I. A Coccoid Form ofC. diphtheriaeSusceptible to Bacteriophage

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Abstract
.[long dash]18 races of phage active against 4 strains of Coryne-bacterium diphtheriae were obtained from: (a) intestinal contents of typical diphtheria cases, (b) intestinal contents and peritoneal washings of guinea pigs injected with C. diphtheriae, and (c) from cultures held at room temp. for 4-6 wks. Variations from typical rod to coccoid form, when grown on veal-peptone broth, are discussed. 3 partially susceptible strains, one of which was the P.W. No. 8 strain, and a 4th completely susceptible strain were isolated. This completely susceptible strain was obtained by isolation of a single coccoid cell from a diphtheria throat culture. It was shown that the coccoid form is the one stage specifically susceptible to phage. It is not unlikely, therefore, that every strain of C. diphtheriae, at some stage in its development passes through a susceptible form, since it has been recognized that phage multiplies only in presence of living, actively-reproducing, susceptible bacterial cells.