Visiting the cell biology of Salmonella infection

Effects of Salmonella Outer Membrane Vesicles on Intestinal Microbiota and Intestinal Barrier Function

Salmonella enterica is one of the most important zoonotic pathogens causing foodborne gastroenteritis worldwide. Outer membrane vesicles (OMVs) are lipid-bilayer vesicles produced by Gram-negative bacteria, which contain biologically active components. We hypothesized that OMVs are an important weapon of S. enterica to initiate enteric diseases pathologies. In this study, the effects of S. enterica OMVs (SeOMVs) on intestinal microbiota and intestinal barrier function were investigated. In vitro fecal culture experiments showed that alpha diversity indexes and microbiota composition were altered by SeOMV supplementation. SeOMV supplementation showed an increase of pH, a decrease of OD630 and total short chain fatty acid (SCFA) concentrations. In vitro IPEC-J2 cells culture experiments showed that SeOMV supplementation did not affect the IPEC-J2 cell viability and the indicated genes expression. In vivo experiments in mice showed that SeOMVs had adverse effects on average daily gain (p < 0.05) and feed:gain ratio (p < 0.05), and had a tendency to decrease the final body weight (p = 0.073) in mice. SeOMV administration decreased serum interleukin-10 level (p < 0.05), decreased the relative abundance of bacteria belonging to the genera BacC-u-018 and Akkermansia (p < 0.05). Furthermore, SeOMV administration damaged the ileum mucosa (p < 0.05). These findings suggest that SeOMVs play an important role in the activation of intestinal inflammatory response induced by S. enterica, and downregulation of SCFA-producing bacteria is a possible mechanism.

Spermidine constitutes a key determinant of motility and attachment of Salmonella Typhimurium through a novel regulatory mechanism

Spermidine is a poly-cationic molecule belonging to the family of polyamines and is ubiquitously present in all organisms. Salmonella synthesizes, and harbours specialized transporters to import spermidine. A group of polyamines have been shown to assist in Salmonella Typhimurium's virulence and regulation of Salmonella pathogenicity Inslad 1 (SPI-1) genes and stress resistance; however, the mechanism remains elusive. The virulence trait of Salmonella depends on its ability to employ multiple surface structures to attach and adhere to the surface of the target cells before invasion and colonization of the host niche. Our study discovers the mechanism by which spermidine assists in the early stages of Salmonella pathogenesis. For the first time, we report that Salmonella Typhimurium regulates spermidine transport and biosynthesis processes in a mutually inclusive manner. Using a mouse model, we show that spermidine is critical for invasion into the murine Peyer's patches, which further validated our in vitro cell line observation. We show that spermidine controls the mRNA expression of fimbrial (fimA) and non-fimbrial adhesins (siiE, pagN) in Salmonella and thereby assists in attachment to host cell surfaces. Spermidine also regulated the motility through the expression of flagellin genes by enhancing the translation of sigma-28, which features an unusual start codon and a poor Shine-Dalgarno sequence. Besides regulating the formation of the adhesive structures, spermidine tunes the expression of the two-component system BarA/SirA to regulate SPI-1 encoded genes. Thus, our study unravels a novel regulatory mechanism by which spermidine exerts critical functions during Salmonella Typhimurium pathogenesis.

Subversion strategies of lysosomal killing by intracellular pathogens

Many pathogenic organisms need to reach either an intracellular compartment or the cytoplasm of a target cell for their survival, replication or immune system evasion. Intracellular pathogens frequently penetrate into the cell through the endocytic and phagocytic pathways (clathrin-mediated endocytosis, phagocytosis and macropinocytosis) that culminates in fusion with lysosomes. However, several mechanisms are triggered by pathogenic microorganisms - protozoan, bacteria, virus and fungus - to avoid destruction by lysosome fusion, such as rupture of the phagosome and thereby release into the cytoplasm, avoidance of autophagy, delaying in both phagolysosome biogenesis and phagosomal maturation and survival/replication inside the phagolysosome. Here we reviewed the main data dealing with phagosome maturation and evasion from lysosomal killing by different bacteria, protozoa, fungi and virus.

Clinical and microbiological characterization of Salmonella spp. isolates from patients treated in a university hospital in South America between 2012-2021: a cohort study

BACKGROUND

Salmonellosis is a major cause of morbidity and mortality and one of the most frequent etiologies of diarrhea in the world. Mortality due to Salmonellosis in Latin America still poorly understood, and there is a lack of studies that evaluate resistance and clinical manifestations. The aims of this study were to characterize patients infected with Salmonella spp. seen in a university hospital in Colombia between 2012 and 2021, to evaluate trends in antibiotic resistance and to determine the proportion of overall mortality and related factors.

METHODS

Retrospective observational study. All patients with microbiological diagnosis of Salmonella spp. were included. The sociodemographic, clinical and microbiological characteristics were described, and the proportion of antibiotic resistant isolates per year was estimated. The prevalence of mortality according to age groups was calculated. Log binomial regression models were used to establish factors associated with mortality.

RESULTS

Five hundred twenty-two patients were analyzed. Salmonellosis accounted for 0.01% of all medical consultations. The median age was 16 years old. The most common clinical presentation was gastroenteric syndrome (77.1%) and symptoms included diarrhea (79.1%), fever (66.7%), abdominal pain (39.6%) and vomiting (35.2%). Of the Salmonella spp. isolates, 78.2% were not classified, 19.1% corresponded to non-typhoidal Salmonella and 2.7% to Salmonella typhi. Mortality occurs in 4.02% of the patients and was higher in patients with hematologic malignancy (11.6%). When analyzing by age group, the proportion of deaths was 2.8% in patients aged 15 years or younger, while in those older than 15 years it was 5.4%. Factors associated to mortality where bacteremia (aPR = 3.41 CI95%: 1.08-10.76) and to require treatment in the ICU (aPR = 8.13 CI95%: 1.82-37.76). In the last 10 years there has been a steady increase in resistance rates to ciprofloxacin, ampicillin, ampicillin/sulbactam and ceftriaxone, reaching rates above 60% in recent years.

