Immunity to enteric infection in mice

Invasive Non-Typhoidal Salmonella Lineage Biofilm Formation and Gallbladder Colonization Vary But Do Not Correlate Directly with Known Biofilm-Related Mutations

Non-typhoidal Salmonella (NTS) serovars have a broad host range and cause gastroenteritis in humans. However, invasive NTS (iNTS) bloodstream infections have increased in the last decade, causing 60,000 deaths annually. Human-specific typhoidal Salmonella colonizes and forms biofilms on gallstones, resulting in chronic, asymptomatic infection. iNTS lineages are undergoing genomic reduction and may have adapted to person-to-person transmission via mutations in virulence, bile resistance, and biofilm formation. As such, we sought to determine the capacity of iNTS lineages for biofilm formation and the development of chronic infections in the gallbladder in our mouse model. Of the lineages tested (L1, L2, L3 and UK), only L2 and UK were defective for the rough, dry and red (RDAR) morphotype, correlating with the known bcsG (cellulose) mutation but not with csgD (curli) gene mutations. Biofilm-forming ability was assessed in vitro, which revealed a biofilm formation hierarchy of L3 > ST19 > UK > L1 = L2, which did not correlate directly with either the bcsG or the csgD mutation. By confocal microscopy, biofilms of L2 and UK had significantly less curli and cellulose, while L1 biofilms had significantly lower cellulose. All iNTS strains were able to colonize the mouse gallbladder, liver, and spleen in a similar manner, while L3 had a significantly higher bacterial load in the gallbladder and increased lethality. While there was iNTS lineage variability in biofilm formation, gallbladder colonization, and virulence in a chronic mouse model, all tested lineages were capable of colonization despite possessing biofilm-related mutations. Thus, iNTS strains may be unrecognized chronic pathogens in endemic settings.

Infection cycle of Salmonella enterica serovar Enteritidis in latent carrier mice 1The work was carried out at the Microbial Biotechnology Laboratory of Universidade Estadual de Santa Cruz, Ilhéus, Bahia State, Brazil

This work reports the distribution of an oral dose of Salmonella enterica serovar Enteritidis (SE) in C57Bl/6-Bcgr mice, to study its pathogenesis in a latent carrier animal. Mice orally inoculated with a high dose of SE developed a latent infection characterized by the absence of clinical symptoms in which the cecum is functioning as a “strategic site” of SE proliferation, releasing bacteria into feces intermittently over the 4-week study. A sequence of disruptions occurred in the small intestine at 1 day postinculation (PI). The microvilli exhibited different degrees of degeneration, which were reversible as the cells became vacuolated. From 2 days PI, SE was detected in the mononuclear phagocytic system, and an exponential growth of the remaining bacteria in tissues was observed until 4 days PI. The production of interferon gamma from 3 days PI is restricting the SE growth, and a plateau phase was observed from 4 to 15 days PI. A recurrence of the bacterial growth in tissue occurred from 15 to 28 days PI, especially in the cecum. Increasing our knowledge about the host–pathogen interaction of adapted pathogens with the ability to develop latency is essential for the development of an efficient strategy for Salmonella control.

Mouse models to assess the efficacy of non-typhoidal Salmonella vaccines: revisiting the role of host innate susceptibility and routes of challenge

Non-typhoidal Salmonella enterica (NTS) serovars Typhimurium and Enteritidis are important causes of bacterial gastroenteritis in the USA and worldwide. In sub-Saharan Africa these two serovars are emerging as agents associated with lethal invasive disease (e.g., bacteremia, meningitis). The development of NTS vaccines, based on mucosally administered live attenuated strains and parenteral non-living antigens, could diminish the NTS disease burden globally. Mouse models of S. Typhimurium and S. Enteritidis invasive disease can accelerate the development of NTS vaccines. Live attenuated NTS vaccines elicit both cellular and humoral immunity in mice and their efficacy is well established. In contrast, non-living vaccines that primarily elicit humoral immunity have demonstrated variable efficacy. An analysis of the reported studies with non-living vaccines against S. Typhimurium and S. Enteritidis reveals that efficacy is influenced by two important independent variables: (1) the innate susceptibility to NTS infection that differs dramatically between commonly used mouse strains and (2) the virulence of the NTS strain used for challenge. Protection by non-living vaccines has generally been seen only in host-pathogen interactions where a sub-lethal infection results, such as challenging resistant mice with either highly virulent or weakly virulent strains or susceptible mice with weakly virulent strains. The immunologic basis of this discrepancy and the implications for human NTS vaccine development are reviewed herein.

Gastrointestinal tract distribution of Salmonella enteritidis in orally infected mice with a species-specific fluorescent quantitative polymerase chain reaction

AIM: To identify and understand the regular distribution pattern and primary penetration site for Salmonella enteritidis (S. enteritidis) in the gastrointestinal tract.

METHODS: Based on the species-specific DNA sequence of S. enteritidis from GenBank, a species-specific real-time, fluorescence-based quantitative polymerase chain reaction (FQ-PCR) was developed for the detection of S. enteritidis. We used this assay to detect genomic DNA of S. enteritidis in the gastrointestinal tract, including duodenum, jejunum, ileum, cecum, colon, rectum, esophagus and stomach, from mice after oral infection.

