Distinctive cytokines as biomarkers predicting fatal outcome of severe Staphylococcus aureus bacteremia in mice

Novel biosynthesis of tellurium nanoparticles and investigation of their activity against common pathogenic bacteria

Objectives

Tellurium has received substantial attention for its remarkable properties. This study performed in vitro and in vivo testing of the antibacterial action of tellurium nanoparticles biosynthesized in actinomycetes against methicillin-resistant Staphylococcus aureus (MRSA), a common blood bacterial pathogen.

Methods

Nine actinomycete isolates were tested for their potential to reduce potassium tellurite (K₂TeO₃) and form tellurium nanoparticles (TeNPs). The most efficient actinomycete isolate in producing Tellerium nanoparticles was identified through molecular protocols. The generated TeNPs were characterized using UV, TEM, EDX, XRD and FTIR. The bacterial species implicated in bloodstream infections were detected at El Hussein Hospital. Bacterial identification and antibiotic susceptibility testing were performed using Vitek 2. An animal infection model was used to test the efficacy of the produced TeNPs against the most commonly isolated methicillin-resistant S. aureus using survival assays, colony counting, cytokine assessment and biochemical testing.

Results

The most efficient actinomycete isolate was identified as Streptomyces graminisoli and given the accession number (OL773539). The mean particle size of the produced TeNPs was 21.4 nm, and rods and rosette forms were observed. Methicillin-resistant S. aureus (MRSA) was the main bacterium (60%) causing blood stream infections, and was followed by Escherichia coli (25%) and Klebsiella pneumoniae (15%). The produced TeNPs were tested against MRSA, the bacterium most frequently isolated from blood, and showed a promising action inhibition zone of 24 ± 0.7 mm and an MIC of 50 μg/ml. An animal infection model indicated the promise of TeNPs alone or in combination with standard drugs to combat MRSA in a rat intravenous infection model.

Conclusion

TeNPs combined with vancomycin have successive impact to combat bacteremia for further verification of results.

Bactericidal fully human single-chain fragment variable antibodies protect mice against methicillin-resistant Staphylococcus aureus bacteraemia

OBJECTIVES

The increasing prevalence of antibiotic-resistant Staphylococcus aureus, besides the inadequate numbers of effective antibiotics, emphasises the need to find new therapeutic agents against this lethal pathogen.

METHODS

In this study, to obtain antibody fragments against S. aureus, a human single-chain fragment variable (scFv) library was enriched against living methicillin-resistant S. aureus (MRSA) cells, grown in three different conditions, that is human peripheral blood mononuclear cells with plasma, whole blood and biofilm. The antibacterial activity of scFvs was evaluated by the growth inhibition assay in vitro. Furthermore, the therapeutic efficacy of anti-S. aureus scFvs was appraised in a mouse model of bacteraemia.

RESULTS

Three scFv antibodies, that is MEH63, MEH158 and MEH183, with unique sequences, were found, which exhibited significant binding to S. aureus and reduced the viability of S. aureus in in vitro inhibition assays. Based on the results, MEH63, MEH158 and MEH183, in addition to their combination, could prolong the survival rate, reduce the bacterial burden in the blood and prevent inflammation and tissue destruction in the kidneys and spleen of mice with MRSA bacteraemia compared with the vehicle group (treated with normal saline).

CONCLUSION

The combination therapy with anti-S. aureus scFvs and conventional antibiotics might shed light on the treatment of patients with S. aureus infections.

HIF1α inhibition facilitates Leflunomide-AHR-CRP signaling to attenuate bone erosion in CRP-aberrant rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by progressive bone erosion. Leflunomide is originally developed to suppress inflammation via its metabolite A77 1726 to attenuate bone erosion. However, distinctive responsiveness to Leflunomide is observed among RA individuals. Here we show that Leflunomide exerts immunosuppression but limited efficacy in RA individuals distinguished by higher serum C-reactive protein (CRP^Higher, CRP^H), whereas the others with satisfactory responsiveness to Leflunomide show lower CRP (CRP^Lower, CRP^L). CRP inhibition decreases bone erosion in arthritic rats. Besides the immunomodulation via A77 1726, Leflunomide itself induces AHR-ARNT interaction to inhibit hepatic CRP production and attenuate bone erosion in CRP^L arthritic rats. Nevertheless, high CRP in CRP^H rats upregulates HIF1α, which competes with AHR for ARNT association and interferes Leflunomide-AHR-CRP signaling. Hepatocyte-specific HIF1α deletion or a HIF1α inhibitor Acriflavine re-activates Leflunomide-AHR-CRP signaling to inhibit bone erosion. This study presents a precision medicine-based therapeutic strategy for RA.

