The Adaptation in Vitro of Diphtheria Bacillus to Specific Antitoxin.

Observations on the transmutation of toxic and virulent strains of B. diphtheriae into atoxic and non-virulent varieties by means of cultivation in a medium containing either normal serum or specific antitoxin have been reported by Bernhardt, 1 Levinthal 2 and, after the completion of the present work, by Becker. 3 In this paper, which deals with the same problem, the relation between toxin production and virulence of the adapted diphtheria strain was given more attention than has been accorded to it in the past. At the same time the flocculating properties of the atoxic filtrate of an adapted culture when brought in contact with the specific antitoxic serum, were studied in view of the doubt which has recently been expressed in the literature on the specific nature of the flocculation occurring in neutral mixtures of bacterial toxins with their respective antitoxins (Schultz 4 ).

Two diphtheria strains, the Park-Williams No. 8 and a recently isolated strain D X, which differed widely under normal standard conditions in toxigenicity and virulence, were employed. The P. W. strain produced a powerful toxin with an m.f.d. of 0.002, while the filtrate of the D × strain obtained under the same conditions yielded a low grade toxin with an m.f.d. of 0.02 (30 cc. of sugar-free veal infusion broth with 0.2% dextrose incolated with one loop of a 24-hour Loeffler slant culture and incubated for 5 days at 35-36° C.). On the contrary, the P. W. strain was fatal for guinea pigs only in amounts as large as 1/4 Loeffler slant, while the D × strain was highly virulent, 1/20 slant killing a guinea pig within 31 hours. The antiserum was a nonpreserved diphtheria antitoxic horse serum with a titer of 350 units per cc. Normal horse and tetanus antitoxic horse sera were run along for purposes of control.