Studies on Corynebacterium diphtheriae Isolated in Taiwan

In order to analyse the mechanisms of host-parasite relationships in diphtherial infections, 4 strains of Corynebacterium diphtheriae isolated in Taiwan were first compared for their virulence by intradermal test in cortisone-treated and control (non-treated) groups of rabbits. It was found that #74 strain showed much weaker reaction as compared with other strains, i.e. #103, #78 and #69. This difference was apparent even after dilution of the inoculum to 10-1 or 10-2. In the dose-response curve, in which the amount of living bacilli (viable count) was taken into account, such difference in virulence was clearly observed. Therefore, the difference in virulence is not due to the difference in the number of viable bacilli present in each inoculum, but rather to the inherent ability of the individual bacillus itself to survive and produce toxin in the host.In the cortisone-treated groups of rabbits and guinea pigs, the skin reaction was generally markedly weaker than in control groups. The erythema at the site of injection was almost absent, and if present, it was observed to form a ring-form halo around the outer edge of induration. The induration was also less in size and thickness, and ulceration was rarely observed in the cortisone-treated groups.After intradermal injection of diphtheria bacilli, when the animals were not treated with a single injection of antitoxin to prevent premature death, the mortality of the infected rabbits and guinea pigs was not significantly different between the cortisone-treated and control groups. However, the positive rates of re-isolation of the diphtheria bacilli from regional lymph nodes and spleens of rabbits were significantly higher in cortisone treated than in control groups. Thus, the factors of parasite, i.e. inherent potency of the bacilli to survive and multiply in the host and toxin-producing ability, as well as the host factors such as amount of corticosterioids excreted, etc. seem to be the important determinants of diphtherial infection in man.