The behaviour of a mutant strain of Salmonella typhimurium in experimental mouse typhoid

MUTATIONS TO PENICILLIN RESISTANCE IN THE ENTEROBACTERIACEAE THAT AFFECT SENSITIVITY TO SERUM AND VIRULENCE FOR THE MOUSE

Roantree, Robert J. (Stanford University School of Medicine, Stanford, Calif.), and John P. Steward. Mutations to penicillin resistance in the Enterobacteriaceae that affect sensitivity to serum and virulence for the mouse. J. Bacteriol 89:630-639. 1965.-Series of mutants resistant to benzylpenicillin or alpha-aminobenzylpenicillin were derived from serum-resistant strains of Escherichia coli and Salmonella by the gradientplate technique. Serum-sensitive mutants were detected in series derived from 16 of the 19 strains used, and these retained the parental O type. Most series were characterized by a mutational step to a high degree of sensitivity to serum. Penicillin-resistant mutants of virulent S. typhimurium and S. enteritidis were less virulent than the parent strains; those which were very sensitive to serum usually showed the greatest loss of virulence. One class of mutants from S. enteritidis was sensitive to human serum but virulent for mice. We found that the mice lack bactericidal antibody against this strain and that immunization with it leads to a high degree of protection.

The role of IFN-gamma in murine Salmonella typhimurium infection

Influence of both recombinant interferon gamma (r-IFN-gamma) and monoclonal anti-IFN-gamma on murine Salmonella typhimurium infection was studied in vivo. As a challenge we used either a virulent or an avirulent strain of S. typhimurium. The avirulent strain is unable to replicate in the mouse spleen. The effect of IFN-gamma or anti-IFN-gamma treatment on infection was assayed by counting the number of bacteria in the spleens 1, 2, 4 or 7 days after infection. Exogenously supplied IFN-gamma was found to decrease the number of both the virulent and the avirulent bacteria in the spleens 1 day after challenge but thereafter had no detectable effect. Anti-IFN-gamma-treated mice were unable to clear a sub-lethal dose of the virulent bacteria. The enhanced growth of the bacteria in the spleen was seen after 2 days of infection. In the spleens of anti-IFN-gamma-treated mice and control mice the fate of the non-replicating bacteria was similar. We conclude that the mice produce IFN-gamma during the early phase of Salmonella infection and that this causes a reduction in the apparent growth rate of the virulent bacteria. Because the avirulent bacteria, which do not multiply, were not affected by anti-IFN-gamma treatment, the effect of IFN-gamma is primarily bacteriostatic rather than bactericidal. After challenge, the production of IFN-gamma seems to start with a lag of approximately 2 days.

Protective immunity in mouse salmonellosis: comparison of smooth and rough live and killed vaccines

Protective immunity against Salmonella infection was studied in a mouse model. To study specificity of protection we used smooth (O-4,5,12) and rough vaccines; live and killed vaccines of both types were compared. The protection was assessed by enumerating the number of bacteria in the livers, and by following survival of the mice after intravenous challenge with smooth O-4,5,12 bacteria. Passively transferred antibodies induced by the smooth vaccines had a small protective effect and those induced by the rough vaccines no protective effect in this model. Both live vaccines induced long-lasting protective immunity which was much stronger than that mediated by antibodies. Since the live rough vaccine induced protective immunity and contained no O antigen we conclude that the protective immunity induced by it was mainly cell-mediated and directed to other antigens than the O antigen, the target of protective antibodies. Both killed vaccines also induced protective immunity, but this was weaker than that induced by the corresponding live vaccine.

Salmonella typhimurium virulence genes necessary to exploit the Itys/s genotype of the mouse

The studies described in this paper provide evidence that the pathogenesis of Salmonella typhimurium in mice is dependent on interactions between particular genotypes of the infected mice and the infecting Salmonella strain. This conclusion was based on data obtained by infecting a panel of BXD recombinant inbred mice with each of three S. typhimurium strains. One of the S. typhimurium strains was a transconjugant (WB500) produced in an interrupted mating between the two other strains, one (SR-11) of high and the other (LT2-Z) of low virulence for BALB/c mice. We found that strain WB500 appeared to have inherited from SR-11 a gene (or genes) which was required to exploit the Itys/s genotype in mice. However, WB500 apparently lacked other SR-11 virulence gene(s), whose effect on the in vivo growth of SR-11 was independent of the Ity genotype of the mouse.

Salmonellosis in orally infected specific pathogen-free C57B1 mice

Specific pathogen-free C57B1 mice are 100 to 1,000 times as sensitive as CD-1 mice to intravenous or oral challenge by Salmonella enteritidis or S. gallinarum. Resistance to infection by S. pullorum was unaffected. Growth of Listeria monocytogenes and Mycobacterium bovis (BCG) in intravenously infected C57B1 mice was similar to that seen in CD-1 mice. Quantitative counts of viable S. enteritidis in the walls of the stomach, small intestine, cecum, and large intestine and in the corresponding intestinal contents showed that most of the oral challenge inoculum was rapidly inactivated so that, by 24 hr, less than 1% was still viable. Overnight starvation and pretreatment with bicarbonate solution increased the relative survival of the challenge approximately 10-fold. Despite the rapid and extensive inactivation of the oral inoculum within the normal intestine, significant numbers of salmonellae reached the liver and spleen by 48 hr, and this systemic infection was subsequently responsible for the death of a high proportion of the challenged animals.

