The toxigenicity of C.diphtheriae is due to:

The toxigenicity of C.diphtheriae is due to beta phage. Diphtheria Toxin production depends on : Phage coded: Diphtheria Toxin is coded by b corynephage carrying tox gene-toxigenic. Iron concentration: toxin production depends on optimum iron concentration (0.1 mg per liter). DT repressor gene (DtxR)- iron dependent negative regulator of Diphtheria Toxin production and iron uptake in C.diphtheriae. Biotypes: 3 biotypes with their toxigenicity is as follows : All strains of gravis, 95-99% strains of intermedius, 80-85% of mitis strains are toxigenic. However, toxins produced by different biotypes are antigenically similar.