Stimulation of gp91 phagocytic oxidase and reactive oxygen species in neutrophils by an avirulent Salmonella enterica serovar infantis strain protects gnotobiotic piglets from lethal challenge with serovar Typhimurium strain F98 without inducing intestinal pathology

Commensal Bacteria Impact on Intestinal Toll-like Receptor Signaling in Salmonella-Challenged Gnotobiotic Piglets

Gnotobiotic (GN) animals with simple and defined microbiota can help to elucidate host-pathogen interferences. Hysterectomy-derived germ-free (GF) minipigs were associated at 4 and 24 h post-hysterectomy with porcine commensal mucinolytic Bifidobacterium boum RP36 (RP36) strain or non-mucinolytic strain RP37 (RP37) or at 4 h post-hysterectomy with Lactobacillus amylovorus (LA). One-week-old GN minipigs were infected with Salmonella Typhimurium LT2 strain (LT2). We monitored histological changes in the ileum, mRNA expression of Toll-like receptors (TLRs) 2, 4, and 9 and their related molecules lipopolysaccharide-binding protein (LBP), coreceptors MD-2 and CD14, adaptor proteins MyD88 and TRIF, and receptor for advanced glycation end products (RAGE) in the ileum and colon. LT2 significantly induced expression of TLR2, TLR4, MyD88, LBP, MD-2, and CD14 in the ileum and TLR4, MyD88, TRIF, LBP, and CD14 in the colon. The LT2 infection also significantly increased plasmatic levels of inflammatory markers interleukin (IL)-6 and IL-12/23p40. The previous colonization with RP37 alleviated damage of the ileum caused by the Salmonella infection, and RP37 and LA downregulated plasmatic levels of IL-6. A defined oligo-microbiota composed of bacterial species with selected properties should probably be more effective in downregulating inflammatory response than single bacteria.

Oral vaccination with a rough attenuated mutant of S. Infantis increases post-wean weight gain and prevents clinical signs of salmonellosis in S. Typhimurium challenged pigs

We show that oral inoculation of 14 day old conventional piglets with a rough attenuated Salmonella enterica serovar Infantis 1326/28Ф(r) (serogroup C1), 24h prior to oral challenge with S. enterica serovar Typhimurium 4/74 (serogroup B), resulted in significant weight gain (~10%) measured at 14 days post-weaning (38 days of age). Two days after challenge the S. Typhimurium induced stunting and, in some cases loss, of villi but this was prevented by pre-inoculation with the S. Infantis strain. The clinical signs of disease associated with S. Typhimurium 4/74 challenge and faecal shedding were also significantly (P<0.05) reduced by pre-inoculation with the S. Infantis mutant. Pre-inoculation of pigs with the S. Infantis mutant also increased weight gain in pigs challenged with pathogenic Escherichia coli. However, Mycobacterium bovis BCG, an unrelated intracellular bacterium, did not protect against challenge with S. Typhimurium 4/74.

Emergency and therapeutic vaccination--is stimulating innate immunity an option?

There is increasing evidence that activation of innate immunity, in animals and man, by live vaccines, sub-unit vaccines or synthetic or non-synthetic stimulants can induce a profound and rapidly induced resistance to pathogens, including infectious agents that are unrelated to the stimulating antigen or agent. We review the evidence for this phenomenon and present the proposition that this approach might be used to stimulate immunity during the life of the animal when susceptibility to infection is high and when normal vaccination procedures may be inappropriate.

Epidemiology and interaction of Salmonella enterica serovar Derby, Infantis and Typhimurium with porcine alveolar macrophages

In this study we were interested in the serovars which are frequently isolated from pigs, i.e. S. Typhimurium, S. Derby and S. Infantis. First we collected different isolates of S. Infantis and S. Derby and compared them by macrorestriction analysis. In the second part of the study we infected porcine alveolar macrophages (PAMs) with representative strains of these serovars and S. Typhimurium and determined intracellular survival, cytotoxicity and cytokine response. In S. Derby, 17 different profiles in 51 isolates have been identified and in S. Infantis, 12 different profiles in 37 isolates have been identified. Four hours post-addition of bacteria to PAMs, higher numbers of intracellular S. Typhimurium than S. Derby or S. Infantis were observed. However, within next 24h, counts of S. Typhimurium did not change while S. Derby and S. Infantis increased their counts 10 and 5 times, respectively. The apparent inability of S. Typhimurium to multiply inside PAMs was caused by its higher cytotoxicity because PAMs infected with S. Typhimurium released LDH 24h post-infection to a significantly higher level than when infected with the other two serovars. The IL-1β, IL-8, IL-12p40, IL-23p19 and TNFα response to S. Derby and S. Infantis was always higher than to S. Typhimurium and the differences among the serovars were more significant at 4 than 24h post-infection. The lower cytokine signaling but higher cytotoxicity of S. Typhimurium for macrophages correlates with the higher virulence for pigs of this serotype when compared with S. Derby or S. Infantis.