CONCLUSIONS

Despite improved availability of antibiotics for the treatment of salmonellosis in the past decades, mortality due to salmonellosis continues occurring in children and adults, mainly in patients with hematological malignancies and bacteremia. Antibiotic resistance rates have increased significantly over the last 10 years. Public health strategies for the control of this disease should be strengthened, especially in vulnerable populations.

Refractory Salmonella Prosthetic Valve Endocarditis Complicated by Splenic Infarction and Aortic Pseudoaneurysm in a Patient with Double Prosthetic Valves: A Case Report

Endocarditis is an extremely rare complication of Salmonellosis with an incidence of 0.2–0.4%. It is a destructive and invasive infection that follows a highly complicated course and carries a high mortality rate that exceeds 45%. Multiple predisposing factors for Salmonella endocarditis have been described in the literature, including human immunodeficiency virus infection, congenital heart diseases, and the presence of a prosthetic valve. Herein, we report a case of Salmonella prosthetic valve endocarditis complicated by splenic infarction and aortic pseudoaneurysm presenting as a month-long history of fluctuating fever, chills, and rigors, accompanied by occasional cough and shortness of breath in a 55-year-old female with aortic and mitral valves replacement and multiple comorbidities. She was diagnosed by multiple radiographic studies and successfully treated with the Commando procedure and a long course of IV antibiotics.

A Mouse Infection Model with a Wildtype Salmonella enterica Serovar Typhimurium Strain for the Analysis of Inflammatory Innate Immune Cells

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a Gram-negative, facultative intracellular bacterium, which causes gastrointestinal disorders in humans, and systemic, typhoid fever-like infections in mice. Our current knowledge regarding the involvement of cellular and humoral immunity in the defense from S. Typhimurium infections is largely based on animal models with attenuated strains. Cells of the innate immune system act as one of the first barriers in the defense from bacteria. We established a robust experimental model for the characterization of these cell types and their response during host-pathogen interactions. Therefore, this protocol focuses on the characterization of macrophages, monocytes, and neutrophils in the spleens of infected animals by employing multi-color flow cytometry.

Spatiotemporal evaporating droplet dynamics on fomites enhances long term bacterial pathogenesis

Naturally drying bacterial droplets on inanimate surfaces representing fomites are the most consequential mode for transmitting infection through oro-fecal route. We provide a multiscale holistic approach to understand flow dynamics induced bacterial pattern formation on fomites leading to pathogenesis. The most virulent gut pathogen, Salmonella Typhimurium (STM), typically found in contaminated food and water, is used as model system in the current study. Evaporation-induced flow in sessile droplets facilitates the transport of STM, forming spatio-temporally varying bacterial deposition patterns based on droplet medium's nutrient scale. Mechanical and low moisture stress in the drying process reduced bacterial viability but interestingly induced hyper-proliferation of STM in macrophages, thereby augmenting virulence in fomites. In vivo studies of fomites in mice confirm that STM maintains enhanced virulence. This work demonstrates that stressed bacterial deposit morphologies formed over small timescale (minutes) on organic and inorganic surfaces, plays a significant role in enhancing fomite's pathogenesis over hours and days.

Cytokine-Mediated Regulation of ARG1 in Macrophages and Its Impact on the Control of Salmonella enterica Serovar Typhimurium Infection

Arginase 1 (ARG1) is a cytosolic enzyme that cleaves L-arginine, the substrate of inducible nitric oxide synthase (iNOS), and thereby impairs the control of various intracellular pathogens. Herein, we investigated the role of ARG1 during infection with Salmonella enterica serovar Typhimurium (S.tm). To study the impact of ARG1 on Salmonella infections in vitro, bone marrow-derived macrophages (BMDM) from C57BL/6N wild-type, ARG1-deficient Tie2Cre+/-ARG1fl/fl and NRAMPG169 C57BL/6N mice were infected with S.tm. In wild-type BMDM, ARG1 was induced by S.tm and further upregulated by the addition of interleukin (IL)-4, whereas interferon-γ had an inhibitory effect. Deletion of ARG1 did not result in a reduction in bacterial numbers. In vivo, Arg1 mRNA was upregulated in the spleen, but not in the liver of C57BL/6N mice following intraperitoneal S.tm infection. The genetic deletion of ARG1 (Tie2Cre+/-ARG1fl/fl) or its pharmacological inhibition with CB-1158 neither affected the numbers of S.tm in spleen, liver and blood nor the expression of host response genes such as iNOS, IL-6 or tumour necrosis factor (TNF). Furthermore, ARG1 was dispensable for pathogen control irrespective of the presence or absence of the phagolysosomal natural resistance-associated macrophage protein 1 (NRAMP1). Thus, unlike the detrimental function of ARG1 seen during infections with other intraphagosomal microorganisms, ARG1 did not support bacterial survival in systemic salmonellosis, indicating differential roles of arginine metabolism for host immune response and microbe persistence depending on the type of pathogen.

Bacteriological and molecular study of Salmonella species associated with central nervous system manifestation in chicken flocks

BACKGROUND AND AIM

Salmonella species often cause systemic health problems in poultry flocks, sometimes including nervous systems manifestations. This impact of Salmonella has rarely been studied. This study aimed to define an alternative pathogenic pathway for Salmonella spp. invasion of brain tissue in chicken flocks. Brain infection produces neurological manifestations; Salmonella strains isolated from brain tissue showed the presences of two virulence genes. Confirmation of the pathway of isolates from intestinal mucosa through the blood-brain barrier was attained using experimental infections in specific pathogen-free (SPF)-day-old chicks through two routes of inoculation.

MATERIALS AND METHODS

Isolation of Salmonella spp. from five chicken flocks that showed signs of the central nervous system (CNS) effects were isolated. Isolates were characterized by serotyping, and antimicrobial assays. In addition, virulence profiles were described using detection of virulence plasmid spvC, and Salmonella plasmid sopB. A pathogenicity study of isolates in specific pathogen-free (SPF)-day-old chicks through oral and intracerebral administration performed, and experimental infection in SPF embryonated chicken eggs through intra-yolk and intra-allantoic administration was investigated. Supporting histopathology and immunohistopathology against Salmonella antigen in brain tissue were performed for flock and experimental infections.