RESULTS: S. enteritidis was consistently detected in all segments of the gastrointestinal tract. The jejunum and ileum were positive at 8 h post inoculation, and the final organ to show a positive result was the stomach at 18 h post inoculation. The copy number of S. enteritidis DNA in each tissue reached a peak at 24-36 h post inoculation, with the jejunum, ileum and cecum containing high concentrations of S. enteritidis, whereas the duodenum, colon, rectum, stomach and esophagus had low concentrations. S. enteritidis began to decrease and vanished at 2 d post inoculation, but it was still present up to 5 d post inoculation in the jejunum, ileum and cecum, without causing apparent symptoms. By 5 d post inoculation, the cecum had significantly higher numbers of S. enteritidis than any of the other areas (P < 0.01), and this appeared to reflect its function as a repository for S. enteritidis.

CONCLUSION: The results provided significant data for clarifying the pathogenic mechanism of S. enteritidis in the gastrointestinal tract, and showed that the jejunum, ileum and cecum are the primary sites of invasion in normal mice after oral infection. This study will help to further understanding of the mechanisms of action of S. enteritidis.

Host immune response to Salmonella enterica serovar Typhimurium infection in mice derived from wild strains

Studies of mouse models of endotoxemia and sepsis with gram-negative bacteria have shown that the host response is genetically controlled. Mice infected with the gram-negative bacterium Salmonella enterica serovar Typhimurium exhibit marked genetic differences in disease manifestation, and the wild-derived strain Mus musculus molossinus MOLF/Ei is extremely susceptible to S. enterica serovar Typhimurium. The kinetics of bacterial proliferation within the liver and the spleen and histological examination of tissue sections have suggested that MOLF/Ei mice do not succumb to infection because of overwhelming bacterial growth in the reticuloendothelial organs or massive tissue necrosis, as observed in other Salmonella-susceptible strains. MOLF/Ei mice respond normally to lipopolysaccharide (LPS) in vivo and in vitro, as determined by the production of tumor necrosis factor alpha and spleen cell mitogenesis. However, they have a unique cytokine profile in response to infection compared to that observed for other Salmonella-susceptible mice. There was increased expression of mRNA of the interleukin-1 alpha (IL-1 alpha) and IL-1 beta genes as the infection in the spleens and livers of MOLF/Ei mice progressed. Despite the fact that MOLF/Ei mice have the ability to respond to LPS and the fact that there are significant increases in IL-1 alpha and IL-1 beta mRNA, Nos2 in the spleen is not upregulated and nitrite production by spleen cells is reduced. At the central level, the inflammatory response is characterized by strong upregulation of the inhibitory factor kappa B alpha and Toll-like receptor 2 genes, two genes known to be regulated by LPS and IL-1 in the brain. The high levels of IL-1 expression in the spleens and livers of MOLF/Ei mice may have important implications for the activation of peripheral and central innate immune mechanisms.

Ability ofEscherichia coliO157:H7 isolates to colonize the intestinal tract of conventional adult CD1 mice is transient

In an attempt to improve upon a current mouse model of intestinal colonization by Escherichia coli O157:H7 used in this laboratory for vaccine development, nine clinical isolates of the pathogen were screened for their ability to persist in the intestinal tract of conventional adult CD-1 mice. None of the test isolates of E. coli O157:H7 were capable of colonizing these mice for a period of more than two weeks. Most of the isolates appeared to be benign for the experimental host, but one isolate was lethal. This virulence correlated with the ability of the latter isolate to produce large quantities of Shiga-like toxin 2 in vitro.

Effect of interleukin 12 neutralization on host resistance and gamma interferon production in mouse typhoid

Innately resistant (Ityr) A/J mice infected with the virulent Salmonella typhimurium C5 strain suppress the early exponential bacterial growth in the reticuloendothelial system toward the end of the first week of infection, with spleen and liver bacterial counts reaching a plateau phase. In vivo administration of neutralizing anti-interleukin-12 (IL-12) antibodies did not affect early bacterial growth in the tissues (days 1 to 3) but impaired the establishment of the plateau, with higher spleen and liver counts by day 7 of the infection in anti-IL-12 treated mice than in untreated controls. Gamma interferon (IFN-gamma) was detectable in the sera and spleen homogenates of both control and anti-IL-12-treated mice on days 3 and 7 of the infection. Noticeably, IFN-gamma levels were significantly lower in anti-IL-12 treated mice than in control animals. Splenocytes from uninfected A/J mice released IFN-gamma in response to concanavalin A (ConA) or to S. typhimurium C5. In vitro IL-12 neutralization dramatically impaired the IFN-gamma response to S. typhimurium but not to ConA. Splenocytes harvested from infected anti-IL-12 treated mice on day 7 of the infection produced significantly lower amounts of IFN-gamma upon in vitro stimulation with ConA and with a Salmonella protein-rich extract than did cells from similarly infected untreated control animals. Spleen cells from infected mice showed lower proliferative (mitogenic) responses to ConA and to a Salmonella soluble extract than did cells from uninfected mice. In vivo anti-IL-12 treatment significantly restored the ability of splenocytes from infected mice to proliferate in response to the antigens and ConA. In vivo neutralization of IL-12n in innately susceptible BALB/c mice ((ItyS)) immunized with a live attenuated aromatic-dependent Salmonella vaccine reduced host resistance to virulent oral challenge with S. typhimurium C5. Thus, in primary Salmonella infections, IL-12 mediates the suppression of growth of virulent salmonellae in the reticuloendothelial system, positively modulates IFN-gamma production, and is involved in the immunosuppression which accompanies the acute stages of the disease. IL-12 also contributes to host resistance to virulent organisms in secondary infections.

