Torsion of the caudate lobe of the liver and concurrent necrohemorrhagic typhlocolitis in a zoo-housed Patagonian mara.

Liver lobe torsion has been reported in many species, with frequent reports in rabbits. Here we describe caudate liver lobe torsion and concurrent necrohemorrhagic typhlocolitis in a Patagonian mara (syn: Patagonian cavy, Patagonian hare, Dolichotis patagonum). Following acute death, postmortem examination findings included torsion of the hepatic caudate process, which had fibrous adhesions to the pancreas indicating chronicity. The cecal apex and proximal 30 cm of colon had regionally reddened serosa and diffusely roughened and reddened mucosa with brown-red and granular luminal contents. Key histologic findings included massive necrosis of the torsed hepatic caudate lobe, consistent with infarction, necrotizing hepatitis in remaining areas of liver, necrohemorrhagic typhlocolitis, adrenocortical necrosis and hemorrhage, and renal tubular degeneration and necrosis with tubular casts. Bacterial culture of cecal contents yielded pure growth of Salmonella spp. Death was attributed to toxemia or bacteremia resulting from Salmonella spp. infection, as the hepatic lobe torsion appeared chronic. It was undetermined if the liver lobe torsion predisposed to gastrointestinal compromise and infection. Patagonian maras have some anatomical similarities to rabbits and are highly cursorial, not dissimilar to hares, Lepus spp. We speculate that these characteristics may increase the likelihood of hepatic caudate lobe torsion in this species.

Systemic salmonellosis in 4 cats.

Clinical signs in 4 cases of salmonellosis in cats included vomiting, diarrhea (2 cases each), fever, dystocia, icterus, and seizures (1 case each). Three cats died, and one was euthanized. Grossly, all cats were in poor body condition and had yellow-to-dark-red perianal feces (3 cases), oral and ocular pallor (2 cases) or icterus (1 case), fluid or pasty yellow intestinal contents (4 cases), white or dark-red-to-black depressed areas on the hepatic surface (2 cases), yellow abdominal fluid with swollen abdominal lymph nodes (1 case), and fibrin strands on the placental chorionic surface (1 case). Histologically, all cats had necrotizing enterocolitis and random hepatocellular necrosis. Other histologic findings included mesenteric (4 cases) or splenic (2 cases) lymphoid necrosis, and endometrial and chorioallantoic necrosis (1 case). Gram-negative bacilli were observed within neutrophils and macrophages in the intestinal lamina propria (4 cases), liver, spleen, lymph node, endometrium, and placenta (1 case each). Aerobic bacterial culture on frozen samples of small intestine, mesenteric lymph node, lung, and liver yielded Salmonella enterica subsp. enterica. Serotyping was consistent with S. Enteritidis (cases 1, 3) and S. Typhimurium (cases 2, 4).

Pathology of Salmonella enterica Subspecies enterica Serotype Typhimurium Infection in Chinchillas (Chinchilla lanigera).

Septicaemia is the main pathological manifestation of Salmonella infection in chinchillas (Chinchilla lanigera), although information on its pathology is limited. We now describe the gross, histological and immunohistochemical features of Salmonella enterica subspecies enterica serotype Typhimurium (S. Typhimurium) infection in ranched chinchillas. Eighty-five adult pregnant chinchillas had anorexia, prostration, weight loss, hyperthermia and abortion. Necropsy of 13 animals revealed splenomegaly, hepatomegaly, mesenteric lymphadenomegaly, prominent Peyer's patches, pulmonary oedema, white pinpoint lesions in multiple organs and petechiae in the urinary bladder. In all cases, histological lesions were consistent with septicaemia, characterized by acute necrotizing hepatitis, splenitis, lymphadenitis, cystitis, pneumonia, enterocolitis, gastritis and/or nephritis. Immunohistochemistry for Salmonella spp on seven cases revealed intralesional immunolabelling in all affected organs. Salmonella sp was isolated from liver, spleen, intestinal contents and blood of 10 chinchillas. Isolates of four animals were identified as S. Typhimurium.

Aryl Hydrocarbon Receptor Activation by Benzo[a]pyrene Prevents Development of Septic Shock and Fatal Outcome in a Mouse Model of Systemic Salmonella enterica Infection.

