This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
True about corynebacterium diptheria includes all of the following except : 
Select and explain. 
A. Deep invasion is not seen, B. Elek’s test is done for toxigenicity, C. Metachromatic granules are seen, D. Toxigenicity is mediated by chromosomal change
D: Toxigenicity is mediated by chromosomal change
Answer: D: Toxigenicity is mediated by chromosomal change 
Explanation: “Corynebacteriophage beta carries the structural gene (tox + ) encoding diptheria toxin and a family of closely related corynebacteriophage are responsible for toxigenic conversion of tox – C.diptheria to tox + phenotype.”

Elek’s gel precipitation test is in vitro test for toxin detection.