Growth rate paradox of Salmonella typhimurium within host macrophages

The growth rate of Salmonella typhimurium U937 within host macrophages was estimated by two independent methods. The extent to which ribosomal protein L12 is acetylated to produce ribosomal protein L7 changes markedly with the growth rate. By this measure, the intracellular bacteria appeared to be growing rapidly. Measurements of viable bacteria, however, indicated that the bacteria were growing slowly. A solution of this apparent growth rate paradox was sought by treating U937 cells infected with S. typhimurium X3306 with ampicillin or chloramphenicol to help determine the number of bacteria that were actively growing and dividing in the intracellular condition. Use of these antibiotics showed that by 2 h after invasion, the intracellular bacteria consisted of at least two populations, one static and the other rapidly dividing. This finding implies that previously described changes in the gene expression of S. typhimurium are important for the survival and/or multiplication of the bacteria within the macrophage.

Analysis of proteins synthesized by Salmonella typhimurium during growth within a host macrophage

Salmonella typhimurium is a facultative intracellular pathogen, able both to invade and to survive within eukaryotic cells and to grow in various extracellular environments. To compare the bacterial responses to these disparate environments and to shed light on the nature of the intracellular environment, we have examined the pattern of protein synthesis by two-dimensional polyacrylamide gel electrophoresis. The levels of approximately 40 proteins were observed to increase during growth within macrophage-like U937 cells, while approximately 100 proteins exhibited levels that were repressed relative to those of an extracellular control culture. To aid in the interpretation of these results, the patterns of proteins made by S. typhimurium exposed to various environmental conditions in the laboratory were determined. The intracellular protein pattern was then compared with each of these benchmark protein patterns. This analysis revealed that, as expected, the intracellular environment appears to impose numerous stresses on the bacteria, but unexpectedly, the macrophage-induced response was not a simple sum of the individual stress responses displayed during extracellular growth.

Antibody response and protection against challenge in mice vaccinated intraperitoneally with a live aroA O4-O9 hybrid Salmonella dublin strain

An auxotrophic Salmonella dublin (O9,12) strain, SL5631, with a deletion affecting gene aroA, was made into a partial diploid expressing the rfb (O-antigen-repeat-unit-specifying) gene cluster of Salmonella typhimurium (O4,12). By use of O4- and O9-specific antisera in indirect immunofluorescence assays, the resulting hybrid SL7103 was shown to express both the O4- and O9-antigen epitopes in the same bacterium. Qualitative and quantitative sugar analyses by gas-liquid chromatography on peralditol acetates of phenol-water-extracted lipopolysaccharides showed that the S. dublin and S. typhimurium repeating units (estimated on the basis of their tyvelose and abequose contents, respectively) were present in approximately equimolar amounts. The SL7103 hybrid auxotroph was avirulent when given intraperitoneally to NMRI mice in a dose of 10(8) CFU and elicited a protective immunity against intraperitoneal challenge with either virulent S. dublin (50% lethal dose of ca. 1.5 x 10(4) CFU versus < 1 x 10(1) CFU in nonimmunized mice) or virulent S. typhimurium (50% lethal dose of ca. 1 x 10(5) versus < 1 x 10(1) CFU in nonimmunized mice). Compared with the protection elicited in homologous systems (S. dublin SL5631 against S. dublin and S. typhimurium SL1479 against S. typhimurium), the protective efficacy of the hybrid was reduced approximately 70-fold against S. dublin challenge and 100-fold against S. typhimurium challenge. Vaccination with S. typhimurium SL1479 conferred no protection against S. dublin challenge, and vaccination with S. dublin SL5631 conferred no protection against S. typhimurium challenge. The protection elicited by the hybrid strain SL7103 is supposed to be mainly a consequence of serum antibodies directed against the immunodominant O4 and O9 epitopes.

Antigen-presenting characteristics of peritoneal cells of Salmonella enteritidis 11RX-infected mice

Investigation of the possibility that infection with intracellular bacterial parasites such as Salmonellae may modulate the function of antigen-presenting cells (APC) revealed no major change in APC function of peritoneal cells (PC) harvested from the peritoneal cavity of mice 1-3 days after intraperitoneal immunization with S. enteritidis 11RX. Analysis of the phenotype of the Salmonella-primed T cells which responded when cultured with PC from either normal or infected mice and Salmonella-antigen showed that only L3T4+ T cells proliferated. This was also true when PC from normal and infected mice were compared for their ability to induce allogeneic responses; both L3T4+ and Lyt-2.2+ T cells were induced to proliferate, with the majority belonging to the class I restricted, Lyt-2.2+ phenotype. Significant levels of alloantigen-specific Lyt-2.2+ cytotoxic T-cell activity were also induced in both types of cultures. However, a minor population of adherent cells which inhibited Salmonella antigen-specific T-cell proliferation in vitro was detected in peritoneal cell suspensions harvested 3 days after intraperitoneal immunization with S. enteritidis 11RX. Further characterization of these peritoneal cells revealed that they also inhibited the induction of in vitro T-cell responses to alloantigens. It is likely that the cells mediating these inhibitory effects belonged to a macrophage-like subset.

