Non-lysogenic, non-toxinogenic Group A streptococci when infected by temperate bacteriophages isolated from known scarlatinal toxin-producing strains acquire the capacity to form erythrogenic toxin. This toxin causes a characteristic erythematous reaction in the skin of rabbits and is readily neutralizable by standard scarlatinal antitoxins.

The production of toxin appears to be related to the synthesis of mature phage particles since ultraviolet enhancement of phage production results in a concomitant increase in toxin titer. In contrast, there is no increase in the production of another extracellular product, deoxyribonuclease, by these lysogenized streptococci. Furthermore, cellular disruption studies indicate that the toxin probably does not exist in a preformed state within the cell.

Double diffusion reactions in agar indicate that a newly formed protein appears in the lysogenic culture filtrate and is absent in the non-lysogenic filtrates.

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