RESULTS

Three serotypes of Salmonella were isolated from the brains of five flocks (two Salmonella Virchow, two Salmonella Kentucky, and one Salmonella Enteritidis isolates). Phage related gene sopB and plasmid-mediated operon spvC were identified in all isolated strains. The Salmonella strains were re-isolated and identified from the brain and internal organs of post-experimental infected chicks. Infected chicks showed nervous manifestations associated with Salmonella infection. The presence of positively stained Salmonella antigen in brain tissues indicates penetration of the blood-brain barrier by the Salmonella species.

CONCLUSION

Our results indicate that some virulent systemic strains of Salmonella spp. can induce CNS manifestations in chicken hosts.

The plasmacytoid dendritic cells evoke Salmonella-specific CTL effector response

Introduction: The immunological role of plasmacytoid dendritic cells (pDC) in bacterial infections such as Salmonella has been poorly documented. Therefore, we analyzed the effector function of these cells by presenting cytotoxic T lymphocytes (CTL) with Salmonella Typhimurium antigens. Objective: To analyze the Salmonella-specific CTL response evoked by pDCs. Materials and methods: We used plasmacytoid dendritic cells stained with carboxyfluorescein succinimidyl ester (CFSE) and pulsed with OmpC73, Salmonella Kb restricted epitopes or S. Typhimurium as targets for cytotoxicity assays. Results: Specific lysis was shown to be statistically significant in pDC + OmpC73 for all effector:target ratios (p≤0.05). For pDC + S. Typhimurium, statistical significance was only observed at a 1:100 ratio (p≤0.05) using OmpC73. Conclusion: Plasmacytoid dendritic cells evoke CTL response during S. Typhimurium infection.

Rapid Isolation of intact Salmonella-containing vacuoles using paramagnetic nanoparticles

Background

Both typhoidal and non-typhoidal Salmonella infections remain a considerable cause of morbidity and mortality globally, and impose a major socio-economic burden worldwide. A key property of all pathogenic Salmonella strains is the ability to invade host cells and reside within an intracellular, vacuolar compartment called the Salmonella-containing vacuole (SCV). Although the SCV is involved in both immune-evasion and intracellular replication and spread within the host, information about the host:pathogen interactions at this interface are limited, in part due to the technical difficulties involved in purification of these vacuoles. While a number of column- or gradient-based methods have been applied, cross-contamination with other host cell organelles or rupture of the labile SCV membrane has further complicated efforts to successfully isolate SCVs.

Results

Here, we report the isolation of intact SCVs using carbon-coated, paramagnetic nanoparticles. The approach permits rapid isolation of intact SCVs from human macrophages in vitro without involving numerous purification steps. Bacteria are pre-labeled with modified nanoparticles prior to infection, and at various times post-infection, host cells are lysed and intact pathogen-containing phagosomes are recovered after application of a mild magnetic field. Purified, intact SCVs isolated using this method were shown to display high levels of co-association of internalized Salmonella with the standard SCV markers Rab5 and LAMP-1 using both microscopic and protein based methods.

Conclusion

The method described is highly efficient, robust and permits rapid isolation of intact SCVs from human macrophages without involving numerous purification steps. The method can also be applied to other intracellular pathogens that reside within a vacuole-like compartment within host cells. Future work using the approach should aid in identification and characterization of host factors associated with the membranes of such intracellular pathogens, which could potentially serve as pharmaceutical targets against intracellular pathogens residing within vacuoles.

Electronic supplementary material

The online version of this article (10.1186/s13099-018-0256-7) contains supplementary material, which is available to authorized users.

Campylobacteriosis, Salmonellosis, Yersiniosis, and Listeriosis as Zoonotic Foodborne Diseases: A Review

Zoonoses are diseases transmitted from animals to humans, posing a great threat to the health and life of people all over the world. According to WHO estimations, 600 million cases of diseases caused by contaminated food were noted in 2010, including almost 350 million caused by pathogenic bacteria. Campylobacter, Salmonella, as well as Yersinia enterocolitica and Listeria monocytogenes may dwell in livestock (poultry, cattle, and swine) but are also found in wild animals, pets, fish, and rodents. Animals, often being asymptomatic carriers of pathogens, excrete them with faeces, thus delivering them to the environment. Therefore, pathogens may invade new individuals, as well as reside on vegetables and fruits. Pathogenic bacteria also penetrate food production areas and may remain there in the form of a biofilm covering the surfaces of machines and equipment. A common occurrence of microbes in food products, as well as their improper or careless processing, leads to common poisonings. Symptoms of foodborne infections may be mild, sometimes flu-like, but they also may be accompanied by severe complications, some even fatal. The aim of the paper is to summarize and provide information on campylobacteriosis, salmonellosis, yersiniosis, and listeriosis and the aetiological factors of those diseases, along with the general characteristics of pathogens, virulence factors, and reservoirs.

Pteris multifida, Cortex phellodendri, and probiotics attenuated inflammatory status and immunity in mice with a Salmonella enterica serovar Typhimurium infection

Pteris multifida (PM) and Cortex phellodendri (CP) are medicinal foods used for gastrointestinal protection. Lactic-acid bacteria are probiotics. Salmonella Typhimurium strain ST21-infected mice were used to examine the alleviative effects of two lactic-acid bacteria (LAB) as well as aqueous extracts of PM and CP for a 4-day treatment. CP and LAB decreased fecal ST counts. CP and PM reduced the ST21 count in the blood, intestine, and liver. LAB lowered the ST21 count in the intestine and spleen. CP and LAB decreased the IFN-gamma level; PM lowered the TNF-alpha level; and both LAB and PM reduced the IL-1beta level in serum. PM and CP lowered the IgG level in serum. The data in a macrophage infection model indicate that TNF-alpha was partial involved in this alleviative effects, other mechanisms might be involved. In sum, these novel findings suggest that PM, CP, and LAB probiotics are potential anti-Salmonellae agents.

Recombinant Salmonella expressing SspH2-EscI fusion protein limits its colonization in mice

Background

Activation of inflammasome contributes to the clearance of intracellular bacteria. C-terminus of E. coli EscI protein can activate NLRC4 (NLR family, CARD domain containing-4) inflammasome in macrophages. The purpose of this study was to determine if activation of NLRC4 inflammasome by EscI can reduce the colonization of Salmonella in mice.

