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Refractometric and Chemical Study of Diphtheria Toxin

From the Connaught Laboratories, University of Toronto

Abstract

The growth of a Park-Williams No. 8 strain on broth is accompanied by a marked drop of the refractive index of the medium.

The interdependence of growth and toxin production finds expression in a close relationship between Lf-formation and the refractometric changes. For a given strain (P.W. 8) and a definite type of medium, the refractometric difference between control broth and toxin may serve as an approximate measure of the number of Lf-units formed.

Between the sixth and tenth days of incubation (32°C.) the protein, built up by the microörganism and given off into the originally protein-free medium, increases faster than the Lf-units. This fact suggests that only part of this protein should be identified as toxin.

The toxicity (max. 6000 M.L.D.) begins to fall off before the maximum Lf-value (78) is reached. No accurate and constant ratio MLD/Lf can therefore be established.