Vi-negative strains of Salmonella typhosa: attempts to induce W-V reversion and the use of non-Vi strains in evaluating typhoid vaccines.

Tully, Joseph G. (Walter Reed Army Institute of Research, Washington, D.C.) and Julius A. Currie. Vi-negative strains of Salmonella typhosa: attempts to induce W-V reversion and the use of non-Vi strains in evaluating typhoid vaccines. J. Bacteriol. 84:747-753. 1962.-Repeated attempts have been made to detect reversion of several W-form Salmonella typhosa strains to Vi antigen-containing cultures. Passage of the O-901, H-901, and Ty2W cultures through various mouse strains did not result in the recovery of V-form typhoid bacilli. Rabbits immunized repeatedly with non-Vi strains of typhoid bacilli, or with W cultures successively passed through mice, did not respond with Vi antibody formation. Attempts also were made to detect reversion of non-Vi strains passed in broth and plate cultures to which heat-killed Vi antigen-containing strains had been added. No evidence was obtained that the selection of Vi-containing cultures had been enhanced. The non-Vi typhoid strains employed in this study thus appeared to be stable W-form cultures. Viable-cell vaccines and acetone-killed and dried (AKD) vaccines of V- and W-form S. typhosa were compared in active mouse protection tests against intraperitoneal and intracerebral challenges with V- and W-form typhoid strains. Only Vi-containing cultures effectively protected mice against virulent V-form challenges, regardless of the route utilized. Greater quantities of both viable-cell and AKD vaccines prepared from non-Vi strains were required for protection against V- as well as W-form S. typhosa challenges.