Ultrastructure of Vi phages I to VII of Salmonella typhi

Vi phages I to VII belong to three morphological groups. All phage heads are octahedral. The tail of phage I is long and contractile, whereas that of phage II is long and sheathless. Phages III, V, VI, and VII have very short tails and are nearly identical in morphology and dimensions. Preparations of phage IV supplied by three typing centers contain two distinct phages resembling either phage I or III. It seems necessary to study the morphology of typing phages for control purposes.