Leflunomide is used for the treatment of rheumatoid arthritis. Here, the authors show that effectiveness is limited in patients with higher levels of serum c-reactive protein (CRP). Using animal models, they show that higher CRP induces HIF1a expression, which in turn interferes with Leflunomide signalling, and that effectiveness of the drug is restored when HIF1a is pharmacologically inhibited.

Staphylococcus aureus SaeR/S-Regulated Factors Decrease Monocyte-Derived Tumor Necrosis Factor-α to Reduce Neutrophil Bactericidal Activity

Background

The ability of Staphylococcus aureus to evade killing by human neutrophils significantly contributes to disease progression. In this study, we characterize an influential role for the S. aureus SaeR/S 2-component gene regulatory system in suppressing monocyte production of tumor necrosis factor alpha (TNF-α) to subsequently influence human neutrophil priming.

Methods

Using flow cytometry and TNF-α specific enzyme-linked immunosorbent assays we identify the primary cellular source of TNF-α in human blood and in purified peripheral blood mononuclear cells (PBMCs) during interaction with USA300 and an isogenic saeR/S deletion mutant (USA300∆saeR/S). Assays with conditioned media from USA300 and USA300∆saeR/S exposed PBMCs were used to investigate priming on neutrophil bactericidal activity.

Results

TNF-α production from monocytes was significantly reduced following challenge with USA300 compared to USA300∆saeR/S. We observed that priming of neutrophils using conditioned medium from peripheral blood mononuclear cells stimulated with USA300∆saeR/S significantly increased neutrophil bactericidal activity against USA300 relative to unprimed neutrophils and neutrophils primed with USA300 conditioned medium. The increased neutrophil bactericidal activity was associated with enhanced reactive oxygen species production that was significantly influenced by elevated TNF-α concentrations.

Conclusions

Our findings identify an immune evasion strategy used by S. aureus to impede neutrophil priming and subsequent bactericidal activity.

Host Nitric Oxide Disrupts Microbial Cell-to-Cell Communication to Inhibit Staphylococcal Virulence

Staphylococcus aureus is a commensal bacterium that can asymptomatically colonize its host but also causes invasive infections. Quorum sensing regulates S. aureus virulence and the transition from a commensal to a pathogenic organism. However, little is known about how host innate immunity affects interbacterial communication. We show that nitric oxide suppresses staphylococcal virulence by targeting the Agr quorum sensing system. Nitric oxide-mediated inhibition occurs through direct modification of cysteine residues C55, C123, and C199 of the AgrA transcription factor. Cysteine modification decreases AgrA promoter occupancy as well as transcription of the agr operon and quorum sensing-activated toxin genes. In a staphylococcal pneumonia model, mice lacking inducible nitric oxide synthase develop more severe disease with heightened mortality and proinflammatory cytokine responses. In addition, staphylococcal α-toxin production increases in the absence of nitric oxide or nitric oxide-sensitive AgrA cysteine residues. Our findings demonstrate an anti-virulence mechanism for nitric oxide in innate immunity.

Experimental Sepsis Severity Score Associated to Mortality and Bacterial Spreading is Related to Bacterial Load and Inflammatory Profile of Different Tissues

Pneumonia-induced sepsis is responsible for about 50% of cases in the world. Patients who develop severe sepsis and septic shock present organ dysfunction and elevated plasma cytokine levels, which may lead to death. Clinical scores are important to evaluate the framework of septic patients and are used to predict the syndrome progress, prognostics, and mortality. The objective of the present study was to verify the applicability of a murine clinical score system to experimental sepsis (pneumonia-induced sepsis in male mice) and to correlate it with mortality and bacterial dissemination in different organs. Results demonstrated that animals which present higher clinical scores (>3) are more likely to die. Animals presenting high clinical scores exhibited transient bacteremia and displayed bacterial spreading to different organs such as heart, kidney, liver, and brain. There is a correlation between clinical score and bacterial dissemination and consequently greater risk of death. In addition, animals which showed bacterial dissemination in more than three organs and high clinical scores presented high levels of cytokines (TNF-α, MCP-1, IL-6, and IL-10) in plasma, lung, heart, liver, kidney, and brain. Therefore, our study suggests that (1) severity scores have predictive power in experimental models of sepsis and (2) high concentrations of tissue cytokines may contribute to localized inflammation and be one of the factors responsible for the systemic inflammatory syndrome of sepsis.