Invasion by Salmonella typhimurium is affected by the direction of flagellar rotation

When grown aerobically, Salmonella typhimurium exhibits a low level of entry into tissue culture cells. We have isolated an S. typhimurium Tn10 mutant which, when grown under aerobic conditions, efficiently invades HEp-2 cells. Sequencing of S. typhimurium DNA adjacent to the site of the Tn10 element showed that the insertion disrupted transcription of the aspartate receptor gene, tar. Polar effects of the transposon on downstream genes also eliminated chemotaxis. Isogenic nonchemotactic (Che-), as well as nonmotile (Mot-) and nonflagellated (Fla-), S. typhimurium strains were examined for their ability to invade HEp-2 cells. "Smooth" swimming Che- mutants (cheA, cheW, cheR, and cheY) were found to possess increased invasiveness for cultured mammalian cells. In contrast, a "tumbly" cheB mutant and Mot- (flagellated) strain were found to have decreased levels of tissue culture invasiveness. A Fla- strain was found to be as invasive as the wild-type strain if centrifugation was used to facilitate contact with the monolayer surface. In addition, the observed hyperinvasiveness of the smooth swimming tar::Tn10 mutant was suppressed when the strain was paralyzed by the introduction of a mot or fla mutation. A murine infection model was used to demonstrate that the mutant invasive phenotypes were also observed in vivo. These data are most consistent with the idea that the rotation and physical orientation of flagella around the bacteria affect the ability of salmonellae to enter host cells.

Route-related variation in the immunogenicity of killed Salmonella enteritidis vaccine: role of antigen presenting cells

In order to assess the role of the route of immunization on the immunogenicity of killed Salmonella vaccine, mice were immunized with killed S. enteritidis by intraperitoneal (i.p.) and intradermal (i.d.) routes. Whereas the former was non-immunogenic, the i.d. immunization generated an excellent delayed-type hypersensitivity response; further, i.p. immunization could even suppress the subsequent i.d. immunization. Since the peritoneal macrophages (MO) are known to be particularly low in Ia or MHC-class II antigens, so essential for antigen presentation, the non-immunogenicity by i.p. route was thought to be due to their poor presentation efficiency. Poly I: poly C, an interferon inducer, is known to enhance the MHC-class II expression; hence effect of poly I: poly C treatment on the immunogenicity of the killed vaccine by i.p. route was tested and indeed the non-immunogenicity was corrected. Poor efficiency of presentation of S. enteritidis antigen by peritoneal cells and its improvement by prior poly I: poly C treatment was further confirmed by in vitro lymphocyte transformation test using primed T cells and peritoneal cells from normal and poly I: poly C treated mice. Poly I: poly C treatment also enhanced expression of Ia antigens on peritoneal cells.

Novel virulence properties of the Salmonella typhimurium virulence-associated plasmid: immune suppression and stimulation of splenomegaly

Mice infected subcutaneously with wild-type Salmonella typhimurium, SR11, developed a significant splenomegaly when compared with mice infected with an equal number of a plasmid-cured strain. Further, the bacterial load in the spleen at 14 days after infection, measured as colony-forming units per gram tissue, was significantly higher in mice infected with the parent strain than in mice infected with the plasmid-cured strain. These data confirm the previously reported plasmid-associated ability of Salmonella to multiply within the spleen. In addition, lymph node cells (LNC) from mice infected with the parent strain had a significantly reduced ability to proliferate in response to concanavalin A, a T-cell mitogen, and to heat-killed S. typhimurium cells when compared with LNC isolated from mice infected with the plasmid-cured strain. Finally, reintroduction of a functional Tn5-tagged 90-kb plasmid into a plasmid-free strain restored its capacity to cause a marked splenomegaly and to suppress lymph node cell proliferation in BALB/c mice. These data demonstrate that the 90-kb plasmid of highly virulent S. typhimurium strains mediates several novel pathogenic properties in infected mice: (1) enhancement of the ability of Salmonella to multiply within the spleen; (2) stimulation of a splenic inflammatory response as displayed by marked splenomegaly; and (3) a general suppression of lymphocyte responsiveness to both T-cell mitogens and specific Salmonella antigens.

