Host adapted serotypes of <i>Salmonella enterica</i>

Salmonella constitutes a genus of zoonotic bacteria of worldwide economic and health importance. The current view of salmonella taxonomy assigns the members of this genus to two species: S. enterica and S. bongori. S. enterica itself is divided into six subspecies, enterica, salamae, arizonae, diarizonae, indica, and houtenae, also known as subspecies I, II, IIIa, IIIb, IV, and VI, respectively. Members of Salmonella enterica subspecies enterica are mainly associated with warm-blooded vertebrates and are usually transmitted by ingestion of food or water contaminated by infected faeces. The pathogenicity of most of the distinct serotypes remains undefined, and even within the most common serotypes, many questions remain to be answered regarding the interactions between the organism and the infected host. Salmonellosis manifests itself in three major forms: enteritis, septicaemia, and abortion, each of which may be present singly or in combination, depending on both the serotype and the host involved. Although currently over 2300 serovars of Salmonella are recognized, only about 50 serotypes are isolated in any significant numbers as human or animal pathogens and they all belong to subspecies enterica. Of these, most cause acute gastroenteritis characterized by a short incubation period and a severe systemic disease in man or animals, characterized by septicaemia, fever and/or abortion, and such serotypes are often associated with one or few host species. It is the intention of this review to present a summary of current knowledge of these host-adapted serotypes of S. enterica. The taxonomic relationships between the serotypes will be discussed together with a comparison of the pathology and pathogenesis of the disease that they cause in their natural host(s). Since much of our knowledge on salmonellosis is based on the results of work on Typhimurium, this serotype will often be used as the baseline in discussion. It is hoped that an appreciation of the differences that exist in the way these serotypes interact with the host will lead to a greater understanding of the complex host–parasite relationship that characterizes salmonella infections

Investigating age- and virulence factor- dependent innate immune activation during neonatal meningitis associated E. coli infection

Neonatal meningitis-associated Escherichia coli (NMEC) is a leading cause of early-onset sepsis and meningitis. While current antibiotic protocols have significantly reduced mortality associated with neonatal sepsis and meningitis, surviving infants are at a significantly increased risk of developing life-long neurologic impairment compared to healthy infants. This continued risk of lasting neurologic damage along with a recent rise in antibiotic resistant NMEC strains has precipitated a need for new therapeutic strategies. Targeted immune-based therapeutics may serve as desirable adjunct therapies; however, there are many challenges to their development. The neonatal immune system is immature compared to the immune system of adults, leading to an increased risk of infection. Here we assess the role of IL-1 secretion, which is known to be diminished in neonates, in the pathogenesis of a murine model of NMEC infection. We further highlight one potential mechanism for decreased IL-1 secretion during the neonatal period. To further complicate the development of immune-based therapeutics aimed at treating NMEC infection, NMEC strains can possess many different virulence factors with the potential to alter immune cell activation. While some of these factors, such as OmpA, have been well-characterized in the context of NMEC infection, many potential virulence factors have not. Here we show that the pore-forming toxin [alpha]-hemolysin activates purinergic receptors, leading to improved bacterial clearance and decreased mortality in a neonatal mouse model of NMEC infection. Together, the data presented here provides new insight into both neonatal immunity and the role of virulence factor-specific immune activation on the pathogenesis of NMEC infection, and may serve as a stepping stone for the development of not only new immune-based therapeutics, but also new diagnostic and prognostic tools for use during neonatal infection.Includes bibliographical references

Avian Pathogenic Escherichia coli (APEC) Strain-Dependent Immunomodulation of Respiratory Granulocytes and Mononuclear Phagocytes in CSF1R-Reporter Transgenic Chickens