Results

A recombinant S. typhimurium strain expressing fusion protein of the N-terminal SspH2 (a Salmonella type III secretion system 2 effector) and C-terminal EscI was constructed and designated as X4550(pYA3334-SspH2-EscI). In vitro assay showed that X4550(pYA3334-SspH2-EscI) significantly enhanced IL-1β and IL-18 secretion (P < 0.05) and pyroptotic cell death of mouse peritoneal macrophages, compared with those infected with control strain, X4550(pYA3334-SspH2). In vivo studies showed that colonization of X4550(pYA3334-SspH2-EscI) in both spleen and liver were significantly lower than that of X4550(pYA3334-SspH2) (P < 0.05). The bacterial counts of X4550(pYA3334-SspH2-EscI) in mice decreased, while those of X4550(pYA3334-SspH2) increased over the time after infection. Additionally, X4550(pYA3334-SspH2-EscI) induced a less pathological alteration in spleen and liver than X4550(pYA3334-SspH2).

Conclusion

Fusion protein SspH2-EscI may be translocated into macrophages and activate NLRC4 inflammasome, which limits Salmonella colonization in spleen and liver of mice.

Bacterium-Derived Cell-Penetrating Peptides Deliver Gentamicin To Kill Intracellular Pathogens

Commonly used antimicrobials show poor cellular uptake and often have limited access to intracellular targets, resulting in low antimicrobial activity against intracellular pathogens. An efficient delivery system to transport these drugs to the intracellular site of action is needed. Cell-penetrating peptides (CPPs) mediate the internalization of biologically active molecules into the cytoplasm. Here, we characterized two CPPs, α1H and α2H, derived from the Yersinia enterocolitica YopM effector protein. These CPPs, as well as Tat (trans-activator of transcription) from HIV-1, were used to deliver the antibiotic gentamicin to target intracellular bacteria. The YopM-derived CPPs penetrated different endothelial and epithelial cells to the same extent as Tat. CPPs were covalently conjugated to gentamicin, and CPP-gentamicin conjugates were used to target infected cells to kill multiple intracellular Gram-negative pathogenic bacteria, including Escherichia coli K1, Salmonella enterica serovar Typhimurium, and Shigella flexneri Taken together, CPPs show great potential as delivery vehicles for antimicrobial agents and may contribute to the generation of new therapeutic tools to treat infectious diseases caused by intracellular pathogens.

Enhanced intracellular delivery and antibacterial efficacy of enrofloxacin-loaded docosanoic acid solid lipid nanoparticles against intracellular Salmonella

Enrofloxacin-loaded docosanoic acid solid lipid nanoparticles (SLNs) with different physicochemical properties were developed to enhance activity against intracellular Salmonella. Their cellular uptake, intracellular elimination and antibacterial activity were studied in RAW 264.7 cells. During the experimental period, SLN-encapsulated enrofloxacin accumulated in the cells approximately 27.06-37.71 times more efficiently than free drugs at the same extracellular concentration. After incubation for 0.5 h, the intracellular enrofloxacin was enhanced from 0.336 to 1.147 μg/mg of protein as the sizes of nanoparticles were increased from 150 to 605 nm, and from 0.960 to 1.147 μg/mg of protein when the charge was improved from -8.1 to -24.9 mv. The cellular uptake was more significantly influenced by the size than it was by the charge, and was not affected by whether the charge was positive or negative. The elimination of optimal SLN-encapsulated enrofloxacin from the cells was significantly slower than that of free enrofloxacin after removing extracellular drug. The inhibition effect against intracellular Salmonella CVCC541 of 0.24 and 0.06 μg/mL encapsulated enrofloxacin was stronger than 0.6 μg/mL free drug after all of the incubation periods and at 48 h, respectively. Docosanoic acid SLNs are thus considered as a promising carrier for intracellular bacterial treatment.

Role of T3SS-1 SipD Protein in Protecting Mice against Non-typhoidal Salmonella Typhimurium

Background

Salmonella enterica species are enteric pathogens that cause severe diseases ranging from self-limiting gastroenteritis to enteric fever and sepsis in humans. These infectious diseases are still the major cause of morbidity and mortality in low-income countries, especially in children younger than 5 years and immunocompromised adults. Vaccines targeting typhoidal diseases are already marketed, but none protect against non-typhoidal Salmonella. The existence of multiple non-typhoidal Salmonella serotypes as well as emerging antibiotic resistance highlight the need for development of a broad-spectrum protective vaccine. All Salmonella spp. utilize two type III Secretion Systems (T3SS 1 and 2) to initiate infection, allow replication in phagocytic cells and induce systemic disease. T3SS-1, which is essential to invade epithelial cells and cross the barrier, forms an extracellular needle and syringe necessary to inject effector proteins into the host cell. PrgI and SipD form, respectively, the T3SS-1 needle and the tip complex at the top of the needle. Because they are common and highly conserved in all virulent Salmonella spp., they might be ideal candidate antigens for a subunit-based, broad-spectrum vaccine.

Principal Findings

We investigated the immunogenicity and protective efficacy of PrgI and SipD administered by subcutaneous, intranasal and oral routes, alone or combined, in a mouse model of Salmonella intestinal challenge. Robust IgG (in all immunization routes) and IgA (in intranasal and oral immunization routes) antibody responses were induced against both proteins, particularly SipD. Mice orally immunized with SipD alone or SipD combined with PrgI were protected against lethal intestinal challenge with Salmonella Typhimurium (100 Lethal Dose 50%) depending on antigen, route and adjuvant.

Conclusions and Significance

Salmonella T3SS SipD is a promising antigen for the development of a protective Salmonella vaccine, and could be developed for vaccination in tropical endemic areas to control infant mortality.

