The Type A Phages of Salmonella typhimurium: Identification by a Standardized Cross-immunity Test

Abstract

Use has been made of an indicator strain (Salmonella typhimurium Q1), which contains no symbiotic phage, and is sensitive to all known phages of S. typhimurium. This strain, with the use of appropriate techniques can be symbiotically infected with these phages. It has thus been possible to prepare a series of lysogenic cultures, alike in all respects except in the prophage which they carry, and by using such strains to test cross-immunity with a high degree of accuracy. The immunity pattern of 598 type A phages has been examined, and subdivisions in the original types revealed. The test is described and the significance of the findings discussed.