This study focused on immunomodulatory effects of aryl hydrocarbon receptor (AhR) activation through benzo[a]pyrene (BaP) during systemic bacterial infection. Using a well-established mouse model of systemic Salmonella enterica (S.E.) infection, we studied the influence of BaP on the cellular and humoral immune response and the outcome of disease. BaP exposure significantly reduced mortality, which is mainly caused by septic shock. Surprisingly, the bacterial burden in BaP-exposed surviving mice was significantly higher compared to non-exposed mice. During the early phase of infection (days 1-3 post-infection (p.i.)), the transcription of proinflammatory factors (i.e., IL-12, IFN-γ, TNF-α, IL-1ß, IL-6, IL-18) was induced faster under BaP exposure. Moreover, BaP supported the activity of antigen-presenting cells (i.e., CD64 (FcγRI), MHC II, NO radicals, phagocytosis) at the site of infection. However, early in infection, the anti-inflammatory cytokines IL-10 and IL-22 were also locally and systemically upregulated in BaP-exposed S.E.-infected mice. BaP-exposure resulted in long-term persistence of salmonellae up to day 90 p.i., which was accompanied by significantly elevated S.E.-specific antibody responses (i.e., IgG1, IgG2c). In summary, these data suggest that BaP-induced AhR activation is capable of preventing a fatal outcome of systemic S.E. infection, but may result in long-term bacterial persistence, which, in turn, may support the development of chronic inflammation.

Salmonella enterica serovar Typhimurium uses anaerobic respiration to overcome propionate-mediated colonization resistance.

The gut microbiota benefits the host by limiting enteric pathogen expansion (colonization resistance), partially via the production of inhibitory metabolites. Propionate, a short-chain fatty acid produced by microbiota members, is proposed to mediate colonization resistance against Salmonella enterica serovar Typhimurium (S. Tm). Here, we show that S. Tm overcomes the inhibitory effects of propionate by using it as a carbon source for anaerobic respiration. We determine that propionate metabolism provides an inflammation-dependent colonization advantage to S. Tm during infection. Such benefit is abolished in the intestinal lumen of Salmonella-infected germ-free mice. Interestingly, S. Tm propionate-mediated intestinal expansion is restored when germ-free mice are monocolonized with Bacteroides thetaiotaomicron (B. theta), a prominent propionate producer in the gut, but not when mice are monocolonized with a propionate-production-deficient B. theta strain. Taken together, our results reveal a strategy used by S. Tm to mitigate colonization resistance by metabolizing microbiota-derived propionate.

Streptozotocin-induced hyperglycemia alters the cecal metabolome and exacerbates antibiotic-induced dysbiosis.

It is well established in the microbiome field that antibiotic (ATB) use and metabolic disease both impact the structure and function of the gut microbiome. But how host and microbial metabolism interacts with ATB susceptibility to affect the resulting dysbiosis remains poorly understood. In a streptozotocin-induced model of hyperglycemia (HG), we use a combined metagenomic, metatranscriptomic, and metabolomic approach to profile changes in microbiome taxonomic composition, transcriptional activity, and metabolite abundance both pre- and post-ATB challenge. We find that HG impacts both microbiome structure and metabolism, ultimately increasing susceptibility to amoxicillin. HG exacerbates drug-induced dysbiosis and increases both phosphotransferase system activity and energy catabolism compared to controls. Finally, HG and ATB co-treatment increases pathogen susceptibility and reduces survival in a Salmonella enterica infection model. Our data demonstrate that induced HG is sufficient to modify the cecal metabolite pool, worsen the severity of ATB dysbiosis, and decrease colonization resistance.

Host metabolic shift during systemic Salmonella infection revealed by comparative proteomics.

