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Purified Vi antigen, acetic anthydride-treated Salmonella typhosa endotoxin, and potassium methylate-treated S. typhosa endotoxin employed as vaccines in Swiss white mice failed to protect these animals against challenge with a virulent S. typhimurium hybrid expressing S. typhosa antigens.
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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 C(57) 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.
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Approximately half of Salmonella typhosa hybrids resulting from mating with Escherichia coli Hfr donors inherit the selected donor marker by recombination, and the length of the E. coli chromosomal segment most frequently incorporated in these recombinants is between 1 and 2 min.
Salmonella typhimurium mutants sensitive to coliphage P1 are resistant to salmonella phage P22 and lose their P1-sensitivity upon reversion to P22-sensitivity. A tryptophan-requiring Salmonella typhosa - Escherichia coli hybrid, which has the unique ability to serve as recipient in transduction mediated by both P22 and P1, was sued to determine if P22 and P1 adsorb at the same or overlapping sites: (i) The adsorption of each of P1 and P22 is similar when added individually or together to the hybrid at a saturating multiplicity of infection (moi). (ii) P1 grown on trp+ E. coli yields the maximum frequency of Trp+ abortive transductions at an moi of 6 with the trp hybrid recipient; the presence of increasing numbers of P22 grown on trp S. typhimurium does not decrease the number of Trp+ transduction from P1. (iii) A mixture of P1 (grown on trp+ E. coli) and P22 (grown on trp+ S. typhimurium) yields more abortive transductions than does P1 alone. Thus phages P1 and P22 adsorb to the hybrid cells on different sites.
The immune response to Salmonella typhosa during hyperimmunization of dogs and rabbits by intravenous administration, at three different dose levels, three times a week for about seven months, was analysed. The pattern of immune response to both 'H' and 'O' antigen was determined, and antibody activity associated with IgM and IgG was clearly distinguished. Higher levels of both IgM and IgG activity were produced in rabbits than in dogs. The usual pattern of the early onset of IgM synthesis, with subsequent termination of active synthesis while IgG antibody was being formed, was observed in both groups. These results showed that with sufficient stimulation, hyperimmune anti-'O' sera may demonstrate a predominant IgG activity rather than the IgM activity considered to be characteristic of the response to bacterial lipopolysaccharides. Quantitative comparison of the amount of antibody produced to 'O' antigen by the quantitative precipitin method showed that the major differences between the dog and the rabbit remain, with a poorer formation of IgG antibody in the dog. The differences observed between the two species reflect the functioning of an antibody mediated feedback system at a lower threshold in the dog than in the rabbit.
Johnson, E. M. (Walter Reed Army Institute of Research, Washington, D.C.), Stanley Falkow, and L. S. Baron. Recipient ability of Salmonella typhosa in genetic crosses with Escherichia coli. J. Bacteriol. 87:54-60. 1964.-Salmonella typhosa strain 643WS(r) was mated with Escherichia coli Hfr strains W1895 and Hayes, with single marker selection for the E. coli genes lac(+) (lactose utilization) and ara(+) (arabinose utilization). Four classes of Salmonella hybrids were obtained, each class possessing one marker derived from one E. coli parent. In a series of eight genetic crosses, in which each hybrid class was remated with each of the Hfr strains, recipient ability of the hybrids was increased only when their substituted E. coli genetic section matched the lead region of the Hfr chromosome. Data obtained from replica plating indicated that the S. typhosa 643WS(r) population is probably homogeneous with respect to its initial ability to mate with E. coli. Transfer of the F-lac element was found to occur only slightly less efficiently from an E. coli F' donor to S. typhosa than it did to an E. coli F(-) strain. This indicated that E. coli is able to conjugate almost as effectively with S. typhosa as it does intraspecifically. However, failure to detect beta-galactosidase production by merozygotes derived from an E. coli Hfr W1895 x S. typhosa mating indicated that transfer of chromosomal lac(+) may be impaired.
Changes in the fluorescence of the cell wall of Salmonella typhosa (TY2 W) were studied during growth after direct labeling with fluorescein conjugated homologous or "anti-O" globulins. Fluorescence decreased evenly with culture growth and cell division, but the addition ofchloramphenicol resulted in large, nondividing cells that showed increasing interruption of fluorescence of the wall marker. The process thus differs from the equatorial origin and discrete hemispherical addition of new wall previously described in Streptococcus pyogenes. These findings, in addition to demonstrating the formation of new wall in the presence of chloramphenicol, appear consistent only with the concept that wall replication in the salmonellas occurs by means of diffuse intercalation of new materials among old.