Avian pathogenic Escherichia coli (APEC) cause severe respiratory and systemic disease in chickens, commonly termed colibacillosis. Early immune responses after initial infection are highly important for the outcome of the infection. In this study, the early interactions between GFP-expressing APEC strains of serotypes O1:K1:H7 and O2:K1:H5 and phagocytic cells in the lung of CSF1R-reporter transgenic chickens were investigated. CSF1R-reporter transgenic chickens express fluorescent protein under the control of elements of the CSF1R promoter and enhancer, such that cells of the myeloid lineage can be visualized in situ and sorted. Chickens were separately inoculated with APEC strains expressing GFP and culled 6 h post-infection. Flow cytometric analysis was performed to phenotype and sort the cells that harbored bacteria in the lung, and the response of the sorted cells was defined by transcriptomic analysis. Both APEC strains were mainly detected in CSF1R-transgeneneg (CSF1R-tgneg) and CSF1R-tglow MHC IIneg MRC1L-Bneg cells and low numbers of APEC were detected in CSF1R-tghigh MHC IIpos MRC1L-Bpos cells. Transcriptomic and flow cytometric analysis identified the APECpos CSF1R-tgneg and CSF1R-tglow cells as heterophils and the APECpos CSF1R-tghigh cells as macrophages and dendritic cells. Both APEC strains induced strong inflammatory responses, however in both CSF1R-tgneg/low and CSF1R-tghigh cells, many immune related pathways were repressed to a greater extent or less activated in birds inoculated with APEC O2-GFP compared to APEC O1-GFP inoculated birds. Comparison of the immune pathways revealed the aryl hydrocarbon receptor (AhR) pathway, IL17 and STAT3 signaling, heterophil recruitment pathways and the acute phase response, are modulated particularly post-APEC O2-GFP inoculation. In contrast to in vivo data, APEC O2-GFP was more invasive in CSF1R-tghigh cells in vitro than APEC O1-GFP and had higher survival rates for up to 6 h post-infection. Our data indicate significant differences in the responses induced by APEC strains of prevalent serotypes, with important implications for the design and interpretation of future studies. Moreover, we show that bacterial invasion and survival in phagocyte populations in vitro is not predictive of events in the chicken lung

Pathogenic mechanisms of Photobacterium damselae subspecies piscicida in hybrid striped bass

Photobacterium damselae subspecies piscicida, previously known as Pasteurella piscicida, is an important pathogen of hybrid striped bass and many fish species cultured in brackish water in the United States, Japan, Europe, and the Mediterranean. The purpose of this study is to investigate virulence mechanisms that contribute to the pathogenesis of this organism. The ability of P. damselae to survive/replicate within hybrid striped bass macrophages was evaluated with an in vitro killing assay. Results indicated that the numbers of bacteria recovered from macrophages at 3, 6, 12, and 18 hours of incubation increased significantly over time. In contrast, the numbers of Escherichia coli control strain recovered from macrophages declined at the same designated incubation times. Light and electron microscopy confirmed internalization, uptake, and multiplication of bacteria within spacious, clear vacuoles in the macrophages. Using acid phosphatase as a lysosomal marker, it was shown that P. damselae inhibits phagolysosomal fusion. Invasion and replication of P. damselae within epithelioma papillosum carpio (EPC), channel catfish ovary (CCO), and fathead minnow (FHM) cells lines was also evaluated using an in vitro invasion assay. All three cell lines were susceptible to invasion and supported replication of P. damselae. Fathead minnow cells were more susceptible to invasion than the other two cell lines as indicated by greater numbers of infected cells and recovered bacteria at time 0. Using light and electron microscopy, invasion of cells by bacteria was observed as early as 30 minutes after infection, and intracellular bacteria were observed in large, clear, membrane-bound vacuoles. The intracellular location of P. damselae was confirmed using ruthenium red staining to discriminate between the extra- and intra-cellular spaces. Using flow cytometry, results indicated that P. damselae induces apoptosis in phagocytes obtained from hybrid striped bass head kidney and after 12, 18, and 24 hours of incubation, the relative numbers of cells infected with P. damselae showing signs of apoptosis increased over time and were significantly greater than the controls. The relative numbers of apoptotic cells that were infected with the formalin-killed strain increased, but not significantly, above the control after the same designated times of incubation

Novel Clinical Campylobacter jejuni Infection Models Based on Sensitization of Mice to Lipooligosaccharide, a Major Bacterial Factor Triggering Innate Immune Responses in Human Campylobacteriosis

