How does the oxidative burst of macrophages kill bacteria? Still an open question

In Silico Model of Vitamin D3 Dependent NADPH Oxidase Complex Activation During Mycobacterium Infection

Mycobacterium tuberculosis (Mtb) is a highly infectious aerosolizable bacterium, which causes upward of 1.5 million deaths per year. Alveolar macrophages, the primary defense cell of the lung, are the preferred host cell of this intracellular bacterium. Vitamin D₃ is a known transcription factor, modulating the transcription of pro- and anti-inflammatory cytokines and immunologically relevant proteins. In a vitamin D₃ deficient host, the immune systems response to infection is greatly impaired. We used a quantitative systems biology approach to model the impact of long-term vitamin D₃ deficiency on macrophage effector response. We then compared our simulation output to our in vitro model of mycobacterium infection of macrophages from vitamin D₃ supplemented hosts. Our in silico model results agreed with in vitro levels of hydrogen peroxide (H₂O₂) production, an antimicrobial effector molecule produced by the host's macrophage, known to be modulated indirectly by vitamin D₃. The current model will provide a foundation for further studies into the effects of micronutrient deficiency on immune response.

Phagosomal Copper-Promoted Oxidative Attack on Intracellular Mycobacterium tuberculosis

Copper (Cu) ions are critical in controlling bacterial infections, and successful pathogens like Mycobacterium tuberculosis (Mtb) possess multiple Cu resistance mechanisms. We report, as proof of concept, that a novel Cu hypersensitivity phenotype can be generated in mycobacteria, including Mtb, through a peptide, DAB-10, that is able to form reactive oxygen species (ROS) following Cu-binding. DAB-10 induces intramycobacterial oxidative stress in a Cu-dependent manner in vitro and during infection. DAB-10 penetrates murine macrophages and encounters intracellular mycobacteria. Significant intracellular Cu-dependent protection was observed when Mtb-infected macrophages were treated with DAB-10 alongside a cell-permeable Cu chelator. Treatment with the Cu chelator reversed the intramycobacterial oxidative shift induced by DAB-10. We conclude that DAB-10 utilizes the pool of phagosomal Cu ions in the host-Mtb interface to augment the mycobactericidal activity of macrophages while simultaneously exploiting the susceptibility of Mtb to ROS. DAB-10 serves as a model with which to develop next-generation, multifunctional antimicrobials.

A Mutation in the Mesorhizobium loti oatB Gene Alters the Physicochemical Properties of the Bacterial Cell Wall and Reduces Survival inside Acanthamoeba castellanii

In our previous report, we had shown that the free-living amoeba Acanthamoeba castellanii influenced the abundance, competiveness, and virulence of Mesorhizobium loti NZP2213, the microsymbiont of agriculturally important plants of the genus Lotus. The molecular basis of this phenomenon; however, had not been explored. In the present study, we demonstrated that oatB, the O-acetyltransferase encoding gene located in the lipopolysaccharide (LPS) synthesis cluster of M. loti, was responsible for maintaining the protective capacity of the bacterial cell envelope, necessary for the bacteria to fight environmental stress and survive inside amoeba cells. Using co-culture assays combined with fluorescence and electron microscopy, we showed that an oatB mutant, unlike the parental strain, was efficiently destroyed after rapid internalization by amoebae. Sensitivity and permeability studies of the oatB mutant, together with topography and nanomechanical investigations with the use of atomic force microscopy (AFM), indicated that the incomplete substitution of lipid A-core moieties with O-polysaccharide (O-PS) residues rendered the mutant more sensitive to hydrophobic compounds. Likewise, the truncated LPS moieties, rather than the lack of O-acetyl groups, made the oatB mutant susceptible to the bactericidal mechanisms (nitrosative stress and the action of lytic enzymes) of A. castellanii.

Immunomodulatory effect of Cynara scolymus (artichoke) in rats

Cynara scolymus is a plant used both as food as well as medicinal plant worldwide. Cynarin is one of the main active principles of the plant, and it is also present in species such as Echinacea purpurae, which is known to have immunomodulatory activity. Thus, the objective of this study is to evaluate the immune effects of C. scolymus in rats. Rats were treated with 1.0-, 2.0-, or 4.0-g/kg body weight of C. scolymus extract for 28 days. Haemogram, serum biochemistry, lymphoid organs weight, and their cell phenotypes were evaluated. Macrophages and neutrophils oxidative burst, specific humoral immune response, and the delayed-type hypersensitivity (DTH) were studied. No changes in the haemogram, biochemical profile, antibody titers, lymphoid organs, and in their cellularities were observed. An increase in the basal activity of reactive oxygen species from male's macrophage was observed. There was a suppression of the DTH response in both gender when treated with the highest dose of C. scolymus. This study is the first in the literature that revealed an immunosuppressive effect of C. scolymus. We also verified that the doses of artichoke extract here employed did not cause general toxicity.

Oxeiptosis: a discreet way to respond to radicals

One of the best-studied cellular responses to toxic signals and pathogens is programmed cell death. Over the past years, it became apparent that the specific mechanisms of cell death have tremendous influence at both cellular and organismal level, highlighting the importance of sensors and pathways involved in this decision-making process. Central signalling molecules involved in a variety of cell death pathways are reactive oxygen species (ROS). However, the molecular mechanisms regulating differential responses and cellular fates to distinct ROS levels remain incompletely understood. Recently, we uncovered a caspase-independent cell-death pathway named 'oxeiptosis', which links the ROS sensing capacity of KEAP1 to a cell death pathway involving PGAM5 and AIFM1. Alike apoptosis, oxeiptosis is anti-inflammatory when activated by increased intracellular ROS levels and upon pathogens encounter. Here we discuss the potential impact of oxeiptosis in pathogens clearance and teratogenic cells.

Compromised DNA Repair and Signalling in Human Granulocytes

In previous studies, we showed impaired DNA repair in human monocytes. Here, we addressed the question of whether human neutrophilic granulocytes that arise from the same precursor as monocytes exhibit a similar phenotype and are impaired in repairing their DNA. We show that neutrophilic granulocytes isolated from peripheral blood display a lack of the same repair proteins that are missing in monocytes and do not show repair of their DNA when damaged by ionising radiation (IR) or chemical ROS. Contrary to T cells, we observed no decline in the number of single-strand breaks following γ-radiation. Also, granulocytes did not show γH2AX foci formation while T cells and peripheral blood lymphocytes (PBL) responded. In comparison to PBL, XRCC1, PARP-1 and ligase III were not expressed and there was also no discernible signal for key damage response proteins ATM, ATR and DNA-PKCS as well as γH2AX in neutrophils. Time course and dose-response experiments confirmed the absence of H2AX phosphorylation after radiation treatment although an accumulation of double-strand breaks was detected in the neutral Comet assay. Overall, the data indicate that terminally differentiated neutrophilic granulocytes in the peripheral blood display strong downregulation of DNA repair and DNA damage response factors, which should be taken into account if studies with whole peripheral blood containing granulocytes are performed, causing a significant intra-experimental variation in the cellular repair capacity.

Inflammatory production of reactive oxygen species by Drosophila hemocytes activates cellular immune defenses

The production of reactive oxygen species (ROS) is a prominent response to infection among innate immune cells such as macrophages and neutrophils. To better understand the relationship between antimicrobial and regulatory functions of blood cell ROS, we have characterized the ROS response to infection in Drosophila hemocytes. Using fluorescent probes, we find a biphasic hemocyte ROS response to bacterial infection. In the first hour, virtually all hemocytes generate a transient ROS signal, with nonphagocytic cells including prohemocytes and crystal cells displaying exceptionally strong responses. A distinct, and more delayed ROS response starting at 90 min is primarily within cells that have engulfed bacteria, and is sustained for several hours. The early response has a clear regulatory function, as dampening or intensifying the intracellular ROS level has profound effects on plasmatocyte activation. In addition, ROS are necessary and sufficient to activate JNK signalling in crystal cells, and to promote JNK-dependent crystal cell rupture. These findings indicate that Drosophila will be a promising model in which to dissect the mechanisms of ROS stimulation of immune activation.

