Effect of antiphage serum on the virulence of Corynebacterium diphtheriae.

There is little doubt that the toxigenicity of diphtheria cultures is associated with the lysogenic state. Blair (1924) noted that filtrates from toxigenic cultures lysed atoxic cultures of the diptheria bacillus but not the toxigenic cultures, but later investigators were able to isolate certain phages which could lyse toxigenic strains. We now know that, in general, lysogenic cultures are resistant to their own and to related phages, and that susceptibility to a phage does not necessarily indicate that a culture is nonlysogenic and nontoxigenic. Freeman (1951) and Freeman and Morse (1952) produced toxigenic cultures from nontoxigenic strains by incubating the latter with certain phages. Although many of the cells lysed, some were resistant and these yielded cultures which were both lysogenic and toxigenic. However, lysogenization does not necessarily impart virulence in this system. Freeman repeated his experiments, using the same avirulent strain but a different phage filtrate. In this experiment the lysogenic cultures obtained were avirulent. Hewitt (1952a, b; 1954a, b, c), Groman (1953a, b; 1955), Parsons and Frobisher (1951, 1953) and Parsons (1955) haxe studied this problem most extensively and have confirmed the dependence of virulence upon lysogenicity and the conversion of the nontoxigenic cultures to toxigenic ones by the incorporation of a specific bacteriophage. In contrast to the previous studies, the present investigation is concerned with the conversion from toxigenicity to nontoxigenicity rather than with the conversion from avirulence to virulence. In the past, when diphtheria was rampant, it was not uncommon to find avirulent, nontoxigenic cultures in convalescent patients. These patients had been admitted with clinical diphtheria