On the difference between the toxigenicity and infectivity of C, diphtheriae.

Three strains were chosen in this experiment. Strain 10-19 invariably developed a severe disease and strain 8-14 a mild case. Strain PW-8 was chosen because of its high toxigenicity in the fluid media, but it caused very slight clinical symptoms by conjunctival method. Exp. 1. Bacterial suspensions of three strains were prepared by washing twice fresh cultures from serum agar plates. To test the lethal activity, adequate two-fold serial dilutions of the suspensions were injected into guinea pigs (350-450 g) subcutaneously in a volume of 1 cc. DRM was determined by intracutaneous injection of serial dilutions in a volume of 0.1 cc on the back of guinea pigs. The sensitivity of the skin to diphtheria toxin was checked by intracutaneous injection of 10 to 80 fold dilutions of Schick toxin. Infection at the conjunctiva was carried out by the same method as before by using a bacterial suspension of 30 mg per cc by wet weight (Murata et al., 1959). The results are shown in Table 1. Autopsy of animals which died showed typical changes of intoxication in all cases irrespective of the methods of infection. It was then examined whether the intoxication after injection of cell suspension was caused by the toxin involved in the original cells or produced in vivo. The suspensions of washed cells of strain 10-19 were injected subcutaneously to two groups of guinea pigs. One group of them received simultaneously the intravenous injection of 6 mg erythromycin and then the subcutaneous injection of 2 mg of the drug for subsequent 4 days. Almost all animals of the control groups (9/10) (without erythromycin) died within 3 days after injection, while animals of erythromycin group survived for a period during which they were treated with the drug but all died after the treatment was discontinued (Table 2). This fact and the pathological changes on autopsy suggest that the intoxication might be due to the toxin produced de novo after injection. In other words, the injection method shows the toxigenicity in vivo. Toxigenicity in vivo was almost equal with three strains by intracutaneous or subcutaneous method, while significant differences were shown in the conjunctiva) method. These results suggest that there are fundamental difference between the infectivity by mucous membrane method and the toxigenicity by the injection. Exp. 2. Mueller (1941) reported that the virulent gravis type strain was able to produce a high titer toxin in the medium with high iron concentration. Then an ex-