Temperature-dependent Variation in the Vi-typing Reactions of Strains of Salmonella typhi

Abstract

IT has been found that the specific Vi-phage sensitivity patterns of several of the types belonging to the Vi-phage typing scheme¹ are easily modified by changing the temperature of incubation of the typing plates. The types so far found to display this phenomenon are: D1, D4, D7, D8, D9 and D10. In general, each type exhibits its maximum specificity at 38.5° C (the standard temperature for Vi-phage typing). As the temperature is lowered, this specificity is progressively reduced. The diminution in the specificity of a given type is shown by a broadening of the sensitivity spectrum of the strain to the Vi-typing phages. This broadening is maximal at 36.5° C. All the types concerned are known to be lysogenic, and their structural formulæ² and sensitivities to a range of typing phages at 36.5° C and 38.5° C are shown in Table 1.