GENETICALLY STABLE TEMPERATURE-SENSITIVE MUTANTS OF SALMONELLA-TYPHI INDUCE PROTECTION IN MICE

Temperature-sensitive (ts) mutants of Salmonella typhi were isolated f ollowing treatment with nitrosoguanidine, and characterized with respe ct to cut-off temperature, ts phenotype and reversion frequency. Linka ge of the ts mutations to selectable chromosomal markers was establish ed by generalized transduction with bacteriophage phage Vi I, and the appropriate antibiotic resistances were transduced into the ts mutants . Multiple mutant S. typhi were then constructed by combining three in dependent ts mutations in one strain, utilizing linkage of three of th e mutations to erythromycin-, streptomycin- and methylglyoxal-resistan ce. Several recombinants are genetically stable, with calculated rever sion rates of less than 10(-22), and induce both protection from intra peritoneal challenge with the virulent parental wild-type S. typhi in mice and the formation of antibodies to the somatic O-9 and O-12, the flagellar H and the capsular Vi antigens.