Perforin-2 Breaches the Envelope of Phagocytosed Bacteria Allowing Antimicrobial Effectors Access to Intracellular Targets

Perforin-2, the product of the MPEG1 gene, limits the spread and dissemination of bacterial pathogens in vivo. It is highly expressed in murine and human phagocytes, and macrophages lacking Perforin-2 are compromised in their ability to kill phagocytosed bacteria. In this study, we used Salmonella enterica serovar Typhimurium as a model intracellular pathogen to elucidate the mechanism of Perforin-2's bactericidal activity. In vitro Perforin-2 was found to facilitate the degradation of Ags contained within the envelope of phagocytosed bacteria. In contrast, degradation of a representative surface Ag was found to be independent of Perforin-2. Consistent with our in vitro results, a protease-sensitive, periplasmic superoxide dismutase (SodCII) contributed to the virulence of S. Typhimurium in Perforin-2 knockout but not wild-type mice. In aggregate, our studies indicate that Perforin-2 breaches the envelope of phagocytosed bacteria, facilitating the delivery of proteases and other antimicrobial effectors to sites within the bacterial cell.

Taurodeoxycholate Increases the Number of Myeloid-Derived Suppressor Cells That Ameliorate Sepsis in Mice

Bile acids (BAs) control metabolism and inflammation by interacting with several receptors. Here, we report that intravenous infusion of taurodeoxycholate (TDCA) decreases serum pro-inflammatory cytokines, normalizes hypotension, protects against renal injury, and prolongs mouse survival during sepsis. TDCA increases the number of granulocytic myeloid-derived suppressor cells (MDSCLT) distinctive from MDSCs obtained without TDCA treatment (MDSCL) in the spleen of septic mice. FACS-sorted MDSCLT cells suppress T-cell proliferation and confer protection against sepsis when adoptively transferred better than MDSCL. Proteogenomic analysis indicated that TDCA controls chromatin silencing, alternative splicing, and translation of the immune proteome of MDSCLT, which increases the expression of anti-inflammatory molecules such as oncostatin, lactoferrin and CD244. TDCA also decreases the expression of pro-inflammatory molecules such as neutrophil elastase. These findings suggest that TDCA globally edits the proteome to increase the number of MDSCLT cells and affect their immune-regulatory functions to resolve systemic inflammation during sepsis.

The ArcAB two-component regulatory system promotes resistance to reactive oxygen species and systemic infection by Salmonella Typhimurium

Salmonella enterica Serovar Typhimurium (S. Typhimurium) is an intracellular bacterium that overcomes host immune system barriers for successful infection. The bacterium colonizes the proximal small intestine, penetrates the epithelial layer, and is engulfed by macrophages and neutrophils. Intracellularly, S. Typhimurium encounters highly toxic reactive oxygen species including hydrogen peroxide and hypochlorous acid. The molecular mechanisms of Salmonella resistance to intracellular oxidative stress is not completely understood. The ArcAB two-component system is a global regulatory system that responds to oxygen. In this work, we show that the ArcA response regulator participates in Salmonella adaptation to changing oxygen levels and is also involved in promoting intracellular survival in macrophages and neutrophils, enabling S. Typhimurium to successfully establish a systemic infection.

Redox imbalance contributed differently to membrane damage of cucumber leaves under water stress and Fusarium infection

Redox-associated events are important in plant development and responses to environmental stresses. In this study, we investigated spatial redox responses of cucumber (Cucumis sativus L.) leaves to biotic stress (Fusarium infection) or abiotic stress (water stress). Plants were grown under hydroponic conditions and either treated with polyethylene glycol to simulate drought or infected with Fusarium oxysporum f. sp. cucumerinum. Both water stress and Fusarium infection restricted cucumber growth and were associated with cellular plasma-membrane damage, reactive oxygen species accumulation, and changes in antioxidants; however, the responses to each stress were distinctive. Under water stress, H₂O₂ generation at the leaf edge increased 29.7% compared with that at the centre but with Fusarium infection there was a relative 10.4% decrease at the edge. These changes correlated with changes in antioxidants and linked enzyme activities. The key sources of variation in oxidative events were defined by principal component analysis of all of the data and redox balance evaluations. We suggest that these spatial differences under water stress and Fusarium infection arise from discrete regulatory mechanisms, reflecting either developmental effect over the leaf regions or systemic anti-oxidative events occurred following infection.

Effect of anti-retroviral therapy on oxidative stress in hospitalized HIV-infected adults with and without TB

Background

HIV infection and opportunistic infections cause oxidative stress (OS), which is associated with tissue damage. Anti-retroviral therapy (ART) is used to treat HIV and decrease the risk of opportunistic infections, but it is unclear whether ART reduces OS. Association of ART with OS was investigated.

Methods

We stratified a convenience sample of frozen serum or plasma from HIV-infected, ART-naïve (n=21); HIV-infected, ART-treated (n=14); HIV and PTB co-infected, ART-naïve (n=21); HIV and PTB co-infected, ART-treated (n=25) patients. Controls (n=21) were HIV-negative adults without TB symptoms. Concentration of OS markers namely: transaminases (ALT and AST), gamma glutamyl transpeptidase (GGT), albumin, total protein, malondialdehyde (MDA), vitamin C, and total anti-oxidant status (TAS) were determined.

Results

AST (p<0.001), GGT (p<0.001), total protein (p=0.001) and MDA (p<0.001) were higher in HIV patients compared to controls. Vitamin C (P<0.0001) and albumin (p<0.01) were lower in HIV-patients relative to controls. ART was only associated with higher albumin (p=0.001), higher GGT (p=0.02) and lower vitamin C (p=0.009). HIV and PTB co-infection was only significantly associated with higher GGT (p=0.01) and AST (p=0.03).

Conclusion

We identified severe OS among HIV-patients. ART was associated with both increased and reduced markers of OS hence suggesting that ART may not attenuate OS.

NADPH Oxidase and Guanylate Binding Protein 5 Restrict Survival of Avirulent Type III Strains of Toxoplasma gondii in Naive Macrophages

Toxoplasma infections in humans and other mammals are largely controlled by IFN-γ produced by the activated adaptive immune system. However, we still do not completely understand the role of cell-intrinsic functions in controlling Toxoplasma or other apicomplexan infections. The present work identifies intrinsic activities in naive macrophages in counteracting T. gondii infection. Using an avirulent strain of T. gondii, we highlight the importance of Nox complexes in conferring protection against parasite infection both in vitro and in vivo. We also identify Gbp5 as a novel macrophage factor involved in limiting intracellular infection by avirulent strains of T. gondii. The rarity of human infections caused by type III strains suggests that these mechanisms may also be important in controlling human toxoplasmosis. These findings further extend our understanding of host responses and defense mechanisms that act to control parasitic infections at the cellular level.

