment B heparin binding and fragment A inhibits polypeptide chain elongation in the presence of nicotinamide adenine dinucleotide by inactivating the elongation factor EF-2. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 240", 'role': 'assistant'}]