Cell-mediated resistance induced with immunogenic preparations of Salmonella typhimurium

Peritoneal cells obtained from mice immunized 15 or 30 days previously with (i) 0.1 LD(50) of attenuated Salmonella typhimurium (RIA), (ii) 20 mug (dry weight) of heat-killed Salmonella (SR-11), (iii) 20 mug (dry weight) of immunogenic ribosomal subfractions, or (iv) 20 mug of ribonucleic acid (RNA) subfractions were passively transferred to normal unimmunized mice. The ability of the recipient animals to inhibit or retard the multiplication of virulent challenge S. typhimurium 5 days post-infection was determined by pathogen counts on the carcasses. Peritoneal cells from donors immunized with the RIA, ribosomal, or RNA preparations (i) conferred maximal resistance to challenge 10 to 15 days after cell transfer and demonstrable resistance throughout the 45-day assay period, (ii) conferred resistance to infection when 10(5), 10(3), or 10(2) peritoneal cells were injected subcutaneously but not with fewer than 10(5) cells administered intraperitoneally, and (iii) rendered recipients capable of acting as donors of peritoneal cells that conferred demonstrable resistance on normal recipients. Recipients of peritoneal cells obtained from donors immunized with heat-killed bacteria were unable to (i) significantly inhibit bacterial proliferation at 10 days post-transfer, (ii) resist infection by a challenge inoculum greater than 50 LD(50), and (iii) secondarily confer resistance on normal animals through the passive transfer of cells or serum.

Salmonella abony-Salmonella typhimurium recombinant nonvirulent for the mouse

A previous genetic investigation involving a mouse-nonvirulent Salmonella abony donor (high frequency of recombination) and a virulent S. typhimurium recipient indicated that two unlinked "low-virulence" loci determined nonvirulence. A nonvirulent recombinant was analyzed to determine the basis for its nonvirulence. The recombinant was smooth (like the parental strains) and prototrophic. The doubling time in mouse serum of the recombinant and the S. abony parent (both streptomycin-resistant) was longer than that of the wild-type streptomycin-sensitive ancestor of the S. typhimurium recipient. The virulent recipient also grew poorly in serum. However, the nonvirulence of the recombinant was probably not due to its inheritance of the streptomycin-resistance allele from the donor, because other recombinants were streptomycin-resistant but still virulent. Unlike the nonvirulent S. abony (but like the S. typhimurium), the recombinant was insusceptible to rapid intravenous clearance in normal mice. It therefore appears that neither of the "low-virulence" loci determine diminished virulence by enhancing phagocytosis. Clearance of the recombinant was enhanced by opsonization with immune serum. Counts of viable bacteria in the blood, liver, and spleen of normal mice after intravenous challenge showed that the recombinant, like the S. abony donor, failed to proliferate in the tissues, whereas the virulent S. typhimurium did so markedly. It is concluded that the nonproliferation of the recombinant was determined by one or both of the "low-virulence" loci from the nonvirulent S. abony donor.

Heat-labile antigens of Salmonella enteritidis. I. Extraction of antigens

Milne, Margaret (University of Adelaide, Adelaide, Australia), and F. M. Collins. Heat-labile antigens of Salmonella enteritidis. I. Extraction of antigens. J. Bacteriol. 92:543-548. 1966.-Salmonella enteritidis strains of high and low mouse virulence were grown in continuous culture. Cell walls were obtained from both strains by sonic disruption, and the washed walls were extracted at 4 C with sodium dodecyl sulfate or sodium deoxycholate. The extracts were eluted with a saline gradient from a diethylaminoethyl cellulose column, and the separated peaks were tested for precipitin activity against rabbit antisera prepared with heator ethyl alcohol-killed vaccines. The separated antigens reacted less intensely with the antiserum to heat-killed cells than they did to the antisera prepared against alcohol-killed vaccine. Little antigenic difference could be detected between the extracts prepared from the virulent and the avirulent organisms.

Significance of Salmonellae Isolated from Apparently Healthy Mice

Morello, Josephine A. (Boston University School of Medicine, Boston, Mass.), Teresa A. DiGenio, and Edgar E. Baker . Significance of salmonellae isolated from apparently healthy mice. J. Bacteriol. 89: 1460–1464. 1965.—Three species of Salmonella were isolated from three groups of apparently healthy laboratory mice. The host-parasite relationship of one of these, a mutant S. typhimurium (lacks I and i antigens), was studied to determine the significance of these pathogens. Mice were fed undiluted broth cultures, and the infection was followed by means of fecal and organ cultures and a hemolytic serological test. Tissue invasion occurred during the early stages of the disease, but, within 1 week, the organism usually was localized in the intestinal tract. After 1 month, most of the mice had eliminated the organism completely. Antibody response to this organism was generally variable. Conditions of stress, including heat, cold, and cortisone administration, did not precipitate more severe disease in infected animals. The infection was maintained for longer periods of time in animals housed in groups than in those in individual cages. The presence of such salmonellae in laboratory animals appears to be of limited significance.

Resistance to reinfection in experimental mouse typhoid

Mice surviving infection with a strain of Salm. typhimurium of reduced virulence developed a progressive resistance to reinfection with virulent strains.

The degree of resistance was greater than that of vaccinated mice, although the primary infection had not caused any significant degree of natural selection or higher serum titres of O antibody.

The previously infected animals responded to reinfection with a virulent strain of Salm. typhimurium by gradually restraining bacterial growth. Many of the survivors eradicated the reinfecting strain.

The possible reasons for the difference between vaccinated mice and survivors of previous infection have been discussed.

I am indebted to the Medical Research Council for the provision of a grant towards the expenses of this investigation and to Mr T. Norris and Miss Italia S. Alderton for technical assistance.