Phagocytic cells are the first line of innate defense against intracellular pathogens, and yet Toxoplasma gondii is renowned for its ability to survive in macrophages, although this paradigm is based on virulent type I parasites. Surprisingly, we find that avirulent type III parasites are preferentially cleared in naive macrophages, independent of gamma interferon (IFN-γ) activation. The ability of naive macrophages to clear type III parasites was dependent on enhanced activity of NADPH oxidase (Nox)-generated reactive oxygen species (ROS) and induction of guanylate binding protein 5 (Gbp5). Macrophages infected with type III parasites (CTG strain) showed a time-dependent increase in intracellular ROS generation that was higher than that induced by type I parasites (GT1 strain). The absence of Nox1 or Nox2, gp91 subunit isoforms of the Nox complex, reversed ROS-mediated clearance of CTG parasites. Consistent with this finding, both Nox1^−/− and Nox2^−/− mice showed higher susceptibility to CTG infection than wild-type mice. Additionally, Gbp5 expression was induced upon infection and the enhanced clearance of CTG strain parasites was reversed in Gbp5^−/− macrophages. Expression of a type I ROP18 allele in CTG prevented clearance in naive macrophages, suggesting that it plays a role counteracting Gbp5. Although ROS and Gbp5 have been linked to activation of the NLRP3 inflammasome, clearance of CTG parasites did not rely on induction of pyroptosis. Collectively, these findings reveal that not all strains of T. gondii are adept at avoiding clearance in macrophages and define new roles for ROS and Gbps in controlling this important intracellular pathogen.

LDL dinitrosyl iron complex acts as an iron donor in mouse macrophages

[Fe(NO)₂] - modified nanoparticles of low-density protein (DNICLDL) can serve as conveyors of iron in the form of stable complexes with ApoB100 protein. As reported recently, in human hepatoma cells DNICLDL significantly increased the total iron content, while showing low toxicity. In the present work, we focused on the effects of internalization of DNIC-modified lipoproteins in macrophages, with special regards to cytotoxicity. DNICLDL was administered to a model macrophage cell line, RAW 264.7. Administration of DNICLDL considerably increased total iron content. High increase of iron was accompanied by moderate toxicity. As shown by in vitro plasmid nicking assay, chelation of iron in the form of DNIC strongly reduced the iron-related reactive oxygen species (ROS) -induced DNA damage. In addition, DNICLDL, plausibly due to its NO-donating activity, did not induce inducible nitric oxide synthase (iNOS) expression, as opposed to other forms of low-density protein (LDL).

Chemical Warfare at the Microorganismal Level: A Closer Look at the Superoxide Dismutase Enzymes of Pathogens

Superoxide anion radical is generated as a natural byproduct of aerobic metabolism but is also produced as part of the oxidative burst of the innate immune response design to kill pathogens. In living systems, superoxide is largely managed through superoxide dismutases (SODs), families of metalloenzymes that use Fe, Mn, Ni, or Cu cofactors to catalyze the disproportionation of superoxide to oxygen and hydrogen peroxide. Given the bursts of superoxide faced by microbial pathogens, it comes as no surprise that SOD enzymes play important roles in microbial survival and virulence. Interestingly, microbial SOD enzymes not only detoxify host superoxide but also may participate in signaling pathways that involve reactive oxygen species derived from the microbe itself, particularly in the case of eukaryotic pathogens. In this Review, we will discuss the chemistry of superoxide radicals and the role of diverse SOD metalloenzymes in bacterial, fungal, and protozoan pathogens. We will highlight the unique features of microbial SOD enzymes that have evolved to accommodate the harsh lifestyle at the host-pathogen interface. Lastly, we will discuss key non-SOD superoxide scavengers that specific pathogens employ for defense against host superoxide.

mTORC2 Activity Disrupts Lysosome Acidification in Systemic Lupus Erythematosus by Impairing Caspase-1 Cleavage of Rab39a

Lysosomes maintain immune homeostasis through the degradation of phagocytosed apoptotic debris; however, the signaling events regulating lysosomal maturation remain undefined. In this study, we show that lysosome acidification, key to the maturation process, relies on mTOR complex 2 (mTORC2), activation of caspase-1, and cleavage of Rab39a. Mechanistically, the localization of cofilin to the phagosome recruits caspase-11, which results in the localized activation of caspase-1. Caspase-1 subsequently cleaves Rab39a on the phagosomal membrane, promoting lysosome acidification. Although caspase-1 is critical for lysosome acidification, its activation is independent of inflammasomes and cell death mediated by apoptosis-associated speck-like protein containing a caspase recruitment domain, revealing a role beyond pyroptosis. In lupus-prone murine macrophages, chronic mTORC2 activity decouples the signaling pathway, leaving Rab39a intact. As a result, the lysosome does not acidify, and degradation is impaired, thereby heightening the burden of immune complexes that activate FcγRI and sustain mTORC2 activity. This feedforward loop promotes chronic immune activation, leading to multiple lupus-associated pathologies. In summary, these findings identify the key molecules in a previously unappreciated signaling pathway that promote lysosome acidification. It also shows that this pathway is disrupted in systemic lupus erythematosus.

Biochemistry of proinflammatory macrophage activation

In the last decade, metabolism has been recognized as a major determinant of immunological processes. During an inflammatory response, macrophages undergo striking changes in their metabolism. This metabolic reprogramming is governed by a complex interplay between metabolic enzymes and metabolites of different pathways and represents the basis for proper macrophage function. It is now evident that these changes go far beyond the well-known Warburg effect and the perturbation of metabolic targets is being investigated as a means to treat infections and auto-immune diseases. In the present review, we will aim to provide an overview of the metabolic responses during proinflammatory macrophage activation and show how these changes modulate the immune response.

Quantification of Bioorthogonal Stability in Immune Phagocytes Using Flow Cytometry Reveals Rapid Degradation of Strained Alkynes

One of the areas in which bioorthogonal chemistry—chemistry performed inside a cell or organism—has become of pivotal importance is in the study of host–pathogen interactions. The incorporation of bioorthogonal groups into the cell wall or proteome of intracellular pathogens has allowed study within the endolysosomal system. However, for the approach to be successful, the incorporated bioorthogonal groups must be stable to chemical conditions found within these organelles, which are some of the harshest found in metazoans: the groups are exposed to oxidizing species, acidic conditions, and reactive thiols. Here we present an assay that allows the assessment of the stability of bioorthogonal groups within host cell phagosomes. Using a flow cytometry-based assay, we have quantified the relative label stability inside dendritic cell phagosomes of strained and unstrained alkynes. We show that groups that were shown to be stable in other systems were degraded by as much as 79% after maturation of the phagosome.

ROS and Trypanosoma cruzi: Fuel to infection, poison to the heart

The activation of macrophage respiratory burst in response to infection with Trypanosoma cruzi inflicts oxidative damage to the host’s tissues. For decades, the role of reactive oxygen species (ROS) in the elimination of T. cruzi was taken for granted, but recent evidence suggests parasite growth is stimulated in oxidative environments. It is still a matter of debate whether indeed oxidative environments provide ideal conditions (e.g., iron availability in macrophages) for T. cruzi growth and whether indeed ROS signals directly to stimulate growth. Nitric oxide (NO) and ROS combine to form peroxynitrite, participating in the killing of phagocytosed parasites by activated macrophages. In response to infection, mitochondrial ROS are produced by cardiomyocytes. They contribute to oxidative damage that persists at the chronic stage of infection and is involved in functional impairment of the heart. In this review, we discuss how oxidative stress helps parasite growth during the acute stage and how it participates in the development of cardiomyopathy at the chronic stage.

Crosstalk Between Sphingomyelinases and Reactive Oxygen Species in Mycobacterial Infection

Significance: Tuberculosis (TB), which is caused by Mycobacterium tuberculosis, is one of the most important infections worldwide. The sphingomyelinase/ceramide system, which has been shown to be a crucial factor in internalizing and killing various pathogens, modulates both the proinflammatory response and the state of mycobacteria in macrophages. However, studies about the role of sphingomyelinases in TB are still at an early stage. Recent Advances: Recent studies elucidated several roles of sphingomyelinases in manipulating mycobacterial infections. On the one hand, acid sphingomyelinase (Asm) promotes the fusion of bacteria-containing phagosomes and lysosomes, whereas on the other hand, Asm-derived ceramide induces cell death. Neutral sphingomyelinase (Nsm) enhances the release of reactive oxygen species, which suppress autophagy in infected macrophages in vitro and in vivo, allowing the pathogen to survive within macrophages. These findings indicate that the sphingomyelinase/ceramide system plays an important role in the attack of mycobacteria against the host. Critical Issues: Autophagy is a main strategy of mycobacterial clearance in TB, but the relevant mechanisms are still unknown. Additionally, there are indications that both Asm and Nsm are crucially involved in the formation of granulomas, which are a hallmark and a special structure of TB. However, very few findings have yet been published. Future Directions: Additional studies of the Nsm/ceramide system, which contributes to the resistance or susceptibility, respectively, of the host to mycobacterial infections, will detect currently unknown molecular mechanisms. Because inhibitors of Nsm already exist, targeting Nsm may be a novel approach to developing treatment options for mycobacterial infections. Antioxid. Redox Signal. 28, 935-948.