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a food-borne bacterium that causes acute gastroenteritis in humans and typhoid fever in mice. Salmonella pathogenicity island II (SPI-2) is an important virulence gene cluster responsible for Salmonella survival and replication within host cells, leading to systemic infection. Previous studies have suggested that SPI-2 function to modulate host vesicle trafficking and immune response to promote systemic infection. However, the molecular mechanism and the host responses triggered by SPI-2 remain largely unknown. To assess the roles of SPI-2, we used a differential proteomic approach to analyse host proteins levels during systemic infections in mice. Our results showed that infection by WT S. Typhimurium triggered the reprogramming of host cell metabolism and inflammatory response. Salmonella systemic infection induces an up-regulation of glycolytic process and a repression of the tricarboxylic acid (TCA) cycle. WT-infected tissues prefer to produce adenosine 5'-triphosphate (ATP) through aerobic glycolysis rather than relying on oxidative phosphorylation to generate energy. Moreover, our data also revealed that infected macrophages may undergo both M1 and M2 polarization. In addition, our results further suggest that SPI-2 is involved in altering actin cytoskeleton to facilitate the Salmonella-containing vacuole (SCV) biogenesis and perhaps even the release of bacteria later in the infection process. Results from our study provide valuable insights into the roles of SPI-2 during systemic Salmonella infection and will guide future studies to dissect the molecular mechanisms of how SPI-2 functions in vivo.

Fasting increases microbiome-based colonization resistance and reduces host inflammatory responses during an enteric bacterial infection.

Reducing food intake is a common host response to infection, yet it remains unclear whether fasting is detrimental or beneficial to an infected host. Despite the gastrointestinal tract being the primary site of nutrient uptake and a common route for infection, studies have yet to examine how fasting alters the host's response to an enteric infection. To test this, mice were fasted before and during oral infection with the invasive bacterium Salmonella enterica serovar Typhimurium. Fasting dramatically interrupted infection and subsequent gastroenteritis by suppressing Salmonella's SPI-1 virulence program, preventing invasion of the gut epithelium. Virulence suppression depended on the gut microbiota, as Salmonella's invasion of the epithelium proceeded in fasting gnotobiotic mice. Despite Salmonella's restored virulence within the intestines of gnotobiotic mice, fasting downregulated pro-inflammatory signaling, greatly reducing intestinal pathology. Our study highlights how food intake controls the complex relationship between host, pathogen and gut microbiota during an enteric infection.

An Outbreak of Pullorum Disease in a Young Layer Parent Flock in Austria Presented with Central Nervous System Signs.

The present report describes an outbreak of Pullorum disease in a young layer parent stock in Austria. The flock, which comprised 14,220 Lohmann brown layer chickens, experienced high mortality from the first week of life, reaching a total of 1905 chickens in the fifth week, when the flock was depopulated. Clinical signs included uneven size of the chicks, pasty vents, apathy, and diminished water and feed intake, with some birds presenting central nervous system signs such as tremors and torticollis. The postmortem investigation of 43 birds, of ages 1 to 4 weeks, revealed retained yolk sacs filled with caseous exudate, purulent airsacculitis, hepatitis with whitish pinpoint coalescing necrotic foci, splenitis with splenomegaly, hemorrhagic-mucoid enteritis in the small intestine, fibrinous typhlitis, nephromegaly, and urate deposits in the ureters and cloaca. Inflammation and/or necrosis were identified in liver, spleen, kidney, small intestine, and heart by histopathology. However, no histopathologic lesions were observed in the brain. Salmonella enterica was isolated from heart, liver, spleen, and brain in pure culture. Group-specific serotyping determined the presence of group D, with S. enterica subspecies enterica serovar Gallinarum being confirmed based on the Kauffmann-White scheme. A duplex PCR further identified S. enterica subspecies enterica serovar Gallinarum biovar Pullorum as the responsible agent for the outbreak. Subsequently, the grandparent flocks, from which the affected flock originated, were tested and found to be negative for Salmonella Pullorum, with no other progenies from the same grandparents developing disease. Although the source of the pathogen could not be identified, such findings highlight the importance of "old" pathogens such as Salmonella Pullorum causing sudden high mortality in chicks, even in a highly controlled environment.