Plasmid-associated virulence of Salmonella typhimurium

We investigated the role of the 100-kilobase (kb) plasmid of Salmonella typhimurium in the virulence of this organism for mice. Three strains, LT2-Z, SR-11, and SL1344, which possessed 100-kb plasmids with identical restriction enzyme digestion profiles, were cured of their respective 100-kb plasmids after Tnmini-tet was used to label plasmids. Curing wild-type virulent strains SR-11 and SL1344 raised peroral 50% lethal doses from 3 x 10(5) and 6 x 10(4) CFU, respectively, to greater than 10(8) CFU. Both wild-type strains had intraperitoneal 50% lethal doses of less than 50 CFU, whereas the intraperitoneal 50% lethal doses for cured SR-11 and SL1344 were less than 50 and 400 CFU, respectively. Reintroduction of the Tnmini-tet-labeled, 100-kb plasmid restored wild-type virulence. Invasion from Peyer's patches to mesenteric lymph nodes and spleens after peroral inoculation was the stage of pathogenesis most affected by curing S. typhimurium of the 100-kb plasmid. Wild-type S. typhimurium replicated in spleens of mice inoculated intravenously to a greater extent than did plasmid-cured derivatives. Wild-type and cured strains equally adhered to and invaded Henle-407, HEp-2, and CHO cells; furthermore, the presence of the 100-kb plasmid was not necessary for replication of S. typhimurium within CHO cells. The 100-kb plasmid had no effect on phagocytosis and killing of S. typhimurium by murine peritoneal macrophages in vitro and in vivo. Similarly, wild-type and plasmid-cured strains were resistant to killing by 90% normal human, rabbit, and guinea pig sera. All wild-type and plasmid-cured S. typhimurium strains possessed complete lipopolysaccharide, as determined by silver staining solubilized cells in sodium dodecyl sulfate-polyacrylamide gels. We have confirmed the role of the 100-kb plasmid of S. typhimurium in virulence, primarily in invasion to mesenteric lymph nodes and spleens after peroral inoculation of mice. Involvement of the 100-kb plasmid in infection of mesenteric lymph nodes and spleens suggests a role for the plasmid in the complex interaction of S. typhimurium with cells of the reticuloendothelial system.

Mechanisms of acquired resistance in mouse typhoid

A polyvalent radiovaccine of Salmonella was shown to induce protective immunity in mice. The results revealed that the immunized mice progressively eliminated the challenged organisms and no Salmonella could be isolated after a period of 21 days. In contrast, Salmonella grew in the control mice and reached levels of 10(8) to 10(9) cfu/spleen resulting in the death of animals. Sera from both control and the immune mice were found to lack bactericidal activity. It was further observed that the vaccine induced delayed type of hypersensitivity and that antibody production as measured by bacterial agglutination and passive hemagglutination were low in response to the vaccine. However, the phagocytic activity of the reticuloendothelial system was considerably enhanced by the immunization. The results of experiments with immunosuppressed mice suggested the role of thymus derived (T) lymphocytes in the protection.

Effect of streptomycin administration on colonization resistance to Salmonella typhimurium in mice

The addition of 5 mg of streptomycin sulfate per ml to the drinking water of Swiss white mice resulted in a 100,000-fold reduction in the 50% implantation dose of streptomycin-resistant Salmonella typhimurium for the animals. When streptomycin-treated and untreated mice were challenged orogastrically with 10(3) viable S. typhimurium organisms, 100% of the treated and none of the untreated mice excreted the pathogen in their feces. Similarly, translocation of S. typhimurium from the intestinal tract to the liver, spleen, and mesentery occurred in 10 of 10 treated mice but in none of the untreated mice 7 days after challenge with 10(3) CFU. Studies of colonization dynamics showed that S. typhimurium was present at high population levels in the intestines of streptomycin-treated mice and in detectable levels in the liver, spleen, and mesentery within 72 h after challenge with 10(3), 10(5), or 10(8) organisms. In untreated mice challenged with either 10(3) or 10(5) S. typhimurium organisms, the organisms were isolated from ileal and cecal tissues but not from ileal or cecal contents or from extraintestinal tissue 72 h after challenge. When untreated mice were challenged with 10(8) organisms, however, S. typhimurium was present in all organs and in intestinal contents. Streptomycin treatment, therefore, facilitated colonization and development of streptomycin-resistant S. typhimurium populations in intestines of mice and the subsequent translocation of the organisms from the intestinal tract to other tissues.

Adoptive transfer of murine host protection to salmonellosis with T-cell growth factor-dependent, Salmonella-specific T-cell lines

A spent medium antigen was prepared from the avirulent RIA strain of Salmonella typhimurium. Lymph node cells isolated from female BALB/c mice injected subcutaneously with the spent medium antigen exhibited antigen-specific proliferation. By using these cells and T-cell growth factor, continuous spent medium antigen-specific, Thy 1.2-sensitive lines were generated. These cells exhibited antigen-specific proliferation in vitro and were effective in inducing significant (P less than 0.01) host protection when adoptively transferred to naive syngeneic mice.

New knowledge on pathogenesis of bacterial enteric infections as applied to vaccine development

Images

Experimental Campylobacter jejuni infection of adult mice

HA-ICR adult mice were studied to develop an animal model for Campylobacter jejuni enteritis in humans. Fecal and ileal cultures made by selective and nonselective methods showed that C. jejuni and related organisms are not bowel commensals. Intragastric feeding of 10(8) CFU of three different strains of C. jejuni produced infection in 100% of the animals, and infection rates were dose dependent. Pretreatment with antibiotics or opiates was not necessary to induce infection. Fresh isolates and strains passed on artificial media yielded similar infection rates. Infected mice did not show signs of illness, but transient bacteremia within 10 min of oral infection was observed in nearly 100%. The small intestine was the principal target organ, with epithelial inflammation seen 48 h after infection. Control mice of four species had undetectable serum immunoglobulin G antibody specific for the infecting strain, but infected mice showed peak titers at 1 week with rapid decline. Immunoglobulin M titers rose minimally, and immunoglobulin A titers did not rise. Infected mice uniformly became chronic asymptomatic excretors, shedding 10(4) to 10(6) CFU/g of feces; a minority were biliary carriers. Intestine carriage was most pronounced in the stomach and proximal small intestine. Because this experimental infection led to bacteremia, transient pathological changes, and immunoglobulin G titer rises, this model may be useful for evaluating the effects of prophylactic and therapeutic interventions.