HIV and the Macrophage: From Cell Reservoirs to Drug Delivery to Viral Eradication

Macrophages serve as host cells, inflammatory disease drivers and drug runners for human immunodeficiency virus infection and treatments. Low-level viral persistence continues in these cells in the absence of macrophage death. However, the cellular microenvironment changes as a consequence of viral infection with aberrant production of pro-inflammatory factors and promotion of oxidative stress. These herald viral spread from macrophages to neighboring CD4⁺ T cells and end organ damage. Virus replicates in tissue reservoir sites that include the nervous, pulmonary, cardiovascular, gut, and renal organs. However, each of these events are held in check by antiretroviral therapy. A hidden and often overlooked resource of the macrophage rests in its high cytoplasmic nuclear ratios that allow the cell to sense its environment and rid it of the cellular waste products and microbial pathogens it encounters. These phagocytic and intracellular killing sensing mechanisms can also be used in service as macrophages serve as cellular carriage depots for antiretroviral nanoparticles and are able to deliver medicines to infectious disease sites with improved therapeutic outcomes. These undiscovered cellular functions can lead to reductions in persistent infection and may potentially facilitate the eradication of residual virus to eliminate disease.

Conversion of RpoS- Attenuated Salmonella enterica Serovar Typhi Vaccine Strains to RpoS+ Improves Their Resistance to Host Defense Barriers

Recombinant attenuated Salmonella vaccines (RASVs) represent a unique prevention strategy to combating infectious disease because they utilize the ability of Salmonella to invade and colonize deep effector lymphoid tissues and deliver hetero- and homologous derived antigens at the lowest immunizing dose. Our recent clinical trial in human volunteers indicated that an RpoS⁺ derivative of Ty2 was better at inducing immune responses than its RpoS⁻ counterpart. In this study, we demonstrate that a functional RpoS allele is beneficial for developing effective live attenuated vaccines against S. Typhi or in using S. Typhi as a recombinant attenuated vaccine vector to deliver other protective antigens.

The vast majority of live attenuated typhoid vaccines are constructed from the Salmonella enterica serovar Typhi strain Ty2, which is devoid of a functioning alternative sigma factor, RpoS, due to the presence of a frameshift mutation. RpoS is a specialized sigma factor that plays an important role in the general stress response of a number of Gram-negative organisms, including Salmonella. Previous studies have demonstrated that this sigma factor is necessary for survival following exposure to acid, hydrogen peroxide, nutrient-limiting conditions, and starvation. In addition, studies with Salmonella enterica serovar Typhimurium and the mouse model of typhoid fever have shown that RpoS is important in colonization and survival within the infected murine host. We converted 4 clinically studied candidate typhoid vaccine strains derived from Ty2 [CVD908-htrA, Ty800, and χ9639(pYA3493)] and the licensed live typhoid vaccine Ty21a (also derived from Ty2) to RpoS⁺ and compared their abilities to withstand environmental stresses that may be encountered within the host to those of the RpoS⁻ parent strains. The results of our study indicate that strains that contain a functional RpoS were better able to survive following stress and that they would be ideal for further development as safe, effective vaccines to prevent S. Typhi infections or as vectors in recombinant attenuated Salmonella vaccines (RASVs) designed to protect against other infectious disease agents in humans. The S. Typhi strains constructed and described here will be made freely available upon request, as will the suicide vector used to convert rpoS mutants to RpoS⁺.

IMPORTANCE Recombinant attenuated Salmonella vaccines (RASVs) represent a unique prevention strategy to combating infectious disease because they utilize the ability of Salmonella to invade and colonize deep effector lymphoid tissues and deliver hetero- and homologous derived antigens at the lowest immunizing dose. Our recent clinical trial in human volunteers indicated that an RpoS⁺ derivative of Ty2 was better at inducing immune responses than its RpoS⁻ counterpart. In this study, we demonstrate that a functional RpoS allele is beneficial for developing effective live attenuated vaccines against S. Typhi or in using S. Typhi as a recombinant attenuated vaccine vector to deliver other protective antigens.

Biological macromolecules based targeted nanodrug delivery systems for the treatment of intracellular infections

Intracellular infections are tricky to treat, the reason being the poor penetration of antibiotics/antimycotics into the microbial niche (host cell). Macrophages are primary targets of facultative and obligate intracellular bacteria/fungi to be abused as host cells. The need for drugs with better intracellular penetration led to the development of endocytosable drug carriers, which can cross the cell membrane of the host cells (macrophages) by imitating the entry path of the pathogens. Therefore, the drugs can be targeted to macrophages ensuring enhanced therapeutic effect. This review discusses the exploitation of various nanocarriers for targeted delivery of drugs to the macrophages in the last two decades.

Melatonin inhibits apoptotic cell death induced by Vibrio vulnificus VvhA via melatonin receptor 2 coupling with NCF-1

Melatonin, an endogenous hormone molecule, has a variety of biological functions, but a functional role of melatonin in the infection of Gram-negative bacterium Vibrio vulnificus has yet to be described. In this study, we investigated the molecular mechanism of melatonin in the apoptosis of human intestinal epithelial (HCT116) cells induced by the hemolysin (VvhA) produced by V. vulnificus. Melatonin (1 μM) significantly inhibited apoptosis induced by the recombinant protein (r) VvhA, which had been inhibited by the knockdown of MT₂. The rVvhA recruited caveolin-1, NCF-1, and Rac1 into lipid rafts to facilitate the production of ROS responsible for the phosphorylation of PKC and JNK. Interestingly, melatonin recruited NCF-1 into non-lipid rafts to prevent ROS production via MT₂ coupling with Gαq. Melatonin inhibited the JNK-mediated phosphorylation of c-Jun responsible for Bax expression, the release of mitochondrial cytochrome c, and caspase-3/-9 activation during its promotion of rVvhA-induced apoptotic cell death. In addition, melatonin inhibited JNK-mediated phosphorylation of Bcl-2 responsible for the release of Beclin-1 and Atg5 expression during its promotion of rVvhA-induced autophagic cell death. These results demonstrate that melatonin signaling via MT₂ triggers recruitment of NCF-1 into non-lipid rafts to block ROS production and JNK-mediated apoptotic and autophagic cell deaths induced by rVvhA in intestinal epithelial cells.

Macrophage Bactericidal Assays

The search for the bactericidal activity of macrophage (Mϕ) is crucial not only during infection, but also to explore its functional activities in normal and pathological conditions, such as autoimmune and inflammatory disorders, allergic inflammation, and cancer. There are several methods exploring the phagocytic and bactericidal activities of Mϕ. This chapter focuses specifically on the technique called antibiotic protection assay and on the methods for the determination of Mϕ production of nitric oxide and hydrogen peroxide as antimicrobial agents and biomarkers of respiratory burst. The protocols presented herein are valid for both Mϕ cell lines and monocyte-derived Mϕs (MDMs).