Reporte de caso­Brote de pulorosis en una parvada de reproductores de postura jóvenes en Austria que presentó signos del sistema nervioso central. El presente reporte describe un brote de pulorosis en un lote de reproductoras de postura jóvenes en Austria. La parvada, que comprendió 14,220 gallinas de postura Lohmann, experimentó alta mortalidad desde la primera semana de vida, alcanzando un total de 1905 gallinas en la quinta semana, cuando la parvada se despobló. Los signos clínicos incluyeron tamaño desigual de pollito, empastamiento de la cloaca, apatía y disminución del consumo de agua y alimento, y algunas aves presentaron signos del sistema nervioso central como temblores y tortícolis. La investigación post mórtem de 43 aves, de 1 a 4 semanas de edad, reveló sacos vitelinos retenidos llenos de exudado caseoso, aerosaculitis purulenta, hepatitis con focos necróticos coalescentes blanquecinos, esplenitis con esplenomegalia, enteritis hemorrágica-mucoide en el intestino delgado, tiflitis fibrinosa, nefromegalia y depósitos de uratos en los uréteres y cloaca. Se identificaron inflamación y/o necrosis en hígado, bazo, riñón, intestino delgado y corazón mediante histopatología. Sin embargo, no se observaron lesiones histopatológicas en el cerebro. Se aisló Salmonella enterica de corazón, hígado, bazo y cerebro en cultivo puro. La serotipificación específica de grupo determinó la presencia del grupo D, con S entérica subespecie enterica serovar Gallinarum que se confirmó según el esquema de Kauffmann-White. Un método dúplex de PCR identificó S. enterica subspecie enterica serovar Pullorum como el agente responsable del brote. Posteriormente, las parvadas de abuelas, de las que se originó la parvada afectada, fueron analizadas y resultaron negativas para Salmonella Pullorum, sin que ninguna otra progenie de los mismos abuelos desarrollara la enfermedad. Aunque no se pudo identificar la fuente del patógeno, tales hallazgos resaltan la importancia de patógenos "viejos" como Salmonella Pullorum que causan una alta mortalidad repentina en los pollitos, incluso en un ambiente altamente controlado.

Pathological and Microbiological Findings in Fatal Cases of Salmonellosis in Captive Bothrops Snakes in Southern Brazil.

Salmonella spp. are gram-negative commensal bacteria of vertebrates, including reptiles. Infected snakes may be asymptomatic or manifest clinical disease and death, especially after stressful events. Salmonellosis was diagnosed in 10 captive snakes from the Bothrops genus. The most frequent changes were emaciation (8/10), fibrinonecrotic or granulomatous hepatitis (8/9), fibrinonecrotic or granulomatous enterocolitis (8/9), necrotic and heterophilic myocarditis (2/10), fibrinonecrotic or granulomatous pancreatitis (2/5), fibrinoheterophilic osteomyelitis (1/10), fibrinous and pyogranulomatous pericarditis (1/10) and granulomatous splenitis (1/6). Salmonella enterica was isolated from six cases. The subspecies identified were arizonae (3/6), diarizonae (1/6) and houtenae (1/6), in addition to the serotype Typhimurium (1/6). In cases without isolation, there was immunolabelling of Salmonella spp. in intestinal (3/4), hepatic (1/4) and cardiac (1/4) lesions.

The atypical small GTPase GEM/Kir is a negative regulator of the NADPH oxidase and NETs production through macroautophagy.

Despite the important function of neutrophils in the eradication of infections and induction of inflammation, the molecular mechanisms regulating the activation and termination of the neutrophil immune response is not well understood. Here, the function of the small GTPase from the RGK family, Gem, is characterized as a negative regulator of the NADPH oxidase through autophagy regulation. Gem knockout (Gem KO) neutrophils show increased NADPH oxidase activation and increased production of extracellular and intracellular reactive oxygen species (ROS). Enhanced ROS production in Gem KO neutrophils was associated with increased NADPH oxidase complex-assembly as determined by quantitative super-resolution microscopy, but normal exocytosis of gelatinase and azurophilic granules. Gem-deficiency was associated with increased basal autophagosomes and autolysosome numbers but decreased autophagic flux under phorbol ester-induced conditions. Neutrophil stimulation triggered the localization of the NADPH oxidase subunits p22phox and p47phox at LC3-positive structures suggesting that the assembled NADPH oxidase complex is recruited to autophagosomes, which was significantly increased in Gem KO neutrophils. Prevention of new autophagosome formation by treatment with SAR405 increased ROS production while induction of autophagy by Torin-1 decreased ROS production in Gem KO neutrophils, and also in wild-type neutrophils, suggesting that macroautophagy contributes to the termination of NADPH oxidase activity. Autophagy inhibition decreased NETs formation independently of enhanced ROS production. NETs production, which was significantly increased in Gem-deficient neutrophils, was decreased by inhibition of both autophagy and calmodulin, a known GEM interactor. Intracellular ROS production was increased in Gem KO neutrophils challenged with live Gram-negative bacteria Pseudomonas aeruginosa or Salmonella Typhimurium, but phagocytosis was not affected in Gem-deficient cells. In vivo analysis in a model of Salmonella Typhimurium infection indicates that Gem-deficiency provides a genetic advantage manifested as a moderate increased in survival to infections. Altogether, the data suggest that Gem-deficiency leads to the enhancement of the neutrophil innate immune response by increasing NADPH oxidase assembly and NETs production and that macroautophagy differentially regulates ROS and NETs in neutrophils.

