Toxin-Production As Related to the Clinical Severity of Diphtheria

Summary C. diphtheriae elaborates relatively little toxin in the presence of concentrations of iron present in the throat. In the average case of mild diphtheria comparatively small amounts are probably formed. Severe (gravis) diphtheria may result from infection with strains able to produce more toxin in the presence of abundant iron. Three non-gravis types have been shown to produce approximately 3 MLD/ml under these conditions, whereas a gravis type produced 40 MLD. It is probable that a difference of this order is sufficient to explain observed variations in the clinical severity of the disease.