Immunity to Salmonella infection

The foregoing literature review and data presentation have been set forth in the hope of clarifying some complex and confusing issues in regard to Salmonella infection. From a practical point of view, the information presented has implications for the direction to take with regard to improving the current typhoid vaccine, as the presently used acetone-killed cell preparation has considerable toxicity. The issues are important from a theoretical standpoint, because they have bearing on the nature of the concepts researchers and clinicians carry as working hypothesis with regard to the mechanisms of immunity to Salmonella infection. An incomplete appreciation of the literature seems to have led many scientists to believe that only cellular immunity can protect a mouse, and by analogy a human, against Salmonella. The logical deduction from such a premise is that only live vaccines will be effective in humans againsT S. typhi. Such a conclusion would appear unfounded, as documented in this review, for killed vaccines have been shown to be highly effective in vaccinating many mouse strains, as well as humans, against enteric fever.

Fate of Pasteurella hemolytica in conventionally raised and germfree mice

When Pasteurella hemolytica was introduced into conventionally raised ICR mice by a variety of routes (intraperitoneal, aerogenic, and oral), the inoculum was rapidly eliminated, and none of the mice died. Even when the inoculum was injected intraperitoneally into sublethally irradiated (600 rads) mice, the organisms were eliminated rapidly unless suspended in 10% hog gastric mucin. When germfree ICR mice were orally infected with P. hemolytica, the infection established itself in the intestinal tract and spread to the mesenteric lymph nodes but did not progress beyond this point. Despite the inability of P. hemolytica to establish itself systemically, the organism multiplied freely in mouse blood and a homogenate of normal mouse lung in vitro. Normal mouse peritoneal macrophages could phagocytose P. hemolytica in vitro, although not as efficiently as the control Listeria monocytogenes suspensions. The addition of hyperimmune bovine serum (opsonin) to the P. hemolytica suspension increased phagocytosis but did not greatly affect the subsequent bactericidal activity of the macrophages in vitro. The reason for the lack of pathogenicity shown by P. hemolytica in normal mice remains enigmatic.

Antigenic modification: its relation to protective host resistance in murine salmonellosis

Both the physical state of the immunogen and the route of immunization were found to be extremely important in inducing effective host resistance against salmonellosis.

Cellular antimicrobial immunity

Acquired resistance to infectious disease may be expressed by a predominantly humoral or a cellular mechanism or, more frequently, by a combination of the two. The cellular interactions which are responsible for the induction of the immune response in the skin, lung, intestinal mucosa, genitourinary tract, conjunctiva, and peritoneal cavity are discussed and the role of living or dead vaccines in the induction of acquired resistance is outlined. The host response involves three different cell types: the phagocytic cell (polymorphs or macrophages), the thymus-dependent (T) lymphocyte, and the thymus-independent (B) lymphocyte-plasma cell line. The normal unstimulated phagocytic cell is capable of killing most nonpathogenic bacteria that gain entry to the tissues. However, the presence of opsonic antibodies and activated macrophages is required to eliminate the pathogenic intracellular parasites. Such immunological activation involves the presence of sensitized T-lymphocytes in the lesion. The cellular response is also characterized by the simultaneous development of a state of delayed-type hypersensitivity (DTH), along with the antimicrobial CMI response. A rising humoral response normally develops subsequently. Killed bacterial cells (except when incorporated into Freund's complete adjuvant) induce the humoral response without the CMI reaction so that such vaccines are not able to fully protect the host against the naturally acquired disease. With the development of cell fractionation methods as well as the identification of distinctive cell surface markers, suspensions of B- and T-cells and macrophages can now be prepared for use in increasingly sophisticated transfer and reconstitution studies. The role of the different cell types in the expression of humoral and cellular immunity has been determined, and the effect of various immunopotentiating and immunosuppressive regimens on the immune system as a whole has been evaluated quantitatively. These studies have led to an appreciation of the role played by suppressor B- and T-cells in the interplay of both humoral and cellular components of the host defense system during the development of immune tolerance, desensitization, anergy, autoimmunity, and the expression of an anamnestic immune response following reinfection.

Intestinal colonization and virulence of Salmonella in mice

Within 3 h after oral challenge of mice with Salmonella typhimurium, foci of infection developed in the Peyer's patches of the small intestine. The numbers of organisms in the cecum, although in excess of those found in the small intestine, were not firmly associated with the cecal wall but were present largely in the cecum's contents. The Peyer's patches at first were remarkably incapable of eliminating even small numbers of Salmonella, but at about 7 days after infection developed the ability to eliminate a less virulent strain of S. typhimurium. Selected strains of Salmonella of varied virulence, and hybrid Escherichia coli/Salmonella typhimurium with varied O-antigens, revealed that those of low virulence could multiply within the intestinal Peyer's patches at nearly the same rate as a virulent strain, and the ability to multiply within the Peyer's patches was not dependent upon O-antigen type or smooth lipopolysaccharide. The ability of these strains to adhere to intestinal mucosa in vitro did not reflect on their ability to colonize the Peyer's patches, although strains of high in vitro adhesive ability appeared in greater numbers initially after oral challenge. Anti-O serum, ineffective in reducing the in vitro adhesive ability of virulent S. typhimurium, when given with the oral challenge prevented Peyer's patch colonization but was unable to prevent the appearance of a systemic infection. Anti-H serum, although effective in vitro in preventing adherence, had no effect in vivo. These experiments suggest that adhesiveness is neither essential nor sufficient for the virulence of Salmonella and that the usual development of a systemic infection after colonization of the small intestinal Peyer's patches may be subverted by the presence of O-antibody.

