Properties of Strains of Corynebacterium diphtheriae Obtained from Various Parts of the United States

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Abstract
A study of strains of C. diphtheriae isolated from healthy casual carriers, persons with clinical diphtheria, and the familial or other immediate contacts of the latter, has been conducted in collaboration with national, State and local health agencies in the U. S. A collection of pure cultures (about 2,000), representing 17 States from New York to California and Minnesota to Mississippi, has been carefully studied and described and is maintained in vacuo in the material in which originally isolated. It was shown through carrier surveys that any type of diphtheria bacillus, e.g., gravis or mitis, virulent or avirulent, may predominate and at times may be the only type present in some communities but not in others. This phenomenon may be extremely localized or very general, and under present conditions in the U. S. conclusions in regard to type prevalence or rates are not valid beyond the confines of a county or State, and often a town or village. It appears that the mitis-like type of C. diphtheriae is about 10 times as common as the gravis-like type in the U. S., and since only about 1 in 10 of the latter is of the true gravis type, probably not more than 1 strain of C. diphtheriae in over 100 in the U. S. is of the virulent and genuinely gravis type. The gravis type of C. diphtheriae is not an important health problem in the U. S. at present. There are certain advantages in the use of 7-14-day-old chicks for testing the virulence or toxicogenicity of diphtheria bacilli and for measuring the potency of toxin. Mice are highly susceptible to the intra-cerebral injn. of both virulent and avirulent cultures of C. diphtheriae, although highly resistant to these cultures when injd. subcut. or intraperit.