SUMMARY: Phages capable of changing the production of the ‘Tween’-splitting enzyme by lysogenic conversion of strains were isolated from lysogenic strains within the phage type 52/52A/80/81 complex.

Phages isolated from TW strains were able to block the production of the ‘Tween’-splitting enzyme when they lysogenized TW strains. When the TW receptor strains were originally lysogenic, double lysogenization occurred. This change in the ‘Tween’ reaction was shown to be an example of lysogenic conversion. Phages isolated from TW strains were found able, in some instances, to change TW strains to TW strains on lysogenization. This change in reaction was found to be due to loss of the converting phage carried by the recipient strains by prophage substitution. Where prophage substitution did not occur and the strains became doubly lysogenic, the strains remained TW.

In these experiments a change of the typing pattern was found after lysogenization. The phage type of the lysogenized strain became similar to that of the donor strain. Non-typable strains were found, doubly lysogenic for phages which between them blocked all the reactions to the typing phages employed. The significance of these findings is discussed, especially the use of lysogenized strains in experiments designed to investigate the role of ‘Tween’ negavity as a virulence factor.


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