Alteration of Pasteurella pestis Bacteriophage Following Successive Transfer on Pasteurella pseudotuberculosis and on Shigellae

Summary Bacteriophage, originally recovered as a lytic agent for P. pestis, also lysed 31 of 40 strains of P. pseudotuberculosis. After adaptation to one of these (Spokane strain), it also lysed the remaining nine strains. When the adapted phage was transferred on S. dysenteriae, it reverted to its original activity; i.e., it again failed to lyse the nine strains of P. pseudotuberculosis which resisted the original phage. Activity for all strains was restored by transferring it on the Spokane strain. Lysates of S. dysenteriae, mixed with the adapted phage, caused no reversion to the original selective activity for only 31 strains of P. pseudotuberculosis. Transfers of the adapted phage on S. para-dysenteriae, S. sonnei, S. ambigua, or on all of these species in succession, did not alter its ability to lyse all strains of P. pseudotuberculosis. The size of plaques did not change during transfers on either the shigellae or the pasteurellae used.