Oral Immunization in Experimental Salmonellosis II. Characteristics of the Immune Response to Temperature-Sensitive Mutants Given by Oral and Parenteral Routes

Oral Immunization in Experimental Salmonellosis III. Behavior of Virulent and Temperature-Sensitive Mutant Strains in the Intestinal Tissues of Rats

Infection of rats via a Peyer's patch has been used as a means of studying the behavior of Salmonella enteritidis in intestinal tissues. The course of infection in the Peyer's patch and draining mesenteric lymph node is characterized by multiplication of the organism over a period of 4 days followed by a gradual decline in numbers; the organism also passes to the liver and spleen and may be isolated from these organs as well as the intestinal tissues for at least 4 weeks. Temperature-sensitive mutants derived from the virulent strain are unable to multiply and do not pass to the liver and spleen; they remain viable for periods of less than 2 weeks. A quantitative technique based on the number of viable organisms remaining in the injected Peyer's patch 48 hr after infection has been used to assess the immune state of rats. The results have clearly demonstrated that Salmonella immunity can only be induced by living vaccines and that although viable organisms remain in the reticuloendothelial tissues, organisms given in a challenge infection are immediately subject to enhanced bactericidal activity within the intestinal tissues. Under the conditions used here, humoral antibody does not seem to offer any protective effect against Salmonella infection in the intestinal lymphoid tissues.

Differential persistence, immunogenicity and protective capacity of temperature-sensitive mutants of Salmonella enteritidis after oral or intragastric administration to mice

The persistence of Salmonella enteritidis temperature-sensitive (ts) mutants of different phenotypes in Peyer's patches (PP) and the spleen, and their immunogenicity after intragastric (i.g.) and peroral (p.o.) administration to mice was investigated. After p.o. administration the ts mutant C/2/2 colonized PP, but was not recovered from the spleen. After i.g. administration the ts mutant E/1/3 colonized both the spleen and PP for at least 2 weeks. Mutant C/2/2 persisted in PP up to 8 days but was not found in the spleen. Mutant H/2/26, although it poorly colonized the PP, was recovered from the spleen up to day 15 after i.g. administration. Immunization with E/1/3 by either the i.g. or the p.o. routes protected mice from challenge with 100 LD50 of the virulent wild-type (wt) strain. Immunization with either C/2/2 or H/2/26 did not confer protection. The three ts mutants induced the production of local IgA after i.g. administration regardless of their protective capacity.

The adjuvant effect of a muramyl dipeptide (MDP) analog on temperature-sensitive Salmonella mutant vaccine

Adjuvant effect of a synthetic muramyl dipeptide analog, MDP-Lys (L18), MurNAc-L-Ala-D-glu[Lys(CO-(CH2)16-CH3)-OH]NH2 on a live Salmonella enteritidis vaccine, a temperature-sensitive mutant Ts-O strain that was obtained from the virulent S. enteritidis No.11 strain and could not grow at 37 degrees C, but could multiply at 25 degrees C as fast as the parent strain, was examined. Although the Ts-O organisms were avirulent and could hardly multiply in vivo when the organisms were injected into C57BL/6 mice and its mutant beige strain, which has a malfunction of phagocytic cells, injection of these mice with Ts-O endowed them with some protective immunity against infection by the virulent No.11 strain. When MDP-Lys(L18) was injected with Ts-O vaccine, the protection and the bactericidal capacity in the peritoneal cavities and spleens of these mice were augmented. MDP-Lys(L18) was still effective when it was injected at 48 h before or after the inoculation of Ts-O vaccine. Its effect was also observed against infection by the virulent S. cholerae-suis Hokkaido strain, a strain that does not share common O-antigenic determinants with the S. enteritidis No.11 or Ts-O strain. In addition, the mice that were inoculated simultaneously with Ts-O organisms and MDP-Lys(L18) were examined 10 days later for their footpad delayed type hypersensitivity reactions against Ts-O antigen. Mice inoculated with MDP-Lys(L18) and Ts-O showed augmented footpad swelling in comparison with the controls. These findings indicate that MDP-Lys(L18) is capable of augmenting the cellular immunity by live vaccine.

Temperature-sensitive growth mutants as live vaccines against experimental murine salmonellosis

Temperature-sensitive growth mutants of Salmonella enteritidis, NUB 209 and NUB 323, characterized as protein synthesis mutants, were unable to proliferate at 37 C and lost the parent's virulence. In mice, these mutants conferred high levels of protection as live vaccines. Although the vaccination effect of NUB 323 was not so good as that of NUB 209, NUB 323 was preferred as a safer live vaccine because this mutant was completely avirulent and no back mutation appeared.