Staphylococcus aureus Induces Shedding of IL-1RII in Monocytes and Neutrophils

Interleukin 1 (IL-1) β is a critical cytokine that orchestrates host defenses against Staphylococcus aureus and is crucial for the eradication of bacteria. The production and action of IL-1β are regulated by multiple control pathways. Among them, IL-1RII (the type II IL-1 receptor) acts as a decoy receptor and has been shown to regulate the biological effects of IL-1β. High levels of soluble IL-1RII are present in septic patients; however, the stimuli that regulate the expression and release of IL-1RII in pathological conditions are incompletely elucidated. In the present study, we demonstrated the ability of S. aureus and protein A to induce IL-1RII shedding in myeloid cells. The positive modulation of IL-1RII expression and cleavage was associated with the failure to detect IL-1β in response to S. aureus both in vitro and in vivo, suggesting that the soluble form of the receptor could be masking the availability of IL-1β. The absence of detectable IL-1β was associated with low levels of inflammatory cytokines and chemokines known to be regulated by IL-1β and with increased bacterial persistence. Modulation of decoy receptors during systemic S. aureus infection is proposed as a new strategy used by this bacterium to evade the immune response.

Implant Placement in Failed Endodontic Sites: A Review

Dental implants may fail to osseointegrate in sites of endodontic failure. This may occur as a result colonization by various anaerobic and facultative bacterial species. If an implant is placed in a site where vegetative bacteria are residing, the implant may fail to integrate if a bacterial colonization proceeds coronally. If the implant apical cortical bone is thin or if there is an apical fenestration, the colonization may proceed through the thin or nonexistent bone through the covering mucosa, relieving inflammatory pressure to create an apical (retrograde) peri-implantitis. Enterococcus faecalis may be the prime culprit in these types of implant failures. After thorough debridement, the implant may be immediately placed after extraction of an endodontically failed tooth, and the patient treated with an appropriate antibiotic. Alternatively waiting for postextraction healing and subsequent implant placement can be done. Nevertheless, either way may allow for the formation of bacterial vegetative forms or biofilms. The implant surface may be colonized when the surface is exposed to the bacteria. Thorough debridement is crucial. Nonetheless, organisms may persist. Randomized controlled trials are needed to elucidate this issue.

Estradiol protects female rats against sepsis induced by Enterococcus faecalis improving leukocyte bactericidal activity

Enterococcus faecalis is a Gram-positive bacteria described as an important causative agent of sepsis. The contact between host leukocytes and bacteria activates the innate immunity, participating as the first defense mechanism against infection. Pro-inflammatory cytokines [including tumor necrosis factor (TNF)-α and interleukin-1β] and nitric oxide (NO) are essential to recruitment of leukocytes into the infectious focus as well as their activation for phagocytosis. Beyond the bacteria species, gender has been considered another factor to predict outcome in septic patients. Studies suggest that females exhibit a protective advantage during sepsis models, being gonadal hormones possible modulators of functions of immune cells. Nevertheless, the role of estradiol during Gram-positive infection remains a literature gap. Our aims were to investigate whether estradiol protects rats against bacterial dissemination during E. faecalis-induced sepsis. We determined whether estradiol modulates the local and systemic inflammatory response, as well as the cell migration into the infectious focus and the bactericidal capacity of leukocytes. Our findings demonstrated that estradiol pre-treated rats showed a dose-dependent reduction in bacterial counts in peritoneal lavage fluid (PLF) and in liver. Moreover, TNF-α and nitrate levels were increased in plasma, while only TNF-α was increased in the PLF in estradiol-treated rats. The prevention of bacterial dissemination may be related to the enhanced neutrophil and macrophage migration into the peritoneal cavity. Furthermore, estradiol improved the phagocytic and bactericidal ability of these both inflammatory cells. Taken together, the present study clearly demonstrates an important protective role of estradiol against sepsis induced by E. faecalis in female rats.

Mild Staphylococcus aureus Skin Infection Improves the Course of Subsequent Endogenous S. aureus Bacteremia in Mice

Staphylococcus aureus carriers with S. aureus bacteremia may have a reduced mortality risk compared to non-carriers. A role for the immune system is suggested. Here, we study in mice the effect of mild S. aureus skin infection prior to endogenous or exogenous S. aureus bacteremia, and evaluate protection in relation to anti-staphylococcal antibody levels. Skin infections once or twice by a clinical S. aureus isolate (isolate P) or S. aureus strain 8325-4 were induced in mice free of S. aureus and anti-staphylococcal antibodies. Five weeks later, immunoglobulin G (IgG) levels in blood against 25 S. aureus antigens were determined, and LD50 or LD100 bacteremia caused by S. aureus isolate P was induced. S. aureus skin infections led to elevated levels of anti-staphylococcal IgG in blood. One skin infection improved the course of subsequent severe endogenous bacteremia only. A second skin infection further improved animal survival rate, which was associated with increased pre-bacteremia IgG levels against Efb, IsaA, LukD, LukE, Nuc, PrsA and WTA. In conclusion, S. aureus isolate P skin infection in mice reduces the severity of subsequent endogenous S. aureus bacteremia only. Although cellular immune effects cannot be rules out, anti-staphylococcal IgG against specified antigens may contribute to this effect.