Salmonella are bacteria responsible for a high global burden of invasive diseases, especially in South and South-East Asia (mainly enteric fever due to Salmonella Typhi) and sub-Saharan Africa (mainly invasive Non-Typhoidal Salmonella, iNTS). This iNTS disease has emerged as a prominent cause of systemic infection in children and immunocompromised African adults, with an associated case fatality of 20–25%. Because licensed vaccines only protect against enteric fever, there is a crucial need to develop a new broad-spectrum vaccine effective against enteric fever and iNTS that can be administered safely to children under 2 years old. The virulence of Salmonella depends on two type III secretion systems (T3SS-1 and T3SS-2) necessary for invasion, replication, intracellular survival and dissemination of the bacteria. Two structural proteins of T3SS-1 (essential for crossing the epithelial barrier) are highly conserved among Salmonella spp. and might be good candidates for a broad-spectrum vaccine. The current study describes the protective effect elicited by these proteins in a murine model. A specific immune response was generated against our antigens and provided protection against Salmonella Typhimurium oral infection. Such a candidate vaccine offers promising perspectives to control Salmonella diseases.

Engineering Salmonella as intracellular factory for effective killing of tumour cells

Salmonella have many desirable properties as antitumour-agent due to its ability to proliferate inside tumours and induce tumour regression. Additionally, this bacterium can be genetically engineered to deliver therapeutic proteins intratumourally. The main limitation of this approach is the efficient release of therapeutic molecules from intratumoural bacteria. Here we have developed an inducible autolysis system based in the lysis operon of the lambda phage that, in response to anhydrotetracycline, lysates Salmonella thus releasing its content. The system was combined with a salicylate cascade system that allows efficient production of therapeutic molecules in response to aspirin and with a sifA mutation that liberates bacteria from the vacuoles to a cytosolic location. The combination of these three elements makes this strain a putative powerful instrument in cancer treatment. We have used this engineered strain for the intracellular production and delivery of Cp53 peptide. The engineered strain is able to sequentially produce and release the cytotoxic peptide while proliferating inside tumour cells, thus inducing host cell death. Our results show that temporal separation of protein production from protein release is essential to efficiently kill tumour cells. The combined system is a further step in the engineering of more efficient bacteria for cancer therapy.

Living with Stress: A Lesson from the Enteric Pathogen Salmonella enterica

The ability to sense and respond to the environment is essential for the survival of all living organisms. Bacterial pathogens such as Salmonella enterica are of particular interest due to their ability to sense and adapt to the diverse range of conditions they encounter, both in vivo and in environmental reservoirs. During this cycling from host to non-host environments, Salmonella encounter a variety of environmental insults ranging from temperature fluctuations, nutrient availability and changes in osmolarity, to the presence of antimicrobial peptides and reactive oxygen/nitrogen species. Such fluctuating conditions impact on various areas of bacterial physiology including virulence, growth and antimicrobial resistance. A key component of the success of any bacterial pathogen is the ability to recognize and mount a suitable response to the discrete chemical and physical stresses elicited by the host. Such responses occur through a coordinated and complex programme of gene expression and protein activity, involving a range of transcriptional regulators, sigma factors and two component regulatory systems. This review briefly outlines the various stresses encountered throughout the Salmonella life cycle and the repertoire of regulatory responses with which Salmonella counters. In particular, how these Gram-negative bacteria are able to alleviate disruption in periplasmic envelope homeostasis through a group of stress responses, known collectively as the Envelope Stress Responses, alongside the mechanisms used to overcome nitrosative stress, will be examined in more detail.

Heme oxygenase 1 controls early innate immune response of macrophages to Salmonella Typhimurium infection

Macrophages are central for the immune control of intracellular microbes. Heme oxygenase 1 (HO-1, hmox) is the first and rate limiting enzyme in the breakdown of heme originating from degraded senescent erythrocytes and heme-proteins, yielding equal amounts of iron, carbon monoxide and biliverdin. HO-1 is strongly up-regulated in macrophages in response to inflammatory signals, including bacterial endotoxin. In view of the essential role of iron for the growth and proliferation of intracellular bacteria along with known effects of the metal on innate immune function, we examined whether HO-1 plays a role in the control of infection with the intracellular bacterium Salmonella Typhimurium. We studied the course of infection in stably-transfected murine macrophages (RAW264.7) bearing a tetracycline-inducible plasmid producing hmox shRNA and in primary HO-1 knockout macrophages. While uptake of bacteria into macrophages was not affected, a significantly reduced survival of intracellular Salmonella was observed upon hmox knockdown or pharmacological hmox inhibition, which was independent of Nramp1 functionality. This could be traced to limitation of iron availability for intramacrophage bacteria along with enhanced stimulation of innate immune effector pathways, including the formation of reactive oxygen and nitrogen species and increased TNF-α expression. Mechanistically, these latter effects result from intracellular iron limitation with subsequent activation of NF-κB and further inos, tnfa and p47phox transcription along with reduced formation of the anti-inflammatory and radical scavenging molecules, CO and biliverdin as a consequence of HO-1 silencing. Taken together our data provide novel evidence that the infection-driven induction of HO-1 exerts detrimental effects in the early control of Salmonella infection, whereas hmox inhibition can favourably modulate anti-bacterial immune effector pathways of macrophages and promote bacterial elimination.

Distocia en una serpiente ratonera amarilla Coelognathus flavolineatus, Schlegel 1837 - Relato de caso

<p>La distocia en reptiles, es una patología caracterizada por la dificultad de llevar a cabo el proceso de parto u ovoposición, la literatura es escasa en lo que concierne a distocias en serpientes, por tanto, existen vacíos frente a este tema. Se describe el caso de una serpiente Coelognathus flavolineatus de 10 años de edad que presentaba dificultad en la ovoposición. Fueron evaluados parámetros sanguíneos, radiográficos y ecográficos, así como cultivo bacteriano y antibiograma, con el fin de identificar las posibles causas y complicaciones que desencadenaron el proceso de distocia en la serpiente. En cuanto al tratamiento de la distocia, se realizó una punción aspirativa del huevo a través de la cloaca, extrayéndose su contenido, posteriormente se procedió a extraer los restos y se tomaron hisopados de la mucosa del tracto reproductivo. Las muestras seleccionadas fueron sometidas a cultivo, donde se aislaron cepas de Salmonella del grupo F-67 y Escherichia coli y en menor proporción cepas de Morganella morganii, Pseudomona aeruginosa, Flavobacterium y Proteus, cuales se atribuyen como agentes infecciosos involucrados en la distocia en la serpiente.</p>