Segmented filamentous bacteria in the rodent small intestine: Their colonization of growing animals and possible role in host resistance toSalmonella

The establishment and proliferation of a model population of autochthonous surface-associated microorganisms in the small bowel of growing rats (2-12 weeks of age) was studied. Segmented filamentous bacteria on the distal ileal villi were examined by scanning electron microscopy (SEM) and countedin situ by transect line analysis. In young animals, these bacteria first colonized the villous base, but occupied all areas on the villus by adult age. Their distribution on Peyer's patches was also noted.In growing animals, colonization of the ileal villi by filamentous bacteria was significantly correlated to the development of host resistance to fatal infection by orally-dosedSalmonella enteritidis. In animals givenSalmonella and examined by SEM and transmission EM (TEM), the pathogen was seen only on ileal tissue surfaces, predominantly the villous base, from which the autochthonous population was absent. Conversely, in animals with filamentous bacteria,Salmonella surface colonization was not observed. The results suggest a possible protective role for the surface flora in the small bowel.

The fate of temperature-sensitive salmonella mutants in vivo in naturally resistant and susceptible mice

The in vivo net growth rate of salmonellae in mice is faster with virulent than with attenuated strains, and slower in resistant than in susceptible mice, the latter difference being controlled by a single host gene (Ity). Mice were injected intravenously (i.v.) with nonreplicating temperature-sensitive (TS) salmonellae mutants: TS mutants from virulent parents survived better in the RES than those from attenuated or non-virulent parents as if the latter were more susceptible to bactericidal mechanisms. However, a TS mutant from a virulent parent (Salmonella typhimurium C5) did not consistently survive better in susceptible C5) did not consistently survive better in susceptible Itys than in resistant Ityr mice, suggesting that this gene may not operate by a bactericidal mechanism. In many animals the TS salmonellae caused septic arthritis which first appeared at 2--3 weeks. Subcutaneous inoculation in the tail caused local lesions and the organism spread to the RES, but did not cause arthritis in the short term.

Contribution to the study of live streptomycin-dependent Salmonella vaccines: the problem of reversion to a virulent form

The recovery of virulence by means of reversion of a live streptomycin-dependent (Sm D) Salmonella typhimurium vaccine was studied in CD-1 Swiss mice. Initially, a one-step Sm D mutant was obtained from a virulent streptomycin-sensitive (Sm S) S. typhimurium strain. Afterwards, two pools of streptomycin-independent (Sm I) revertants were prepared from the Sm D strain. The virulence of the Sm D strain and of the Sm I revertants was tested intraperitoneally. In the virulence testing the original suspension of the Sm I revertants, as well as their 1st and 10th passages on plain medium, medium+50 mug. streptomycin/ml. and medium+1000 mug. streptomycin/ml. were used. The results show that the Sm D mutant was avirulent, its avirulence being due to an intrinsic, genetic quality. The Sm I revertants, compared to the original Sm S strain, also displayed a lack of virulence. However, afterwards, the Sm I revertants behaved quite differently, according to their subsequent passages. Indeed, there was an increase in virulence after passages on plain medium, whereas similar passages on medium containing the drug, the virulence not only failed to increase, but disappeared almost completely. Moreover, the passages on medium containing 1000 mug. streptomycin/ml. induced a return to the status of drug-dependence. The danger of recovery of virulence by means of revertants is evaluated.

Comparative dynamics of salmonella infection after primary and secondary challenge of mice exposed to 10 and 23 C

Mortality of mice increased significantly as a result of cold exposure when the animals were challenged orally with Salmonella typhimurium, strain RIA. As reported earlier, cold exposure alone did not kill control animals nor did oral challenge at room temperature. No differences were apparent in the number of Salmonella per gram of liver-spleen, colon, or lung between groups of infected mice housed at 23 and 10 C. The number of bacteria increased equally in liver-spleen samples during the period of increasing mortality in the group housed at 10 C and the period of overt illness in those housed at 23 C. The ability to clear the bloodstream of a secondary intravenous challenge did not seem to be impaired by cold exposure. The bacterial load in the spleen and the rate of change in weight of that organ was equal in animals given a secondary challenge at 10 or 23 C. However, the absolute spleen weight was less in the cold-exposed group as was survival when the secondary challenge was administered 3 days after the primary oral challenge. The studies indicate that endotoxin from S. typhimurium may sensitize mice to the lethal effects of cold exposure. The increase in mortality observed in cold-exposed, infected mice is not due to greater bacterial proliferation in these animals. Rather, the combined stress effects of the bacterial agent(s) and cold may link lympholytic effects to impaired detoxification and increased energy demands, which often leads to lethal vascular collapse in cold-exposed, infected mice.

Comparative immunogenicity of heat-killed and living oral Salmonella vaccines

CD-1 mice were vaccinated intragastrically or intramuscularly with one or two doses of 200 mug of heat-killed Salmonella enteritidis 5694. Control mice were vaccinated with sublethal doses of living S. enteritidis Se795. The mice were challenged intragastrically with approximately 10(6)S. enteritidis 5694 SM(R) 7 to 14 days later, and the growth of the challenge population in the liver, spleen, mesenteric lymph nodes, lungs, and intestine was measured quantitatively. Mice receiving two doses of heat-killed vaccine by mouth were able to delay the systemic emergence of a gastrically introduced salmonella infection by 1 to 2 days. The corresponding liver and spleen populations were slightly lower than those seen in the normal controls. On the other hand, mice receiving the living, attenuated vaccine (either intravenously or intragastrically) developed an effective anti-salmonella immunity against subsequent reinfection.