A Comprehensive Assessment of the Genetic Determinants in Salmonella Typhimurium for Resistance to Hydrogen Peroxide Using Proteogenomics

Salmonella is an intracellular pathogen infecting a wide range of hosts and can survive in macrophages. An essential mechanism used by macrophages to eradicate Salmonella is production of reactive oxygen species. Here, we used proteogenomics to determine the candidate genes and proteins that have a role in resistance of S. Typhimurium to H₂O₂. For Tn-seq, a saturated Tn5 insertion library was grown in vitro under either 2.5 (H₂O₂L) or 3.5 mM H₂O₂ (H₂O₂H). We identified two sets of overlapping genes required for resistance of S. Typhimurium to H₂O₂L and H₂O₂H, and the results were validated via phenotypic evaluation of 50 selected mutants. The enriched pathways for H₂O₂ resistance included DNA repair, aromatic amino acid biosynthesis (aroBK), Fe-S cluster biosynthesis, iron homeostasis and a putative iron transporter system (ybbKLM), and H₂O₂ scavenging enzymes. Proteomics revealed that the majority of essential proteins, including ribosomal proteins, were downregulated upon exposure to H₂O₂. On the contrary, a subset of conditionally essential proteins identified by Tn-seq were analyzed by targeted proteomics, and 70% of them were upregulated by H₂O₂. The identified genes will deepen our understanding on S. Typhimurium survival mechanisms in macrophages, and can be exploited to develop new antimicrobial drugs.

Immune response against rickettsiae: lessons from murine infection models

Rickettsiae are small intracellular bacteria that can cause life-threatening febrile diseases. Rickettsioses occur worldwide with increasing incidence. Therefore, a vaccine is highly desired. A prerequisite for the development of a vaccine is the knowledge of the immune response against these bacteria, in particular protective immunity. In recent years murine models of rickettsial infections have been established, and the study of immune response against rickettsiae in mice provided many new insights into protective and pathological immune reactions. This review summarizes the current knowledge about immune mechanisms in protection and pathology in rickettsial infections.

Black, White, and Gray: Macrophages in Skin Repair and Disease

PURPOSE OF REVIEW

Macrophages alter their responses during the temporal stages of wound healing. During the inflammatory phase macrophages perform phagocytosis. During neovascularization macrophages activate angiogenesis. In the proliferation phase of wound healing, macrophages deposit extracellular matrix and during wound resolution macrophages phagocytize excessive cellular components. This review addresses how these changing phenotypes affect skin repair and disease.

RECENT FINDINGS

Macrophages can determine the outcome of repair and can shift the normal wound healing response into fibrosis or chronic wounds. Emerging single cell technologies for the first time provide us with tools to uncover macrophage origin, heterogeneity and function.

SUMMARY

Macrophages may exist as one population where all cells alter their phenotype in response to signals from the microenvironment. Alternatively, macrophages may exist as distinct subsets that can control wound outcomes. A clarified understanding will strengthen our knowledge of skin biology and aid in the development of wound healing therapies.

Macrophage-Microbe Interactions: Lessons from the Zebrafish Model

Macrophages provide front line defense against infections. The study of macrophage-microbe interplay is thus crucial for understanding pathogenesis and infection control. Zebrafish (Danio rerio) larvae provide a unique platform to study macrophage-microbe interactions in vivo, from the level of the single cell to the whole organism. Studies using zebrafish allow non-invasive, real-time visualization of macrophage recruitment and phagocytosis. Furthermore, the chemical and genetic tractability of zebrafish has been central to decipher the complex role of macrophages during infection. Here, we discuss the latest developments using zebrafish models of bacterial and fungal infection. We also review novel aspects of macrophage biology revealed by zebrafish, which can potentiate development of new therapeutic strategies for humans.

Cytoplasmic Copper Detoxification in Salmonella Can Contribute to SodC Metalation but Is Dispensable during Systemic Infection

Salmonella enterica serovar Typhimurium is a leading cause of foodborne disease worldwide. Severe infections result from the ability of S Typhimurium to survive within host immune cells, despite being exposed to various host antimicrobial factors. SodCI, a copper-zinc-cofactored superoxide dismutase, is required to defend against phagocytic superoxide. SodCII, an additional periplasmic superoxide dismutase, although produced during infection, does not function in the host. Previous studies suggested that CueP, a periplasmic copper binding protein, facilitates acquisition of copper by SodCII. CopA and GolT, both inner membrane ATPases that pump copper from the cytoplasm to the periplasm, are a source of copper for CueP. Using in vitro SOD assays, we found that SodCI can also utilize CueP to acquire copper. However, both SodCI and SodCII have a significant fraction of activity independent of CueP and cytoplasmic copper export. We utilized a series of mouse competition assays to address the in vivo role of CueP-mediated SodC activation. A copA golT cueP triple mutant was equally as competitive as the wild type, suggesting that sufficient SodCI is active to defend against phagocytic superoxide independent of CueP and cytoplasmic copper export. We also confirmed that a strain containing a modified SodCII, which is capable of complementing a sodCI deletion, was fully virulent in a copA golT cueP background competed against the wild type. These competitions also address the potential impact of cytoplasmic copper toxicity within the phagosome. Our data suggest that Salmonella does not encounter inhibitory concentrations of copper during systemic infection.IMPORTANCESalmonella is a leading cause of gastrointestinal disease worldwide. In severe cases, Salmonella can cause life-threatening systemic infections, particularly in very young children, the elderly, or people who are immunocompromised. To cause disease, Salmonella must survive the hostile environment inside host immune cells, a location in which most bacteria are killed. Our work examines how one particular metal, copper, is acquired by Salmonella to activate a protein important for survival within immune cells. At high levels, copper itself can inhibit Salmonella Using a strain of Salmonella that cannot detoxify intracellular copper, we also addressed the in vivo role of copper as an antimicrobial agent.

Synthetic Peptides to Target Stringent Response-Controlled Virulence in a Pseudomonas aeruginosa Murine Cutaneous Infection Model

Microorganisms continuously monitor their surroundings and adaptively respond to environmental cues. One way to cope with various stress-related situations is through the activation of the stringent stress response pathway. In Pseudomonas aeruginosa this pathway is controlled and coordinated by the activity of the RelA and SpoT enzymes that metabolize the small nucleotide secondary messenger molecule (p)ppGpp. Intracellular ppGpp concentrations are crucial in mediating adaptive responses and virulence. Targeting this cellular stress response has recently been the focus of an alternative approach to fight antibiotic resistant bacteria. Here, we examined the role of the stringent response in the virulence of P. aeruginosa PAO1 and the Liverpool epidemic strain LESB58. A ΔrelA/ΔspoT double mutant showed decreased cytotoxicity toward human epithelial cells, exhibited reduced hemolytic activity, and caused down-regulation of the expression of the alkaline protease aprA gene in stringent response mutants grown on blood agar plates. Promoter fusions of relA or spoT to a bioluminescence reporter gene revealed that both genes were expressed during the formation of cutaneous abscesses in mice. Intriguingly, virulence was attenuated in vivo by the ΔrelA/ΔspoT double mutant, but not the relA mutant nor the ΔrelA/ΔspoT complemented with either gene. Treatment of a cutaneous P. aeruginosa PAO1 infection with anti-biofilm peptides increased animal welfare, decreased dermonecrotic lesion sizes, and reduced bacterial numbers recovered from abscesses, resembling the phenotype of the ΔrelA/ΔspoT infection. It was previously demonstrated by our lab that ppGpp could be targeted by synthetic peptides; here we demonstrated that spoT promoter activity was suppressed during cutaneous abscess formation by treatment with peptides DJK-5 and 1018, and that a peptide-treated relA complemented stringent response double mutant strain exhibited reduced peptide susceptibility. Overall these data strongly indicated that synthetic peptides target the P. aeruginosa stringent response in vivo and thus offer a promising novel therapeutic approach.