Human Campylobacter jejuni infections inducing campylobacteriosis including post-infectious sequelae such as Guillain-Barré syndrome and reactive arthritis are rising worldwide and progress into a global burden of high socioeconomic impact. Intestinal immunopathology underlying campylobacteriosis is a classical response of the innate immune system characterized by the accumulation of neutrophils and macrophages which cause tissue destruction, barrier defects and malabsorption leading to bloody diarrhea. Clinical studies revealed that enteritis and post-infectious morbidities of human C. jejuni infections are strongly dependent on the structure of pathogenic lipooligosaccharides (LOS) triggering the innate immune system via Toll-like-receptor (TLR)-4 signaling. Compared to humans, mice display an approximately 10,000 times weaker TLR-4 response and a pronounced colonization resistance (CR) against C. jejuni maintained by the murine gut microbiota. In consequence, investigations of campylobacteriosis have been hampered by the lack of experimental animal models. We here summarize recent progress made in the development of murine C. jejuni infection models that are based on the abolishment of CR by modulating the murine gut microbiota and by sensitization of mice to LOS. These advances support the major role of LOS driven innate immunity in pathogenesis of campylobacteriosis including post-infectious autoimmune diseases and promote the preclinical evaluation of novel pharmaceutical strategies for prophylaxis and treatment

Immunostimulatory effects and delivery of oligodeoxynucleotides containing CpG motifs (CpG-ODN) in neonatal broiler chickens

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) have been shown to stimulate the innate immune system against a variety of bacterial, viral, and protozoan infections in a variety of vertebrate species. The objectives of this study were to investigate the immunostimulatory effect of CpG-ODN against Salmonella Typhimurium infection and the formulation and delivery of CpG-ODN by the in ovo route. Day-old broiler chicks or embryonated eggs (day 18th of incubation) received either 50 &#61549;g of CpG-ODN, 50 &#61549;g of non-CpG-ODN, or saline. At day four-post hatch, all birds were subcutaneously inoculated by Salmonella Typhimurium. Clinical signs, pathology, bacterial isolations from the air sacs, and mortality were observed for ten days following challenge. The survival rate of the birds that received CpG-ODN via in ovo or in vivo treatments was significantly higher than the control group. Salmonella Typhimurium level in the peripheral blood and pathology were significantly lower (p < 0.001) in CpG-ODN group compared to the control group. In order to investigate the effect of formulation of CpG-ODN, embryonated eggs (day 18th of incubation) were inoculated with either 50 &#61549;g of CpG-ODN alone or CpG-ODN formulated with polyphosphazene, liposome, or Emulsigen®. Four days after administration of CpG-ODN formulations, the birds were challenged with E. coli by subcutaneous injection. Clinical signs, pathology, bacterial isolations from the air sacs, and mortality were observed for seven days following challenge. The birds that received either CpG-ODN or CpG-ODN formulated with polyphosphazene had significantly higher survival rates (30 and 60%) compared to the birds in groups receiving either non-CpG-ODN or saline. Bacterial loads in the air sacs were lower in groups treated with formulated CpG-ODN compared to the CpG-ODN alone or control groups. However, formulation of CpG-ODN with liposomes or Emulsigen® did not increase the immunoprotective effect against E. coli infection. We showed that treatment with CpG-ODN protects neonatal chickens against an intracellular bacterial infection and that co-treatment of CpG-ODN with polyphosphazene enhances the immunoprotective effect of CpG-ODN

The role of type I interferons (IFNs) in the regulation of chicken macrophage inflammatory response to bacterial challenge

International audienceMammalian type I interferons (IFNα/β) are known to modulate inflammatory processes in addition to their antiviral properties. Indeed, virus-induced type I interferons regulate the mammalian phagocyte immune response to bacteria during superinfections. However, it remains unresolved whether type I IFNs similarly impact the chicken macrophage immune response. We first evidenced that IFNα and IFNβ act differently in terms of gene expression stimulation and activation of intracellular signaling pathways in chicken macrophages. Next, we showed that priming of chicken macrophages with IFNα increased bacteria uptake, boosted bacterial-induced ROS/NO production and led to an increased transcriptional expression or production of NOS2/NO, IL1B/IL-1β and notably IFNB/IFNβ. Neutralization of IFNβ during bacterial challenge limited IFNα-induced augmentation of the pro-inflammatory response. In conclusion, we demonstrated that type I IFNs differently regulate chicken macrophage functions and drive a pro-inflammatory response to bacterial challenge. These findings shed light on the diverse functions of type I IFNs in chicken macrophages