Protective effects of a supernatant factor from Salmonella typhimurium on Salmonella typhimurium infection of inbred mice

A supernatant factor prepared from 48-h cultures of Salmonella typhimurium has been used to immunize mice against subsequent challenge with normally lethal doses of S. typhimurium. The mouse strains used, C57BL and BALB/c, were sensitive to S. typhimurium with 50% lethal doses of less than 50 organisms. Two doses of supernatant factor, given intraperitoneally 20 days apart, protected mice against a subcutaneous challenge dose 10 days later of 100 50% lethal doses of S. typhimurium, resulting in 50 to 80% survival. The viable counts were reduced initially in organs of immunized mice compared with controls, and the multiplication of bacteria was delayed, although the final levels found in the organs would normally have been lethal. Protection obtained was specific for S. typhimurium in that no increased survival was shown after Salmonella enteritidis challenge of immunized mice. Although lipopolysaccharide was demonstrated in the supernatant factor, lipopolysaccharide alone did not protect challenged mice. Supernatant factor produced delayed-type hypersensitivity reactions in mice sensitized with nonlethal doses of Salmonella. The nature of the active factor, found to be partially protein, has yet to be elucidated.

Studies on oral adjuvants against murine salmonellosis

1) Attempts were made to develop oral adjuvants against murine salmonellosis. 2) Streptomycin, levamisole and PHA show potential immunoenhancing properties against salmonella infection. 3) The mode of action of these agents remain to be elucidated. Observed results of PHA enhancement may be related to its blastogenic effects in the splenic T-cells. 4) Decrease in certain bacterial flora resulting in less antigenic competition may be the mode of action of streptomycin as adjuvant when added to oral salmonella vaccine.

A study of the efficacy of typhoid vaccine in inducing humoral and cell-mediated immune responses in human volunteers

The nature of protective immunity against typhoid fever in man is not at present well understood. Work on animal models and earlier studies from this laboratory indicate an important protective role for cellular immunity. The present work attempts to study the efficacy of the conventional typhoid vaccine in inducing specific cellular and humoral immune responses. The study on fifty-eight new army recruits and thirty-one civilian volunteers showed adequate humoral responses after vaccination. However, vaccination failed to induce a significant cellular immune response. In addition, a transient suppression of cellular immunity was observed in the immediate post-vaccination period in ten subjects who possessed natural cellular immunity before vaccination. These findings indicate the need for improving the typhoid vaccine so that it will induce cellular immunity as well as a humoral response. It also points to the necessity for obtaining detailed knowledge of the post-vaccination anergy as it could be important in timing public health programmes.

Immunological study of typhoid: immunoglobulins, C3, antibodies, and leukocyte migration inhibition in patients with typhoid fever and TAB-vaccinated individuals

The development of humoral and cell-mediated immune responses to Salmonella typhi antigens and immunoglobulin and C(3) levels were determined in patients suffering from typhoid fever, TAB-vaccinated individuals, and appropriate controls. In 45 patients with typhoid, a significant elevation of immunoglobulin M (IgM) level was noted from the first week of illness onwards. Eighteen TAB-vaccinated persons also showed a significant elevation of IgM levels. In typhoid sera, the anti-O and anti-H antibodies were mostly 2-mercaptoethanol (2-ME) sensitive. The rise of IgM level correlated well with the 2-ME-sensitive anti-O and anti-H antibodies seen in typhoid patients. The anti-O antibodies in the TAB-vaccinated group were almost entirely 2-ME sensitive, but both 2-ME-sensitive and -resistant anti-H antibodies were detected in the TAB group. A marked increas in C(3) level was also noted in patients with typhoid. The cell-mediated immunity (CMI), as measured by leukocyte migration inhibition tests, was demonstrable in 15 of 22 patients with typhoid. On the other hand, only 8 of the 20 normal subjects, 5 of the 16 fever control cases, and 6 of the 18 TAB-vaccinated individuals gave a positive CMI. The latter three groups were comparable with each other but were significantly different from the typhoid patients. It was concluded that TAB-vaccination did not induce CMI even though it induced the development of antibodies, the latter being comparable with those of the patients with typhoid. The significance of these findings is discussed.