Heat stress inhibits expression of the cytokines, and NF-κB-NLRP3 signaling pathway in broiler chickens infected with salmonella typhimurium.

High ambient temperature has potential influence on oxidative stress, or systemic inflammation affecting poultry production and immune status of chickens. Heat stress (HS) induces intestinal inflammation and increases susceptibility of harmful pathogens, such as Salmonella and Escherichia coli. Intestinal inflammation is a common result of body immune dysfunction. Therefore, we designed an experiment to analyze the effects of 35 ± 2 °C HS on salmonella infection in chickens through regulation of the immune responses. 40 broiler chickens were randomly divided into 4 groups: control group, heat stress (HS) group, salmonella typhimurium (ST) group and model group (heat stress + salmonella typhimurium, HS + ST). Birds in HS and model group were treated with 35 ± 2 °C heat stress 6 h a day and for 14 continuous days. Then, ST and model group birds were orally administrated with 1 mL ST inoculum (109 cfu/mL). Chickens were sacrificed at the 4th day after ST administration and ileum tissues were measured. We observed that heat stress decreased ileum TNF-α and IL-1ß protein expressions. Concomitantly heat stress decreased NLRP3 and Caspase-1 protein levels. The protein expressions of p-NF-κB-p65 and p-IκB-α in ileum. Heat stress also inhibited IFN-α, p-IRF3 and p-TBK1, showing a deficiency in the HS + ST group birds. Together, the present data suggested that heat stress suppressed intestinal immune activity in chickens infected by salmonella typhimurium, as observed by the decrease of immune cytokines levels, which regulated by NF-κB-NLRP3 signaling pathway.

Genetic variation in the MacAB-TolC efflux pump influences pathogenesis of invasive Salmonella isolates from Africa.

The various sub-species of Salmonella enterica cause a range of disease in human hosts. The human-adapted Salmonella enterica serovar Typhi enters the gastrointestinal tract and invades systemic sites to cause enteric (typhoid) fever. In contrast, most non-typhoidal serovars of Salmonella are primarily restricted to gut tissues. Across Africa, invasive non-typhoidal Salmonella (iNTS) have emerged with an ability to spread beyond the gastrointestinal tract and cause systemic bloodstream infections with increased morbidity and mortality. To investigate this evolution in pathogenesis, we compared the genomes of African iNTS isolates with other Salmonella enterica serovar Typhimurium and identified several macA and macB gene variants unique to African iNTS. MacAB forms a tripartite efflux pump with TolC and is implicated in Salmonella pathogenesis. We show that macAB transcription is upregulated during macrophage infection and after antimicrobial peptide exposure, with macAB transcription being supported by the PhoP/Q two-component system. Constitutive expression of macAB improves survival of Salmonella in the presence of the antimicrobial peptide C18G. Furthermore, these macAB variants affect replication in macrophages and influence fitness during colonization of the murine gastrointestinal tract. Importantly, the infection outcome resulting from these macAB variants depends upon both the Salmonella Typhimurium genetic background and the host gene Nramp1, an important determinant of innate resistance to intracellular bacterial infection. The variations we have identified in the MacAB-TolC efflux pump in African iNTS may reflect evolution within human host populations that are compromised in their ability to clear intracellular Salmonella infections.

YAP in epithelium senses gut barrier loss to deploy defenses against pathogens.

