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Infect Immun. 1973 January; 7(1): 5-8
Copyright © 1973 American Society for Microbiology. All Rights Reserved.

Assay of Typhoid Vaccines with Salmonella typhosa-Salmonella typhimurium Hybrids

Laboratory Centre for Disease Control, Ottawa, Ontario, Canada
Department for Bacterial Immunology, Division of Communicable Disease and Immunology, Walter Reed Army Institute of Research, Washington, D.C. 20012

ABSTRACT

Salmonella typhimurium hybrids expressing the S. typhosa antigens 9, d, and Vi were constructed by genetic crosses with an S. typhosa Hfr donor. The hybrids retained the same degree of mouse virulence as their S. typhimurium parent strain, the minimum lethal dose being less than 50 organisms when tested either in C₅₇ black mice or Swiss white mice. Vaccination of the Swiss white mice with S. typhosa Ty2 vaccines prepared by acetone treatment, alcohol treatment, or heat-killing conferred significant protection against challenge by the hybrid strains but not against their S. typhimurium parent. Both the acetone-treated and alcohol-treated typhoid vaccines were markedly more protective than the heat-killed, phenol-preserved vaccine.