Active immunization with an octa-valent Staphylococcus aureus antigen mixture in models of S. aureus bacteremia and skin infection in mice

Proteomic studies with different Staphylococcus aureus isolates have shown that the cell surface-exposed and secreted proteins IsaA, LytM, Nuc, the propeptide of Atl (pro-Atl) and four phenol-soluble modulins α (PSMα) are invariantly produced by this pathogen. Therefore the present study was aimed at investigating whether these proteins can be used for active immunization against S. aureus infection in mouse models of bacteremia and skin infection. To this end, recombinant His-tagged fusions of IsaA, LytM, Nuc and pro-Atl were isolated from Lactococcus lactis or Escherichia coli, while the PSMα1-4 peptides were chemically synthesized. Importantly, patients colonized by S. aureus showed significant immunoglobulin G (IgG) responses against all eight antigens. BALB/cBYJ mice were immunized subcutaneously with a mixture of the antigens at day one (5 μg each), and boosted twice (25 μg of each antigen) with 28 days interval. This resulted in high IgG responses against all antigens although the response against pro-Atl was around one log lower compared to the other antigens. Compared to placebo-immunized mice, immunization with the octa-valent antigen mixture did not reduce the S. aureus isolate P load in blood, lungs, spleen, liver, and kidneys in a bacteremia model in which the animals were challenged for 14 days with a primary load of 3 × 10⁵ CFU. Discomfort scores and animal survival rates over 14 days did not differ between immunized mice and placebo-immunized mice upon bacteremia with S. aureus USA300 (6 × 10⁵ CFU). In addition, this immunization did not reduce the S. aureus isolate P load in mice with skin infection. These results show that the target antigens are immunogenic in both humans and mice, but in the used animal models do not result in protection against S. aureus infection.

A novel conditional platelet depletion mouse model reveals the importance of platelets in protection against Staphylococcus aureus bacteremia

BACKGROUND

Platelets are critical cells for maintaining vascular hemostasis, but their activities in other processes are becoming apparent. Specifically, the ability of platelets to recognize and respond to infectious agents is an important area of investigation. To understand the physiologic roles of platelets in vivo, most researchers have used antibody-mediated platelet depletion, which has certain limitations.

OBJECTIVE

To develop an optimal system with which to study the contribution of platelets to protection against S. aureus blood infection.

METHODS

Here, we describe a novel experimental model of conditional platelet depletion based on the Cre-recombinase cell ablation system. With this technology, the simian diphtheria toxin receptor was expressed in platelet factor 4-positive cells (megakaryocytes and platelets).

RESULTS

Systemic administration of diphtheria toxin every 48 h resulted in reduced platelet numbers that became undetectable after 6 days. Although platelets were depleted, no other blood cells were affected. With this newly developed model, the functional contributions of platelets to protection against Staphylococcus aureus bacteremia was examined. Platelet-depleted mice succumbed to infection more rapidly than wild-type mice, and had a significantly higher bacterial burden in kidneys, elevated levels of serum markers of kidney damage, and increased levels of cytokines indicative of septic shock.

CONCLUSIONS

Here, we illustrate a new mouse model for conditional platelet depletion, and implicate platelets as important participants in the immune response to bacterial blood infections.

Pyroptosis of resident macrophages differentially orchestrates inflammatory responses to Staphylococcus aureus in resistant and susceptible mice

