All are true regarding diphtheria toxin except

Virulent strains of diphtheria bacilli produce a very powerful exotoxin. The pathogenic effects of the bacillus are due to the toxin. Almost all strains of gravis and intermedius are toxigenic. The toxin is extremely potent and the lethal dose for a 250 g guinea pig is 0.0001g. The toxin has a special affinity for ceain tissues such as the myocardium, adrenals and nerve endings. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 240