LC3-Associated Phagocytosis and Inflammation

LC3-associated phagocytosis (LAP) is a novel form of non-canonical autophagy where LC3 (microtubule-associated protein 1A/1B-light chain 3) is conjugated to phagosome membranes using a portion of the canonical autophagy machinery. The impact of LAP to immune regulation is best characterized in professional phagocytes, in particular macrophages, where LAP has instrumental roles in the clearance of extracellular particles including apoptotic cells and pathogens. Binding of dead cells via receptors present on the macrophage surface results in the translocation of the autophagy machinery to the phagosome and ultimately LC3 conjugation. These events promote a rapid form of phagocytosis that produces an "immunologically silent" clearance of the apoptotic cells. Consequences of LAP deficiency include a decreased capacity to clear dying cells and the establishment of a lupus-like autoimmune disease in mice. The ability of LAP to attenuate autoimmunity likely occurs through the dampening of pro-inflammatory signals upon engulfment of dying cells and prevention of autoantigen presentation to other immune cells. However, it remains unclear how LAP shapes both the activation and outcome of the immune response at the molecular level. Herein, we provide a detailed review of LAP and its known roles in the immune response and provide further speculation on the putative mechanisms by which LAP may regulate immune function, perhaps through the metabolic reprogramming and polarization of macrophages.

Intracellular Salmonella metabolism

Growth of Salmonella inside infected host cells is a key aspect of their ability to cause local enteritis or systemic disease. This growth depends on exploitation of host nutrients through a large Salmonella metabolism network with hundreds of metabolites and enzymes. Studies in cell culture infection models are unravelling more and more of the underlying molecular and cellular mechanisms but also show striking Salmonella metabolic plasticity depending on host cell line and experimental conditions. In vivo studies have revealed a qualitatively diverse, but quantitatively poor, host-Salmonella nutritional interface, which on one side makes Salmonella fitness largely resilient against metabolic perturbations, but on the other side severely limits Salmonella biomass generation and growth rates. This review discusses goals and techniques for studying Salmonella intracellular metabolism, summarises main results and implications, and proposes key issues that could be addressed in future studies.

Crystal structure of Yersinia pestis virulence factor YfeA reveals two polyspecific metal-binding sites

Gram-negative bacteria use siderophores, outer membrane receptors, inner membrane transporters and substrate-binding proteins (SBPs) to transport transition metals through the periplasm. The SBPs share a similar protein fold that has undergone significant structural evolution to communicate with a variety of differentially regulated transporters in the cell. In Yersinia pestis, the causative agent of plague, YfeA (YPO2439, y1897), an SBP, is important for full virulence during mammalian infection. To better understand the role of YfeA in infection, crystal structures were determined under several environmental conditions with respect to transition-metal levels. Energy-dispersive X-ray spectroscopy and anomalous X-ray scattering data show that YfeA is polyspecific and can alter its substrate specificity. In minimal-media experiments, YfeA crystals grown after iron supplementation showed a threefold increase in iron fluorescence emission over the iron fluorescence emission from YfeA crystals grown from nutrient-rich conditions, and YfeA crystals grown after manganese supplementation during overexpression showed a fivefold increase in manganese fluorescence emission over the manganese fluorescence emission from YfeA crystals grown from nutrient-rich conditions. In all experiments, the YfeA crystals produced the strongest fluorescence emission from zinc and could not be manipulated otherwise. Additionally, this report documents the discovery of a novel surface metal-binding site that prefers to chelate zinc but can also bind manganese. Flexibility across YfeA crystal forms in three loops and a helix near the buried metal-binding site suggest that a structural rearrangement is required for metal loading and unloading.

Oxidative stress induced in E. coli by the human antimicrobial peptide LL-37

Antimicrobial peptides (AMPs) are thought to kill bacterial cells by permeabilizing their membranes. However, some antimicrobial peptides inhibit E. coli growth more efficiently in aerobic than in anaerobic conditions. In the attack of the human cathelicidin LL-37 on E. coli, real-time, single-cell fluorescence imaging reveals the timing of membrane permeabilization and the onset of oxidative stress. For cells growing aerobically, a CellROX Green assay indicates that LL-37 induces rapid formation of oxidative species after entry into the periplasm, but before permeabilization of the cytoplasmic membrane (CM). A cytoplasmic Amplex Red assay signals a subsequent burst of oxidative species, most likely hydrogen peroxide, shortly after permeabilization of the CM. These signals are much stronger in the presence of oxygen, a functional electron transport chain, and a large proton motive force (PMF). They are much weaker in cells growing anaerobically, by either fermentation or anaerobic respiration. In aerobic growth, the oxidative signals are attenuated in a cytochrome oxidase–bd deletion mutant, but not in a –bo₃ deletion mutant, suggesting a specific effect of LL-37 on the electron transport chain. The AMPs melittin and LL-37 induce strong oxidative signals and exhibit O₂-sensitive MICs, while the AMPs indolicidin and cecropin A do not. These results suggest that AMP activity in different tissues may be tuned according to the local oxygen level. This may be significant for control of opportunistic pathogens while enabling growth of commensal bacteria.

Antimicrobial peptides play a significant role in the innate immune response of plants and animals, including humans. While it is well known that AMPs can permeabilize bacterial cell membranes, a growing body of evidence indicates that they cause a variety of additional deleterious effects. Here we use single-cell imaging methods to study the induction of oxidative stress in live E. coli by several natural cationic AMPs, including the human cathelicidin LL-37. Strong fluorescence signals indicative of oxidative stress correlate with smaller minimum inhibitory concentrations (MICs) in aerobic vs anaerobic growth conditions. A detailed mechanistic study suggests that LL-37 disrupts the proper flow of electrons through the electron transport chain, releasing oxidative species into the periplasm. Based on these results, we suggest that the degree of aeration in different tissue types may be used by the host to modulate AMP efficacy.

OhrR of Mycobacterium smegmatis senses and responds to intracellular organic hydroperoxide stress

Organic hydroperoxide reductase regulator (OhrR) in bacteria is a sensor for organic hydroperoxide stress and a transcriptional regulator for the enzyme organic hydroperoxide reductase (Ohr). In this study we investigated, using a GFP reporter system, whether Mycobacterium smegmatis OhrR has the ability to sense and respond to intracellular organic hydroperoxide stress. It was observed that M. smegmatis strains bearing the pohr-gfpuv fusion construct were able to express GFP only in the absence of an intact ohrR gene, but not in its presence. However, GFP expression in the strain bearing pohr-gfpuv with an intact ohrR gene could be induced by organic hydroperoxides in vitro and in the intracellular environment upon ingestion of the bacteria by macrophages; indicating that OhrR responds not only to in vitro but also to intracellular organic hydroperoxide stress. Further, the intracellular expression of pohr driven GFP in this strain could be abolished by replacing the intact ohrR gene with a mutant ohrR gene modified for N-terminal Cysteine (Cys) residue, suggesting that OhrR senses intracellular organic hydroperoxides through Cys residue. This is the first report demonstrating the ability of OhrR to sense intracellular organic hydroperoxides.

Systematic in vitro assessment of responses of roGFP2-based probes to physiologically relevant oxidant species

The genetically encoded probes roGFP2-Orp1 and Grx1-roGFP2 have been designed to be selectively oxidized by hydrogen peroxide (H₂O₂) and glutathione disulfide (GSSG), respectively. Both probes have demonstrated such selectivity in a broad variety of systems and conditions. In this study, we systematically compared the in vitro response of roGFP2, roGFP2-Orp1 and Grx1-roGFP2 to increasing amounts of various oxidant species that may also occur in biological settings. We conclude that the previously established oxidant selectivity is highly robust and likely to be maintained under most physiological conditions. Yet, we also find that hypochlorous acid, known to be produced in the phagocyte respiratory burst, can lead to non-selective oxidation of roGFP2-based probes at concentrations ≥2µM, in vitro. Further, we confirm that polysulfides trigger direct roGFP2 responses. A side-by-side comparison of all three probes can be used to reveal micromolar amounts of hypochlorous acid or polysulfides.