Vigilance for Salmonella in Feedstuffs Available in Costa Rica: Prevalence, Serotyping and Tetracycline Resistance of Isolates Obtained from 2009 to 2014

Relevant epidemiological information is provided in this report for Salmonella based on data obtained from a Costa Rican surveillance program for animal feeds. In addition to prevalence, a description in terms of serotypes and tetracycline (TET) resistance of the isolates is included. A total of 1725 feed and feed ingredients samples were analyzed during 2009 and 2014, from which 110 Salmonella strains were recovered (76 from poultry, 23 from meat and bone meal [MBM], 3 from pet foods, and 8 from other feed). Retrieved isolates were serotyped and tested for minimum inhibitory concentration (MIC) against TET. Salmonella strains were found mainly from poultry feed (different growth stages, n = 76/110; 69.1%) and MBM (n = 23/109; 21.1%). The rest of the isolates were recovered from feather meal, pet food, fish meal (n = 3/110; 2.3% each) and swine feed (n = 1/110; 0.9%). From the different serotypes recovered (n = 21), the most common were Salmonella Give (n = 18; 13.8%) and Salmonella Rissen (n = 6; 4.6%) for MBM and Salmonella Havana (n = 14; 10.8%), Salmonella Rissen, Salmonella Soerenga, and Salmonella Schwarzengrund (n = 8; 6.2% each) in poultry feed. Recovered strains were regarded to be sensitive or have an intermediate resistance to TET as evidenced by their MIC50 and MIC90 concentrations of 4 and 8 μg/mL for MBM and poultry feed, respectively. Compound feed and MBM samples exhibited strains characterized by 86.8 and 88.9% of the isolates classified (according to CLSI, 2015 ) as sensitive, 7.7 and 3.7% as intermediate, and 5.5% (with >256 μg/mL as the highest concentration) and 7.4% (with 64 μg/mL as the highest concentration) as resistant to TET, respectively. Salmonella serovars Anatum and Havana exhibited the highest resistance profile >256 and 128 μg/mL, respectively. Hence, MBM and poultry feed seem to be a target of interest if Salmonella incidence is to be controlled. Serotypes recovered have in the past demonstrated pathogenic capability; therefore, hereafter a stricter surveillance program may be in order.

MdsABC-Mediated Pathway for Pathogenicity in Salmonella enterica Serovar Typhimurium

MdsABC is a Salmonella-specific tripartite efflux pump that has been implicated in the virulence of Salmonella enterica serovar Typhimurium; however, little is known about the virulence factors associated with this pump. We observed MdsABC expression-dependent alterations in the degree of resistance to extracellular oxidative stress and macrophage-mediated killing. Thin-layer chromatography and tandem mass spectrometry analyses revealed that overexpression of MdsABC led to increased secretion of 1-palmitoyl-2-stearoyl-phosphatidylserine (PSPS), affecting the ability of the bacteria to invade and survive in host cells. Overexpression of MdsABC and external addition of PSPS similarly rendered the mdsABC deletion strain resistant to diamide. Diagonal gel analysis showed that PSPS treatment reduced the diamide-mediated formation of disulfide bonds, particularly in the membrane fraction of the bacteria. Salmonella infection of macrophages induced the upregulation of MdsABC expression and led to an increase of intracellular bacterial number and host cell death, similar to the effects of MdsABC overexpression and PSPS pretreatment on the mdsABC deletion strain. Our study shows that MdsABC mediates a previously uncharacterized pathway that involves PSPS as a key factor for the survival and virulence of S. Typhimurium in phagocytic cells.

Coptidis rhizome and Si Jun Zi Tang can prevent Salmonella enterica serovar Typhimurium infection in mice

Salmonella, a common zoonotic pathogen, causes gastroenteritis in both humans and animals. Traditional Chinese Medicine (TCM) has been used to improve gastrointestinal dysfunction and to modify the immune response to inflammation for centuries. This study used six herbal plants and four TCM formulae to rate their efficacy in preventing S. Typhimurium infection via mouse model. Minimum bactericidal concentration (MBC) of Coptidis rhizome (CR) against the reference strain tallied 12.5 mg/ml and against clinical isolate ST21 was 25 mg/ml. MBCs of other herbal extracts and formulae on Salmonella Typhimurium strains were above 50 mg/ml. In the mice model, CR and Si Jun Zi Tang (SJZT) could significantly decrease the bacterial load in organs and blood after being challenged, along with body weight loss due to the infection. CR and SJZT alleviated infection-induced interferon-gamma levels in the serum and tissues, and tumor necrosis factor-alpha (TNF-α) levels in intestinal tissues. CR and SJZT serum metabolites could suppress S. Typhimurium invasion and TNF-α expression in RAW264.7 cells. The therapeutic activity of CR and SJZT may involve berberine, ginsenoside Rb1, and glycyrrhizin, interfering with Salmonella when invading macrophages. CR and SJZT has shown potential in preventing S. Typhimurium infection through the regulation of the immune response.

Responses of macrophages against Salmonella infection compared with phagocytosis

To explore the responses of host cell after infection with live Salmonella compared with phagocytosis to dead bacteria, the responses of mouse macrophage after infection with Salmonella enteritidis C50041 and the fixed C50041 (C50041-d) were analyzed. Results indicated that the cytotoxicity induced by C50041 was stronger than C50041-d. Similar changing trends of mitochondrial membrane potential, intracellular concentration of calcium ions, reactive oxygen species and nitric oxide were found between C50041 and C50041-d infection. But the cell responses against C50041 were earlier and stronger than C50041-d. LC3 expression of macrophage induced by C50041 was lower than C50041-d. C50041 significantly inhibited the production of tumor necrosis factor and interleukin (IL)-6. Whereas intracellular caspase-1 activation and IL-1β release induced by C50041 were stronger than C50041-d, caspase-1 activation and IL-1β release are the innate defense responses of macrophage. Therefore, it will be beneficial to explore the use of this pathway in the control of Salmonella infection.

