Molecular composition of diphtheria toxoid produced using semi-synthetic and meat extract-based broths

Abstract

The use of semi-synthetic broths for cultivation of Corynebacterium diphtheriae instead of a meat extract-based broth avoids the presence of highly undesirable bovine meat antigens in the diphtheria toxoid. As information on the composition of casein digest-based broths used for the production of diphtheria toxoid is scarce, we have now developed one. The composition of a casein-based medium that supports vigorous bacterial growth as well as high toxin production is described below. The comparative analysis of the toxoids, produced using the meat-based Pope–Lingood and the casein digest-based broths, showed considerable differences in their molecular composition. The variance of weight distribution of toxoid-containing molecular complexes was smaller when the semi-synthetic broth was used. Normal human therapeutic IgG recognizes some of the proteins in the meat-based medium but does not react with any components of the semi-synthetic medium. While precipitation at the isoelectric point of the diphtheria toxoid produced by culturing the C. diphtheriae strain in the semi-synthetic medium resulted in a preparation meeting the requirement for purity (more than 1500 limit floculation Lf/mg protein nitrogen PN), the toxoid produced in the Pope–Lingood broth failed to meet this requirement in some cases, even after a second purification step using ultrafiltration.