The lack of BTK does not impair monocytes and polymorphonuclear cells functions in X-linked agammaglobulinemia under treatment with intravenous immunoglobulin replacement

The lack of BTK in X-linked agammaglobulinemia (XLA) patients does not affect monocytes and polymorphonuclear cells (PMN) phenotype and functions. In this study, we show that XLA patients had an increased frequency of the intermediate monocytes subset and that BTK-deficient monocytes and PMN had a normal expression of receptors involved in the activation and cellular responses. We demonstrate that BTK is not required for migration, phagocytosis and the production of reactive oxygen species (ROS) following engagement of FC gamma receptors (FcγR). XLA monocytes and PMN showed an efficient calcium (Ca2+)-independent activation of oxidative burst, suggesting that oxidative burst is less dependent by Ca2+ mobilization. The phagocytosis was functional and it remained unaltered also after Ca2+ chelation, confirming the independence of phagocytosis on Ca2+ mobilization. Intravenous immunoglobulin (IVIg) infusion exerted an anti-inflammatory effect by reducing the frequency of pro-inflammatory monocytes. In monocytes, the IVIg reduce the oxidative burst and phagocytosis even if these functions remained efficient.

New iminodibenzyl derivatives with anti-leishmanial activity

Leishmaniasis is an infection caused by protozoa of the genus Leishmania and transmitted by sandflies. Current treatments are expensive and time-consuming, involving Sb(V)-based compounds, lipossomal amphotericin B and miltefosine. Recent studies suggest that inhibition of trypanothione reductase (TR) could be a specific target in the development of new drugs because it is essential and exclusive to trypanosomatids. This work presents the synthesis and characterization of new iminodibenzyl derivatives (dado) with ethylenediamine (ea), ethanolamine (en) and diethylenetriamine (dien) and their copper(II) complexes. Computational methods indicated that the complexes were highly lipophilic. Pro-oxidant activity assays by oxidation of the dihydrorhodamine (DHR) fluorimetric probe showed that [Cu(dado-ea)]²⁺ has the highest rate of oxidation, independent of H₂O₂ concentration. The toxicity to L. amazonensis promastigotes and RAW 264,7 macrophages was assessed, showing that dado-en was the most active new compound. Complexation to copper did not have an appreciable effect on the toxicity of the compounds.

Copper and Antibiotics: Discovery, Modes of Action, and Opportunities for Medicinal Applications

Copper is a ubiquitous element in the environment as well as living organisms, with its redox capabilities and complexation potential making it indispensable for many cellular functions. However, these same properties can be highly detrimental to prokaryotes and eukaryotes when not properly controlled, damaging many biomolecules including DNA, lipids, and proteins. To restrict free copper concentrations, all bacteria have developed mechanisms of resistance, sequestering and effluxing labile copper to minimize its deleterious effects. This weakness is actively exploited by phagocytes, which utilize a copper burst to destroy pathogens. Though administration of free copper is an unreasonable therapeutic antimicrobial itself, due to insufficient selectivity between host and pathogen, small-molecule ligands may provide an opportunity for therapeutic mimicry of the immune system. By modulating cellular entry, complex stability, resistance evasion, and target selectivity, ligand/metal coordination complexes can synergistically result in high levels of antibacterial activity. Several established therapeutic drugs, such as disulfiram and pyrithione, display remarkable copper-dependent inhibitory activity. These findings have led to development of new drug discovery techniques, using copper ions as the focal point. High-throughput screens for copper-dependent inhibitors against Mycobacterium tuberculosis and Staphylococcus aureus uncovered several new compounds, including a new class of inhibitors, the NNSNs. In this review, we highlight the microbial biology of copper, its antibacterial activities, and mechanisms to discover new inhibitors that synergize with copper.

Cytotoxic effector functions of T cells are not required for protective immunity against fatal Rickettsia typhi infection in a murine model of infection: Role of TH1 and TH17 cytokines in protection and pathology

Endemic typhus caused by Rickettsia (R.) typhi is an emerging febrile disease that can be fatal due to multiple organ pathology. Here we analyzed the requirements for protection against R. typhi by T cells in the CB17 SCID model of infection. BALB/c wild-type mice generate CD4+ TH1 and cytotoxic CD8+ T cells both of which are sporadically reactivated in persistent infection. Either adoptively transferred CD8+ or CD4+ T cells protected R. typhi-infected CB17 SCID mice from death and provided long-term control. CD8+ T cells lacking either IFNγ or Perforin were still protective, demonstrating that the cytotoxic function of CD8+ T cells is not essential for protection. Immune wild-type CD4+ T cells produced high amounts of IFNγ, induced the release of nitric oxide in R. typhi-infected macrophages and inhibited bacterial growth in vitro via IFNγ and TNFα. However, adoptive transfer of CD4+IFNγ-/- T cells still protected 30-90% of R. typhi-infected CB17 SCID mice. These cells acquired a TH17 phenotype, producing high amounts of IL-17A and IL-22 in addition to TNFα, and inhibited bacterial growth in vitro. Surprisingly, the neutralization of either TNFα or IL-17A in CD4+IFNγ-/- T cell recipient mice did not alter bacterial elimination by these cells in vivo, led to faster recovery and enhanced survival compared to isotype-treated animals. Thus, collectively these data show that although CD4+ TH1 cells are clearly efficient in protection against R. typhi, CD4+ TH17 cells are similarly protective if the harmful effects of combined production of TNFα and IL-17A can be inhibited.

Laribacter hongkongensis anaerobic adaptation mediated by arginine metabolism is controlled by the cooperation of FNR and ArgR

Laribacter hongkongensis is a fish-borne pathogen associated with invasive infections and gastroenteritis. Its adaptive mechanisms to oxygen-limiting conditions in various environmental niches remain unclear. In this study, we compared the transcriptional profiles of L. hongkongensis under aerobic and anaerobic conditions using RNA-sequencing. Expression of genes involved in arginine metabolism significantly increased under anoxic conditions. Arginine was exploited as the sole energy source in L. hongkongensis for anaerobic respiration via the arginine catabolism pathway: specifically via the arginine deiminase (ADI) pathway. A transcriptional regulator FNR was identified to coordinate anaerobic metabolism by tightly regulating the expression of arginine metabolism genes. FNR executed its regulatory function by binding to FNR boxes in arc operons promoters. Survival of isogenic fnr mutant in macrophages decreased significantly when compared with wild-type; and expression level of fnr increased 8 h post-infection. Remarkably, FNR directly interacted with ArgR, another regulator that influences the biological fitness and intracellular survival of L. hongkongensis by regulating arginine metabolism genes. Our results demonstrated that FNR and ArgR work in coordination to respond to oxygen changes in both extracellular and intracellular environments, by finely regulating the ADI pathway and arginine anabolism pathways, thereby optimizing bacterial fitness in various environmental niches.

The Role of Reactive Oxygen Species in Adipogenic Differentiation

Interest in reactive oxygen species and adipocyte differentiation/adipose tissue function is steadily increasing. This is due in part to a search for alternative avenues for combating obesity, which results from the excess accumulation of adipose tissue. Obesity is a major risk factor for complex disorders such as cancer, type 2 diabetes, and cardiovascular diseases. The ability of mesenchymal stromal/stem cells (MSCs) to differentiate into adipocytes is often used as a model for studying adipogenesis in vitro. A key focus is the effect of both intra- and extracellular reactive oxygen species (ROS) on adipogenesis. The consensus from the majority of studies is that ROS, irrespective of the source, promote adipogenesis.The effect of ROS on adipogenesis is suppressed by antioxidants or ROS scavengers. Reactive oxygen species are generated during the process of adipocyte differentiation as well as by other cell metabolic processes. Despite many studies in this field, it is still not possible to state with certainty whether ROS measured during adipocyte differentiation are a cause or consequence of this process. In addition, it is still unclear what the exact sources are of the ROS that initiate and/or drive adipogenic differentiation in MSCs in vivo. This review provides an overview of our understanding of the role of ROS in adipocyte differentiation as well as how certain ROS scavengers and antioxidants might affect this process.

