True about corynebacterium diphtheria includes all of the following except:

Ans. (d) Toxigenicity is mediated by chromosomal change "Corynebacteriophage beta carries the structural gene (tox+) encoding diphtheria toxin and a family of closely related corynebacteriophage are responsible for toxigenic conversion of tox- C.diphtheria to tox+ phenotype." Elek's gel precipitation test is in vitro test for toxin detection.