Pathogens commonly disrupt the intestinal epithelial barrier; however, how the epithelial immune system senses the loss of intestinal barrier as a danger signal to activate self-defense is unclear. Through an unbiased approach in the model nematode Caenorhabditis elegans, we found that the EGL-44/TEAD transcription factor and its transcriptional activator YAP-1/YAP (Yes-associated protein) were activated when the intestinal barrier was disrupted by infections with the pathogenic bacterium Pseudomonas aeruginosa PA14. Gene Ontology enrichment analysis of the genes containing the TEAD-binding sites revealed that "innate immune response" and "defense response to Gram-negative bacterium" were two top significantly overrepresented terms. Genetic inactivation of yap-1 and egl-44 significantly reduced the survival rate and promoted bacterial accumulation in worms after bacterial infections. Furthermore, we found that disturbance of the E-cadherin-based adherens junction triggered the nuclear translocation and activation of YAP-1/YAP in the gut of worms. Although YAP is a major downstream effector of the Hippo signaling, our study revealed that the activation of YAP-1/YAP was independent of the Hippo pathway during disruption of intestinal barrier. After screening 10 serine/threonine phosphatases, we identified that PP2A phosphatase was involved in the activation of YAP-1/YAP after intestinal barrier loss induced by bacterial infections. Additionally, our study demonstrated that the function of YAP was evolutionarily conserved in mice. Our study highlights how the intestinal epithelium recognizes the loss of the epithelial barrier as a danger signal to deploy defenses against pathogens, uncovering an immune surveillance program in the intestinal epithelium.

Pathogenicity of clinical Salmonella enterica serovar Typhimurium isolates from Thailand in a mouse colitis model.

Salmonella enterica serovar Typhimurium (S. Typhimurium [STM]) is a leading cause of nontyphoidal salmonellosis (NTS) worldwide. The pathogenesis of NTS has been studied extensively using a streptomycin-pretreated mouse colitis model with the limited numbers of laboratory STM strains. However, the pathogenicity of the clinically isolated STM (STMC) strains endemic in Thailand in mice has not been explored. The aim of this study was to compare the pathogenicity of STMC strains collected from Northern Thailand with the laboratory STM (IR715) in mice. Five STMC isolates were obtained from the stool cultures of patients with acute NTS admitted to Maharaj Nakorn Chiang Mai Hospital in 2016 and 2017. Detection of virulence genes and sequence type (ST) of the strains was performed. Female C57BL/6 mice were pretreated with streptomycin sulfate 1 day prior to oral infection with STM. On Day 4 postinfection, mice were euthanized, and tissues were collected to analyze the bacterial numbers, tissue inflammation, and cecal histopathological score. We found that all five STMC strains are ST34 and conferred the same or reduced pathogenicity compared with that of IR715 in mice. A strain-specific effect of ST34 on mouse gut colonization was also observed. Thailand STM ST34 exhibited a significant attenuated systemic infection in mice possibly due to the lack of spvABC-containing virulence plasmid.

Immune modulations and survival strategies of evolved hypervirulent Salmonella Typhimurium strains.

BACKGROUND: Evolving multidrug-resistance and hypervirulence in Salmonella is due to multiple host-pathogen, and non-host environmental interactions. Previously we had studied Salmonella adaptation upon repeated exposure in different in-vitro and in-vivo environmental conditions. This study deals with the mechanistic basis of hypervirulence of the passaged hypervirulent Salmonella strains reported previously. METHODS: Real-time PCR, flow cytometry, western blotting, and confocal microscopy were employed to check the alteration of signaling pathways by the hypervirulent strains. The hypervirulence was also looked in-vivo in the Balb/c murine model system. RESULTS: The hypervirulent strains altered cytokine production towards anti-inflammatory response via NF-κB and Akt-NLRC4 signaling in RAW-264.7 and U-937 cells. They also impaired lysosome number, as well as co-localization with the lysosome as compared to unpassaged WT-STM. In Balb/c mice also they caused decreased antimicrobial peptides, reduced nitric oxide level, altered cytokine production, and reduced CD4+ T cell population leading to increased organ burden. CONCLUSIONS: Hypervirulent Salmonella strains infection resulted in an anti-inflammatory environment by upregulating IL-10 and down-regulating IL-1ß expression. They also evaded lysosomal degradation for their survival. With inhibition of NF-κB and Akt signaling, cytokine expression, lysosome number, as well as the bacterial burden was reverted, indicating the infection mediated immune modulation by the hypervirulent Salmonella strains through these pathways. GENERAL SIGNIFICANCE: Understanding the mechanism of adaptation can provide better disease prognosis by either targeting the bacterial gene or by strengthening the host immune system that might ultimately help in controlling salmonellosis.