Eradication of Pseudomonas aeruginosa biofilms and persister cells using an electrochemical scaffold and enhanced antibiotic susceptibility

Biofilms in chronic wounds are known to contain a persister subpopulation that exhibits enhanced multidrug tolerance and can quickly rebound after therapeutic treatment. The presence of these “persister cells” is partly responsible for the failure of antibiotic therapies and incomplete elimination of biofilms. Electrochemical methods combined with antibiotics have been suggested as an effective alternative for biofilm and persister cell elimination, yet the mechanism of action for improved antibiotic efficacy remains unclear. In this work, an electrochemical scaffold (e-scaffold) that electrochemically generates a constant concentration of H₂O₂ was investigated as a means of enhancing tobramycin susceptibility in pre-grown Pseudomonas aeruginosa PAO1 biofilms and attacking persister cells. Results showed that the e-scaffold enhanced tobramycin susceptibility in P. aeruginosa PAO1 biofilms, which reached a maximum susceptibility at 40 µg/ml tobramycin, with complete elimination (7.8-log reduction vs control biofilm cells, P ≤ 0.001). Moreover, the e-scaffold eradicated persister cells in biofilms, leaving no viable cells (5-log reduction vs control persister cells, P ≤ 0.001). It was observed that the e-scaffold induced the intracellular formation of hydroxyl free radicals and improved membrane permeability in e-scaffold treated biofilm cells, which possibly enhanced antibiotic susceptibility and eradicated persister cells. These results demonstrate a promising advantage of the e-scaffold in the treatment of persistent biofilm infections.

Using an electrically conductive fabric to generate hydrogen peroxide could eradicate persistent biofilms in chronically infected wounds. Electrochemical scaffolds (e-scaffolds) are thin networks of conductive material such as carbon fiber used to generate chemical responses in media they are in contact with. Haluk Beyenal and colleagues at Washington State University, USA, investigated the effect of a carbon fabric e-scaffold on cultured biofilms of the bacterium Pseudomonas aeruginosa. The procedure enhanced the susceptibility of this troublesome multidrug-resistant bacterium to the antibiotic tobramycin. Crucially, it eradicated so-called persister cells that can evade antibiotic treatment to reform biofilms in chronic wounds. The research suggests that the effect involves the production of hydroxyl free radicals from hydrogen peroxide and increased permeability of the bacterial cell membranes. The potential of e-scaffolds for treating infected wounds warrants further exploration.

Oxidative and nitrosative stress defences of Helicobacter and Campylobacter species that counteract mammalian immunity

Helicobacter and Campylobacter species are Gram-negative microaerophilic host-associated heterotrophic bacteria that invade the digestive tract of humans and animals. Campylobacter jejuni is the major worldwide cause of foodborne gastroenteritis in humans, while Helicobacter pylori is ubiquitous in over half of the world's population causing gastric and duodenal ulcers. The colonisation of the gastrointestinal system by Helicobacter and Campylobacter relies on numerous cellular defences to sense the host environment and respond to adverse conditions, including those imposed by the host immunity. An important antimicrobial tool of the mammalian innate immune system is the generation of harmful oxidative and nitrosative stresses to which pathogens are exposed during phagocytosis. This review summarises the regulators, detoxifying enzymes and subversion mechanisms of Helicobacter and Campylobacter that ultimately promote the successful infection of humans.

Chemical and Stress Resistances of Clostridium difficile Spores and Vegetative Cells

Clostridium difficile is a Gram-positive, sporogenic and anaerobic bacterium that causes a potentially fatal colitis. C. difficile enters the body as dormant spores that germinate in the colon to form vegetative cells that secrete toxins and cause the symptoms of infection. During transit through the intestine, some vegetative cells transform into spores, which are more resistant to killing by environmental insults than the vegetative cells. Understanding the inherent resistance properties of the vegetative and spore forms of C. difficile is imperative for the development of methods to target and destroy the bacterium. The objective of this study was to define the chemical and environmental resistance properties of C. difficile vegetative cells and spores. We examined vegetative cell and spore tolerances of three C. difficile strains, including 630Δerm, a 012 ribotype and a derivative of a past epidemic strain; R20291, a 027 ribotype and current epidemic strain; and 5325, a clinical isolate that is a 078 ribotype. All isolates were tested for tolerance to ethanol, oxygen, hydrogen peroxide, butanol, chloroform, heat and sodium hypochlorite (household bleach). Our results indicate that 630Δerm vegetative cells (630 spo0A) are more resistant to oxidative stress than those of R20291 (R20291 spo0A) and 5325 (5325 spo0A). In addition, 5325 spo0A vegetative cells exhibited greater resistance to organic solvents. In contrast, 630Δerm spores were more sensitive than R20291 or 5325 spores to butanol. Spores from all three strains exhibited high levels of resistance to ethanol, hydrogen peroxide, chloroform and heat, although R20291 spores were more resistant to temperatures in the range of 60-75°C. Finally, household bleach served as the only chemical reagent tested that consistently reduced C. difficile vegetative cells and spores of all tested strains. These findings establish conditions that result in vegetative cell and spore elimination and illustrate the resistance of C. difficile to common decontamination methods. These results further demonstrate that the vegetative cells and spores of various C. difficile strains have different resistance properties that may impact decontamination of surfaces and hands.

TLR9 mediates S. aureus killing inside osteoblasts via induction of oxidative stress

Background

Staphylococcus aureus is the principle causative pathogen of osteomyelitis and implant-associated bone infections. It is able to invade and to proliferate inside osteoblasts thus avoiding antibiotic therapy and the host immune system. Therefore, development of alternative approaches to stimulate host innate immune responses could be beneficial in prophylaxis against S. aureus infection. TLR9 is the intracellular receptor which recognizes unmethylated bacterial CpG-DNA and activates immune cells. Synthetic CpG-motifs containing oligodeoxynucleotide (CpG-ODNs) mimics the stimulatory effect of bacterial DNA.

Results

Osteoblast-like SAOS-2 cells were pretreated with CpG-ODN type-A 2216, type-B 2006, or negative CpG-ODN 2243 (negative control) 4 h before infection with S. aureus isolate EDCC 5055 (=DSM 28763). Intracellular bacteria were streaked on BHI plates 4 h and 20 h after infection. ODN2216 as well as ODN2006 but not ODN2243 were able to significantly inhibit the intracellular bacterial growth because about 31 % as well as 43 % of intracellular S. aureus could survive the pretreatment of SAOS-2 cells with ODN2216 or ODN2006 respectively 4 h and 20 h post-infection. RT-PCR analysis of cDNAs from SAOS-2 cells showed that pretreatment with ODN2216 or ODN2006 stimulated the expression of TLR9. Pretreatment of SAOS-2 cells with ODN2216 or ODN2006 but not ODN2243 managed to induce reactive oxygen species (ROS) production inside osteoblasts as measured by flow cytometry analysis. Moreover, treating SAOS-2 cells with the antioxidant Diphenyleneiodonium (DPI) obviously reduced S. aureus killing ability of TLR9 agonists mediated by oxidative stress.

Conclusions

In this work we demonstrated for the first time that CPG-ODNs have inhibitory effects on S. aureus survival inside SAOS-2 osteoblast-like cell line. This effect was attributed to stimulation of TLR9 and subsequent induction of oxidative stress. Pretreatment of infected SAOS-2 cells with ROS inhibitors resulted in the abolishment of the CPG-ODNs killing effects.