By the use of seven phage preparations, forty-one of fifty smooth strains of Salmonella thompson were classified into eleven types. The remaining nine strains were insusceptible to all the test phages; mouse passage did not render them susceptible. Acquired phage resistance was responsible for many of the strains being regarded as different phage types. A study of phage-resistant variants cast doubt on the complete validity of Bail's cross-resistance tests. The danger of using lysogenie cultures for the propagation of phages for the study of phage mutation were noted. Most of the S. thompson phages were fully active against strains of S. cholerae-suis but not for other Salmonella sp. that were tested.
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Williams SmithH.1948; Investigations in the typing of staphylococci by means of bacteriophage. I. The origin and nature of lysogenic strains. II. The significance of lysogenic strains in staphylococcal type designation. J. Hyg., Camb 46:74–82