Characterization and Grouping of Phage Types of Salmonella Paratyphi B, Especially of a New Type ‘Sittard’, by Sensitivity to Type Phages and by Lysogenic Properties

1. If lysogenicity is used in conjunction with sensitivity to a set of phages aa a tool for phage-typing, a further subdivision of the phage types of Salm. paratyphi B becomes possible, and also the types fall into a number of natural groups. When lysogenicity is tested by growth of two types in mixed culture, phages are produced which by their characteristic host ranges reveal a subdivision of types, parallel and complementary to the subdivision found by a study of lysogenicity. These phage reactions therefore possess a biological significance not entirely empirical. 2. The method of Craigie & Yen, which made possible a great advance in phage typing of Salm. typhi by means of preparations derived by adaptation from a single phage, has not yet been shown to be applicable to the typing of Salm. paratyphi B (Felix & Callow, 1951). As some of the typing phages used in the Felix & Callow system are identical with certain ‘natural’ phages derived from lysogenic strains, the lysogenic character of the types they reveal may be used in conjunction with these sensitivity tests as characteristics of phage types, if the set of phages is increased by addition of a few, shown in Table 1. This suggestion was made to the International Committee for Enteric Phage Typing in 1952. 3. In addition to the demonstration by the direct method of phages carried by lysogenic strains of Salm. paratyphi B, phages derived from mixed cultures of different types are characteristic of some phage types. Further development of the use of such phages and study of their nature and origin demand further research. Until further investigations have been made, the subdivision of phage types which they reveal must be regarded as tentative. 4. Strains from a large outbreak of paratyphoid fever, which could not be typed reliably by the method of Felix & Callow, possessed peculiar lysogenic properties which, together with certain phage reactions, justify their designation as a new type, ‘Sittard’. These strains can be identified if phages derived from tests of lysogenic power are used in addition to those of the Felix & Callow system. A number of strains from other sources, diagnosed as type ‘Sittard’ by their sensitivity to phages, were shown to possess lysogenic properties characteristic of the type. 5. A few other strains, shown in a similar way to represent new types, are described.