Salmonella Persistence and Host Immunity Are Dictated by the Anatomical Microenvironment.

The intracellular bacterial pathogen Salmonella is able to evade the immune system and persist within the host. In some cases, these persistent infections are asymptomatic for long periods and represent a significant public health hazard because the hosts are potential chronic carriers, yet the mechanisms that control persistence are incompletely understood. Using a mouse model of chronic typhoid fever combined with major histocompatibility complex (MHC) class II tetramers to interrogate endogenous, Salmonella-specific CD4+ helper T cells, we show that certain host microenvironments may favorably contribute to a pathogen's ability to persist in vivo We demonstrate that the environment in the hepatobiliary system may contribute to the persistence of Salmonella enterica subsp. enterica serovar Typhimurium through liver-resident immunoregulatory CD4+ helper T cells, alternatively activated macrophages, and impaired bactericidal activity. This contrasts with lymphoid organs, such as the spleen and mesenteric lymph nodes, where these same cells appear to have a greater capacity for bacterial killing, which may contribute to control of bacteria in these organs. We also found that, following an extended period of infection of more than 2 years, the liver appeared to be the only site that harbored Salmonella bacteria. This work establishes a potential role for nonlymphoid organ immunity in regulating chronic bacterial infections and provides further evidence for the hepatobiliary system as the site of chronic Salmonella infection.

The HOIL-1L ligase modulates immune signalling and cell death via monoubiquitination of LUBAC.

The linear ubiquitin chain assembly complex (LUBAC), which consists of HOIP, SHARPIN and HOIL-1L, promotes NF-κB activation and protects against cell death by generating linear ubiquitin chains. LUBAC contains two RING-IBR-RING (RBR) ubiquitin ligases (E3), and the HOIP RBR is responsible for catalysing linear ubiquitination. We found that HOIL-1L RBR plays a crucial role in regulating LUBAC. HOIL-1L RBR conjugates monoubiquitin onto all LUBAC subunits, followed by HOIP-mediated conjugation of linear chains onto monoubiquitin, and these linear chains attenuate the functions of LUBAC. The introduction of E3-defective HOIL-1L mutants into cells augmented linear ubiquitination, which protected the cells against Salmonella infection and cured dermatitis caused by reduced LUBAC levels due to SHARPIN loss. Our results reveal a regulatory mode of E3 ligases in which the accessory E3 in LUBAC downregulates the main E3 by providing preferred substrates for autolinear ubiquitination. Thus, inhibition of HOIL-1L E3 represents a promising strategy for treating severe infections or immunodeficiency.

Salmonellosis in Hedgehogs.

African pygmy hedgehogs are popular pets worldwide. The knowledge and understanding of pet hedgehog common veterinary conditions are increasing as new information and research are published; however, there is still much to learn about this fascinating animal. Salmonella is one of the most common zoonoses worldwide and is naturally isolated from the intestinal tract of many animal species, including hedgehogs. This article discusses the cause, clinical signs, diagnosis, treatment, and prevention of salmonella infection in hedgehogs, primarily focusing on African pygmy hedgehogs, with some reference to European hedgehogs.

NLRC4 inflammasome activation is NLRP3- and phosphorylation-independent during infection and does not protect from melanoma.

The NAIP/NLRC4 inflammasome is a cytosolic sensor of bacteria that activates caspase-1 and initiates potent immune responses. Structural, biochemical, and genetic data demonstrate that NAIP proteins are receptors for bacterial ligands, while NLRC4 is a downstream adaptor that multimerizes with NAIPs to form an inflammasome. NLRC4 has also been proposed to suppress tumor growth, though the underlying mechanism is unknown. Further, NLRC4 is phosphorylated on serine 533, which was suggested to be critical for its function. In the absence of S533 phosphorylation, it was proposed that another inflammasome protein, NLRP3, can induce NLRC4 activation. We generated a new Nlrc4-deficient mouse line and mice with S533D phosphomimetic or S533A nonphosphorylatable NLRC4. Using these models in vivo and in vitro, we fail to observe a requirement for phosphorylation in NLRC4 inflammasome function. Furthermore, we find no role for NLRP3 in NLRC4 function, or for NLRC4 in a model of melanoma. These results clarify our understanding of the mechanism and biological functions of NAIP/NLRC4 activation.