Antigenic Relationships of Diphtheria Bacilli and Derived Variants

Abstract

The antigenic relationships between diphtheria bacilli and certain derived variants have been investigated by means of the complement fixation reaction.

Two strains of virulent diphtheria bacilli, No. 19 and Park No. 18 and avirulent variant strains derived from these strains were used in the experiments, and in addition, a strain of C. hofmanni.

Two of the variant strains, Park No. 8 phage a and Park No. 8 phage b, were derived from young cultures of Park No. 8 to which specific bacteriophage had been added. Four of the variant strains were derived in various ways from the No. 19 culture and are designated as follows: 19 ‘antiserum’, derived from culture in broth containing homologous antiserum, 19 ‘broth 45°C.’ from broth culture incubated at 45°C; 19 ‘LiCl’, from culture in broth containing 0.5% lithium chloride; 19 ‘phenol’, from culture in broth containing 0.1% phenol.

These variant organisms were found to be stable in type, grew very slowly in broth, and were completely lacking in fermentative ability. The variant colony was much smaller than the typical colony of diphtheria colony. Microscopically, the variant organisms were hardly distinguishable from the parent organisms. Usually they stained more solidly, but many barred and granular forms were observed.

Sera taken from some of the rabbits before immunization failed to fix complement except when large amounts of serum were used. The course of immunization consists of 8 to 10 injections of heat-killed organisms. The sera obtained were inactivated by heating them at 60-62 °C. for 30 minutes.

The sera were used in 4 amounts: 0.025, 0.012, 0.006, and 0.003 cc. All antigens were used in such an amount that 4 times that amount was not anticomplementary. The smallest amount of serum giving a strong reaction with the homologous antigen was used as a base and the reactions in this amount with other antigens is reported in the tabulation.