Deletion of sodCI and spvBC in Salmonella enterica serovar Enteritidis reduced its virulence to the natural virulence of serovars Agona, Hadar and Infantis for mice but not for chickens early after infection

Salmonella enterica serovars Typhimurium, Enteritidis, Dublin, Choleraesuis or Gallinarum can colonise liver and spleen in particular hosts while infections with serovars Infantis, Agona, Hadar, etc. are usually limited to gastrointestinal tract. Reasons for this behavior are unknown, although it has been shown that sodCI and spv genes exhibit a strict distribution between more and less virulent serovars and they influence Salmonella virulence. However to what extent the presence or absence of these genes is associated with the increased virulence of serovars which possess them has never been addressed experimentally. In this study we therefore first confirmed the exclusive association of spvB and sodCI genes with the former group of serovars. In the next step we removed these two genes from S. Enteritidis genome and compared the virulence of such a mutant with the virulence of S. Infantis, S. Agona and S. Hadar for chickens and highly sensitive Balb/C mice. Single strain infection showed that the deletion of these two genes from S. Enteritidis resulted in the reduction of its virulence for mice but not for chickens. Mixed infection further confirmed these observations and indicated that in mice but not in chickens the virulence of sodCI and spv mutant was reduced to the natural virulence of serovars Infantis, Agona and Hadar. Although sodCI and spv genes do not influence S. Enteritidis virulence for chickens directly, they may be of an indirect effect through the increased persistence of S. Enteritidis in mice and increased probability of the reintroduction of S. Enteritidis into poultry flocks.

Non-typhoidal Salmonella infections in pigs: a closer look at epidemiology, pathogenesis and control

Contaminated pork is an important source of Salmonella infections in humans. The increasing multiple antimicrobial resistance associated with pork-related serotypes such as Salmonella Typhimurium and Salmonella Derby may become a serious human health hazard in the near future. Governments try to anticipate the issue of non-typhoidal Salmonella infections in pork by starting monitoring programmes and coordinating control measures worldwide. A thorough knowledge of how these serotypes interact with the porcine host should form the basis for the development and optimisation of these monitoring and control programmes. During recent years, many researchers have focussed on different aspects of the pathogenesis of non-typhoidal Salmonella infections in pigs. The present manuscript reviews the importance of pigs and pork as a source for salmonellosis in humans and discusses commonly accepted and recent insights in the pathogenesis of non-typhoidal Salmonella infections in pigs, with emphasis on Salmonella Typhimurium, and to relate this knowledge to possible control measures.

Cytokine response of porcine cell lines to Salmonella enterica serovar typhimurium and its hilA and ssrA mutants

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a facultative intracellular bacterium which can infect and colonize pigs. After contact with enterocytes and macrophages, S. Typhimurium induces production of cytokines thus triggering the innate immune response. In this study we evaluated the cytokine response of two porcine cell lines, IPI-2I and 3D4/31, of epithelial or macrophage origins, respectively, to the wild-type S. Typhimurium and its hilA and ssrA mutants. We observed that the 3D4/31 cell line essentially did not respond to S. Typhimurium infection when a medium with foetal calf serum was used. However when the 3D4 cell line was incubated overnight in the presence of porcine serum, it efficiently responded to the wild-type strain and the ssrA mutant but not to the noninvasive hilA mutant as measured by mRNA quantification of TNF-alpha, IL-8 and GM-CSF by the real-time RT-PCR. In IPI-2I, all the cytokines were also induced by the wild-type S. Typhimurium and the ssrA mutant although the induction of TNF-alpha was lower than that induced by the wild-type strain. The hilA mutant was unable to induce any of the cytokines tested. The ssrA mutant can therefore be considered as more suitable for further vaccine development as the stimulation of innate immune response is important for animal protection against a challenge with virulent strains.

Attenuated aroA Salmonella enterica serovar Typhimurium does not induce inflammatory response and early protection of gnotobiotic pigs against parental virulent LT2 strain

Cytokine and inflammatory response against virulent LT2 strain and its attenuated aroA deletion mutant of Salmonella enterica serovar Typhimurium were compared in gnotobiotic pigs. Contrary to the parental strain, the auxotrofic mutant did not induce IL-1beta, IL-18, TNF-alpha, and IFN-gamma in the ileum and plasma 24h after the infection, did not cause pathological changes in ileal epithelium and mesenteric lymph nodes or immunoreactivity of gp91 phox and peroxynitrite and was not immunostained for GroEL stress protein. The absence of induction of proinflammatory cytokines may be a reason why aroA mutant was unable to elicit any inflammatory response and protect pigs against challenge with virulent LT2 strain administered 24h later.