Growth of typhoid and paratyphoid bacilli in intravenously infected mice

The in vivo growth of Salmonella paratyphi A, S. paratyphi B, S. paratyphi C, and S. typhi, as well as of an S. typhi-typhimurium hybrid, was studied in three different strains of mice. S. paratyphi A and B and S. typhi demonstrated very little growth potential in any of the intravenously infected mice, even after as many as 20 serial mouse passages. It was noted, however, that small numbers of viable S. paratyphi B and S. typhi persisted in the spleens of infected mice for up to 28 days. Salmonella paratyphi C and the S. typhi-typhimurium hybrid gave rise to progressive systemic infections beginning from very small intravenous inocula. The median lethal doses for the C57B1 strain of mouse were about five organisms. The relevance of these findings with regard to the development of an animal model for studying human typhoid fever vaccines is discussed.

The route of enteric infection in normal mice

This study followed the early pathogenesis of orally induced murine typhoid fever. Intragastrically administered Salmonella enteritidis moves quickly through the normal undisturbed gut so that only a small residuum remains in the cecum and large intestine after the first few hours. Dye injection of the gut wall was used to show that lymph from discrete portions of the gastrointestinal tract drains to separate lymph nodes, probably via the regional Peyer's patches. Plating techniques capable of detecting a single colony-forming unit of S. enteritidis within the different Peyer's patches and draining lymph nodes indicate that, although the cecum and large intestine are exposed to large numbers of Salmonella for longer time periods than the small intestine, the primary site of bacterial penetration involves the distal ileum. This area of the small intestine as well as the cecum are both drained by the distal mesenteric lymph nodes, and were the only nodes which contained detectable numbers of viable Salmonella over the first 24 h of infection. Neither the pyloric nor the proximal mesenteric lymph nodes (which drain the stomach and duodenum) nor the pancreatic and caudal lymph nodes (which drain the transverse and descending colon) contained viable Salmonella. Salmonella were observed to infect the ileal mucosa and its Peyer's patches. With time, this infection progresses to the draining lymph node and ultimately reaches the liver and spleen. Some of the implications of these findings relative to the development of acquired resistance to enteric disease are discussed.

Experimental Yersinia enterocolitica infection in mice: kinetics of growth

Infection of several strains of laboratory mice with a virulent strain of Yersinia enterocolitica was followed by performing viable bacterial counts on homogenates of selected tissues at intervals after intragastric, aerogenic, or intravenous infection. It is observed that CD-1 mice are more susceptible to Y. enterocolitica infection than either the C(57)B1/6 or B6D2 strains. Development of an enteric infection is dose dependent; less than 5 x 10(7) organisms by mouth yields sporadic, low levels of systemic infection, with many of the animals showing no apparent infection. Increasing the challenge inoculum by a factor of 10 eliminates the variability among the animals, giving rise to an enteric infection in all of the mice that moves quickly to the mesenteric lymph node. The bacterial population in the lymph node multiplies rapidly, and the infection is disseminated to the spleen, liver, and lungs, ultimately killing most of the animals. Exposure to an aerogenic challenge of less than 1,000 organisms resulted in a fulminating pneumonitis with an invariably fatal outcome. Intravenous challenge with 500 organisms caused a rapidly fatal, systemic infection. The growth of the bacteria in the intravenously infected mouse depends upon the temperature at which the challenge inoculum had been grown in vitro. At temperatures below 26 C, the bacteria are cleared from the blood at a slower rate and are more resistant to intracellular killing, as compared to organisms grown at 37 C. This effect results in the inoculum increasing to greater numbers in the tissues in a shorter period of time.

Polyarthritis associated with Salmonella infection in rats

Rats infected intravenously with Salmonella enteritidis develop a chronic destructive polyarthritis. The joint lesions resemble those of human rheumatoid arthritis in distribution and pathology. On the basis of histological and microbiological studies, involvement does not appear to be the result of intra-articular sepsis. Instead, the data favor the view that transient infection incites an immunological response that localizes in the joint and becomes destructive.

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.

Oral immunization of mice with killed Salmonella typhimurium vaccine

A study was undertaken to assess the efficacy of oral, parenteral, and intraperitoneal immunization methods of administering killed Salmonella typhimurium vaccine to mice and to evaluate the effectiveness of single and multiple doses of the vaccine containing varied numbers of the killed bacteria. A further objective of this study was to evaluate the effect of adding substances to the vaccine to which have been ascribed "adjuvant" properties. The protection was estimated by isolation of bacteria from the spleen and feces after oral challenge of the mice with live S. typhimurium. The results showed that one or more doses of 10(10) organisms given orally led to significant protection. This rate of protection increased proportionately with the number of doses up to 10 doses, which offered 100% protection. Streptomycin, when added to multiple doses of 10(9) or more organisms given orally, increased the degree of protection, but beryllium sulfate and pertussis vaccine did not. Although multiple doses afforded similar systemic protection by all three routes of immunization, oral immunization yielded significantly greater local protection than that observed after subcutaneous or intraperitoneal immunization.

Immunity in experimental salmonellosis. 3. Comparative immunization with viable and heat-inactivated cells of Salmonella typhimurium

Vaccination with viable cells of an avirulent Salmonella typhimurium galE mutant provides mice with solid specific immunity against subsequent infection with a virulent smooth strain. Such a live vaccine is markedly more potent than one prepared from inactivated cells of the virulent smooth strain. The superiority of the live vaccine is particularly well demonstrated when the oral route of application is used. The protective capacity of the galE mutant is based on its ability to synthesize complete smooth-like cell wall lipopolysaccharide in vivo.

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.