Salmonella pathogenicity and host adaptation in chicken-associated serovars

Enteric pathogens such as Salmonella enterica cause significant morbidity and mortality. S. enterica serovars are a diverse group of pathogens that have evolved to survive in a wide range of environments and across multiple hosts. S. enterica serovars such as S. Typhi, S. Dublin, and S. Gallinarum have a restricted host range, in which they are typically associated with one or a few host species, while S. Enteritidis and S. Typhimurium have broad host ranges. This review examines how S. enterica has evolved through adaptation to different host environments, especially as related to the chicken host, and continues to be an important human pathogen. Several factors impact host range, and these include the acquisition of genes via horizontal gene transfer with plasmids, transposons, and phages, which can potentially expand host range, and the loss of genes or their function, which would reduce the range of hosts that the organism can infect. S. Gallinarum, with a limited host range, has a large number of pseudogenes in its genome compared to broader-host-range serovars. S. enterica serovars such as S. Kentucky and S. Heidelberg also often have plasmids that may help them colonize poultry more efficiently. The ability to colonize different hosts also involves interactions with the host's immune system and commensal organisms that are present. Thus, the factors that impact the ability of Salmonella to colonize a particular host species, such as chickens, are complex and multifactorial, involving the host, the pathogen, and extrinsic pressures. It is the interplay of these factors which leads to the differences in host ranges that we observe today.

Interaction of silver nanoparticles with serum proteins affects their antimicrobial activity in vivo

The emergence of multidrug-resistant bacteria is a global threat for human society. There exist recorded data that silver was used as an antimicrobial agent by the ancient Greeks and Romans during the 8th century. Silver nanoparticles (AgNPs) are of potential interest because of their effective antibacterial and antiviral activities, with minimal cytotoxic effects on the cells. However, very few reports have shown the usage of AgNPs for antibacterial therapy in vivo. In this study, we deciphered the importance of the chosen methods for synthesis and capping of AgNPs for their improved activity in vivo. The interaction of AgNPs with serum albumin has a significant effect on their antibacterial activity. It was observed that uncapped AgNPs exhibited no antibacterial activity in the presence of serum proteins, due to the interaction with bovine serum albumin (BSA), which was confirmed by UV-Vis spectroscopy. However, capped AgNPs [with citrate or poly(vinylpyrrolidone)] exhibited antibacterial properties due to minimized interactions with serum proteins. The damage in the bacterial membrane was assessed by flow cytometry, which also showed that only capped AgNPs exhibited antibacterial properties, even in the presence of BSA. In order to understand the in vivo relevance of the antibacterial activities of different AgNPs, a murine salmonellosis model was used. It was conclusively proved that AgNPs capped with citrate or PVP exhibited significant antibacterial activities in vivo against Salmonella infection compared to uncapped AgNPs. These results clearly demonstrate the importance of capping agents and the synthesis method for AgNPs in their use as antimicrobial agents for therapeutic purposes.

Antagonistic activity of Lactobacillus acidophilus LA10 against Salmonella enterica serovar Enteritidis SE86 in mice

Salmonella enterica serovar Enteritidis is one of the main pathogens responsible for foodborne illness in Brazil. Probiotic bacteria can play a role in defense and recovery from enteropathogenic infections. In this study, the ability of Lactobacillus acidophilus LA10 to colonise and exert antagonistic effects in the gastrointestinal tract was tested before and during experimental infection in conventional mice contaminated with S. Enteritidis (SE86). A dose of 0.1 mL containing 10⁸ viable cells of SE86 and L. acidophilus LA10 was orally administered by gavage to mice. The experiment was divided into groups. As a negative control, Group 1 was administered only sterile saline solution. As a positive control, Group 2 was administered only SE86. Group 3 was first administered SE86, and after 10 days, treated with L. acidophilus LA10. Group 4 was first administered L. acidophilus LA10, and after 10 days, challenged with SE86. The results demonstrated that a significant number of SE86 cells were able to colonize the gastrointestinal tract of mice, specifically in the colon and ileum. L. acidophilus LA10 demonstrated an antagonistic effect against SE86, with better results observed for Group 3 over Group 4. Thus, L. acidophilus LA10 shows potential antagonistic effects against S. Enteritidis SE86, especially if administered after infection.

Salmonella enterica serovars Typhimurium and Typhi as model organisms: revealing paradigm of host-pathogen interactions

The lifestyle of intracellular pathogens has always questioned the skill of a microbiologist in the context of finding the permanent cure to the diseases caused by them. The best tool utilized by these pathogens is their ability to reside inside the host cell, which enables them to easily bypass the humoral immunity of the host, such as the complement system. They further escape from the intracellular immunity, such as lysosome and inflammasome, mostly by forming a protective vacuole-bound niche derived from the host itself. Some of the most dreadful diseases are caused by these vacuolar pathogens, for example, tuberculosis by Mycobacterium or typhoid fever by Salmonella. To deal with such successful pathogens therapeutically, the knowledge of a host-pathogen interaction system becomes primarily essential, which further depends on the use of a model system. A well characterized pathogen, namely Salmonella, suits the role of a model for this purpose, which can infect a wide array of hosts causing a variety of diseases. This review focuses on various such aspects of research on Salmonella which are useful for studying the pathogenesis of other intracellular pathogens.

Nanomedicine as an emerging approach against intracellular pathogens

Diseases such as tuberculosis, hepatitis, and HIV/AIDS are caused by intracellular pathogens and are a major burden to the global medical community. Conventional treatments for these diseases typically consist of long-term therapy with a combination of drugs, which may lead to side effects and contribute to low patient compliance. The pathogens reside within intracellular compartments of the cell, which provide additional barriers to effective treatment. Therefore, there is a need for improved and more effective therapies for such intracellular diseases. This review will summarize, for the first time, the intracellular compartments in which pathogens can reside and discuss how nanomedicine has the potential to improve intracellular disease therapy by offering properties such as targeting, sustained drug release, and drug delivery to the pathogen’s intracellular location. The characteristics of nanomedicine may prove advantageous in developing improved or alternative therapies for intracellular diseases.

Nifedipine affects the course of Salmonella enterica serovar Typhimurium infection by modulating macrophage iron homeostasis

BACKGROUND

Iron overload can adversely influence the course of infection by increasing microbial replication and suppressing antimicrobial immune effector pathways. Recently, we have shown that the calcium channel blocker nifedipine can mobilize tissue iron in mouse models of iron overload. We therefore investigated whether nifedipine treatment affects the course of infection with intracellular bacteria via modulation of iron homeostasis.

