STUDIES ON THE VIRULENCE OF BACTERIOPHAGE-INFECTED STRAINS OF CORYNEBACTERIUM DIPHTHERIAE

Abstract

Virulent strains of C. diphtheriae were isolated from 4 of 5 avirulent cultures of C. diphtheriae when the 4 cultures were incubated with a specific bacteriophage filtrate by which they were readily lysed. No virulent strains could be isolated when these same cultures were incubated with a phage filtrate by which they were only partially lysed. The 5th avirulent culture was not susceptible to either phage and yielded no virulent strains when incubated with either phage filtrate. Virulence tests were conducted in several ways, correlation being complete throughout. Controls of cultures incubated with saline were negative in all instances when tested for virulence. The extracellular nature of the toxic factor produced by the newly isolated virulent strains was demonstrated by filtration through a Seitz EK filter pad. All toxic reactions of the strains newly rendered virulent were shown to be preventable by the admn. of diphtheria antitoxin. The virulent strains isolated from the avirulent culture lysates were found to be stable. Also they were found resistant to the phage that lysed the avirulent culture from which they originated. In addition, these virulent strains were shown to be lysogenic. A filtrate of a naturally virulent strain of C. diphtheriae was tested on the avirulent cultures in a manner identical with that of the phage filtrates, but no virulent strains were isolated. The hypothesis considered most likely to explain this phenomenon is the spontaneous development of toxigenic mutants with selection by phage lysis.