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Abstract
SUMMARY: A large collection of Staphylococcus aureus strains of human origin was examined for ability to inhibit the growth of Corynebacterium diphtheriae on the surface of solid media. Inhibition with the formation of a sharply-defined zone was produced by members of S. aureus Type 71, by certain closely-related strains, and by very few others. A small number of strains gave a wider hazy zone of inhibition. Both types of zone were produced by agents which diffused through agar, but not through cellophan, and killed C. diphtheriae. The two sorts of agent differed in their spectrum of activity for other corynebacteria. Strains of S. aureus which produced sharp zones of inhibition of C. diphtheriae also had a weak inhibitory activity against strains of S. aureus which were non-inhibitors or producers of hazy zones, but not on others which produced sharp zones. Ability to give rise to hazy zones persisted indefinitely in culture, but ability to produce sharp zones was regularly lost in culture after a few months. Loss of activity was accompanied by a widening of the susceptibility of the staphylococci to lysis by typing phages.
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