METHODS

The effect of nifedipine on intramacrophage replication of bacteria and modulation of cellular iron homeostasis was investigated in the murine macrophage cell line RAW264.7, and the impact of nifedipine treatment on the course of systemic infection was investigated in C57BL/6 mice in vivo.

RESULTS

In RAW264.7 cells, nifedipine treatment significantly reduced intracellular bacterial survival of Salmonella enterica serovar Typhimurium and Chlamydophila pneumoniae. This could be attributed to the induction of the iron exporter ferroportin 1, which limited the availability of iron for intracellular Salmonella. When C57BL/6 mice were infected intraperitoneally with Salmonella and subsequently injected with nifedipine for 3 consecutive days, bacterial counts in livers and spleens were significantly reduced and survival of the mice significantly was prolonged compared with solvent-treated littermates. Nifedipine treatment increased expression of ferroportin 1 in the spleen, whereas splenic levels of the iron storage protein ferritin and serum iron concentrations were reduced.

CONCLUSIONS

Our data provide evidence for a novel mechanism whereby nifedipine enhances host resistance to intracellular pathogens via limitation of iron availability.

Small-molecular virulence inhibitors show divergent and immunomodulatory effects in infection models of Salmonella enterica serovar Typhimurium

The virulence-associated Salmonella pathogenicity island 2 (SPI2) type III secretion system supports intracellular replication of Salmonella enterica serovar Typhimurium in macrophage-like RAW264.7 cells. In contrast, the salicylidene acylhydrazide INP0010 and the benzimidazole omeprazole prevent virulence factor-mediated replication of S. Typhimurium in these cells. Here we show that INP0010 enhances expression of inducible nitric oxide synthase (iNOS), nitric oxide (NO) production, the oxidative burst and tumour necrosis factor-alpha (TNFα) release in infected RAW264.7 cells. INP0010 also inhibited SPI2 activity in RAW264.7 cells. The ability of INP0010 to suppress bacterial intracellular replication correlated with NO production. The iNOS inhibitor N-monomethyl-l-arginine restored SPI2 activity and antagonised the bacteriostatic effect of INP0010. Omeprazole, which inhibited iNOS expression in RAW264.7 cells, likewise antagonised INP0010. In infected epithelioid MDCK cells that did not express NO upon infection, INP0010 enhanced bacterial intracellular replication. In Caenorhabditis elegans, INP0010 significantly attenuated the virulence of S. Typhimurium. In this infection model, the attenuating effect of INP0010 was further enhanced by omeprazole. These results demonstrate that chemically unrelated virulence inhibitors may act in an antagonistic or additive manner, that their effect depends on the infection model applied, and that the attenuating effects of INP0010 in part relate to its ability to promote the SPI2 antagonist NO.

Biofilm formation by Salmonella enterica serovar Typhimurium colonizing solid tumours

Systemic administration of Salmonella enterica serovar Typhimurium to tumour bearing mice results in preferential colonization of the tumours and retardation of tumour growth. Although the bacteria are able to invade the tumour cells in vitro, in tumours they were never detected intracellularly. Ultrastructural analysis of Salmonella-colonized tumours revealed that the bacteria had formed biofilms. Interestingly, depletion of neutrophilic granulocytes drastically reduced biofilm formation. Obviously, bacteria form biofilms in response to the immune reactions of the host. Importantly, we tested Salmonella mutants that were no longer able to form biofilms by deleting central regulators of biofilm formation. Such bacteria could be observed intracellularly in immune cells of the host or in tumour cells. Thus, tumour colonizing S. typhimurium might form biofilms as protection against phagocytosis. Since other bacteria are behaving similarly, solid murine tumours might represent a unique model to study biofilm formation in vivo.

TolA mediates the differential detergent resistance pattern between the Salmonella enterica subsp. enterica serovars Typhi and Typhimurium

The tol-pal genes are essential for maintaining the outer membrane integrity and detergent resistance in various Gram-negative bacteria, including Salmonella. The role of TolA has been well established for the bile resistance of Salmonella enterica subsp. enterica serovar Typhimurium. We compared the bile resistance pattern between the S. enterica serovars Typhi and Typhimurium and observed that Typhi is more resistant to bile-mediated damage. A closer look revealed a significant difference in the TolA sequence between the two serovars which contributes to the differential detergent resistance. The tolA knockout of both the serovars behaves completely differently in terms of membrane organization and morphology. The role of the Pal proteins and difference in LPS organization between the two serovars were verified and were found to have no direct connection with the altered bile resistance. In normal Luria broth (LB), S. Typhi ΔtolA is filamentous while S. Typhimurium ΔtolA grows as single cells, similar to the wild-type. In low osmolarity LB, however, S. Typhimurium ΔtolA started chaining and S. Typhi ΔtolA showed no growth. Further investigation revealed that the chaining phenomenon observed was the result of failure of the outer membrane to separate in the dividing cells. Taken together, the results substantiate the evolution of a shorter TolA in S. Typhi to counteract high bile concentrations, at the cost of lower osmotic tolerance.

Spread of Salmonella enterica in the body during systemic infection: unravelling host and pathogen determinants

Salmonella enterica causes a range of life-threatening diseases in humans and animals worldwide. Current treatments for S. enterica infections are not sufficiently effective, and there is a need to develop new vaccines and therapeutics. An understanding of how S. enterica spreads in tissues has very important implications for targeting bacteria with vaccine-induced immune responses and antimicrobial drugs. Development of new control strategies would benefit from a more sophisticated evaluation of bacterial location, spatiotemporal patterns of spread and distribution in the tissues, and sites of microbial persistence. We review here recent studies of S. enterica serovar Typhimurium (S. Typhimurium) infections in mice, an established model of systemic typhoid fever in humans, which suggest that continuous bacterial spread to new infection foci and host phagocytes is an essential trait in the virulence of S. enterica during systemic infections. We further highlight how infections within host tissues are truly heterogeneous processes despite the fact that they are caused by the expansion of a genetically homogeneous microbial population. We conclude by discussing how understanding the within-host quantitative, spatial and temporal dynamics of S. enterica infections might aid the development of novel targeted preventative measures and drug regimens.