The relationship between Staphylococcus aureus and innate immunity is highly complex and requires further investigation to be deciphered. i.p. challenge of C57BL/6 and DBA/2 mice, resistant and susceptible to the infection, respectively, resulted in different patterns of cytokine production and neutrophil recruitment. Staphylococcus aureus infection induced macrophage pyroptosis, an inflammasome-dependent cell death program, whose rates significantly differed between C57BL/6 and DBA/2 mice. Fast rate pyroptosis of C57BL/6 macrophages released high levels of IL-1β but limited the synthesis of other cytokines such as TNF-α, IL-6, CXCL1, and CXCL2. Conversely, the extended survival of DBA/2 macrophages allowed substantial production of these NF-κB-related cytokines. Phenotyping of resting macrophages in different mouse strains revealed differential predisposition toward specific macrophage phenotypes that modulate S. aureus-mediated inflammasome activation. Treatment of DBA/2 susceptible mice with inflammasome inducers (i.e. nigericin and ATP) artificially increased pyroptosis and lowered the levels of NF-κB-related inflammatory cytokines, but restored IL-1β to levels similar to those in C57BL/6 mice. Collectively, this study promotes the concept that, in association with host genetics, the basal phenotype of resident macrophages influences the early inflammatory response and possibly participates in S. aureus infection outcome via the inflammasome pathway and subsequent pyroptosis.

A human monoclonal antibody targeting the conserved staphylococcal antigen IsaA protects mice against Staphylococcus aureus bacteremia

Due to substantial therapy failure and the emergence of antibiotic-resistant Staphylococcus aureus strains, alternatives for antibiotic treatment of S. aureus infections are urgently needed. Passive immunization using S. aureus-specific monoclonal antibodies (mAb) could be such an alternative to prevent and treat severe S. aureus infections. The invariantly expressed immunodominant staphylococcal antigen A (IsaA) is a promising target for passive immunization. Here we report the development of the human anti-IsaA IgG1 mAb 1D9, which was shown to bind to all 26 S. aureus isolates tested. These included both methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA, respectively). Immune complexes consisting of IsaA and 1D9 stimulated human as well as murine neutrophils to generate an oxidative burst. In a murine bacteremia model, the prophylactic treatment with a single dose of 5 mg/kg 1D9 improved the survival of mice challenged with S. aureus isolate P (MSSA) significantly, while therapeutic treatment with the same dose did not influence animal survival. Neither prophylactic nor therapeutic treatment with 5 mg/kg 1D9 resulted in improved survival of mice with S. aureus USA300 (MRSA) bacteremia. Importantly, our studies show that healthy S. aureus carriers elicit an immune response which is sufficient to generate protective mAbs against invariant staphylococcal surface antigens. Human mAb 1D9, possibly conjugated to for example another antibody, antibiotics, cytokines or chemokines, may be valuable to fight S. aureus infections in patients.

Prophylactic effect of human lactoferrin against Streptococcus mutans bacteremia in lactoferrin knockout mice

Streptococcus mutans is the primary agent of dental caries, which is often detected in transient bacteremia. Lactoferrin is a multifunctional glycoprotein showing antibacterial activities against several Streptococcus species. We reported here the prophylactic effect of human lactoferrin (hLF) in a lactoferrin knockout mouse (LFKO-/-) bacteremic model. The hLF treatment significantly cleared S. mutans from the blood and organs of bacteremic mice when compared to the non-hLF treated mice. Further, analysis of serum cytokines, spleen and liver cytokine mRNA levels revealed that hLF prophylaxis modulates their release differently when compared to the non-hLF treated group. C-reactive protein level (P = 0.003) also decreased following hLF prophylaxis in S. mutans induced bacteremic mice. Additional quantitative RT-PCR analysis revealed that hLF prophylaxis significantly decreased the expression level of IFN-γ, TNF-α, IL-1β, IL-6, MPO and iNOS in spleen and liver. These results suggested that the hLF protects the host against S. mutans-induced experimental bacteremia.

Protective effects of human lactoferrin during Aggregatibacter actinomycetemcomitans-induced bacteremia in lactoferrin-deficient mice

Aggregatibacter actinomycetemcomitans, a periodontopathogen, has been associated with several systemic diseases. Herein, we report the protective effect of human lactoferrin (hLF) during A. actinomycetemcomitans bacteremia in lactoferrin knockout (LFKO(-/-)) mice. The prophylactic, concurrent, and therapeutic intravenous (i.v.) administrations of hLF significantly cleared the bacteria from blood and organs. Nevertheless, all modes of hLF administration significantly decreased the concentrations of serum proinflammatory cytokines, such as interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), IL-6, IL-10, and IL-12p70. Additionally, hLF administration significantly decreased hepatic and splenic proinflammatory cytokine expression levels compared to those in the non-hLF-treated group. Furthermore, administration of hLF decreased the serum C-reactive protein level, inducible nitric oxide synthase (iNOS) and myeloperoxidase (MPO) gene expression levels in liver and spleen. hLF treatment has also resulted in a 6-fold decrease in spleen weight with the migration of typical inflammatory cells in infected mice as a result of decreased inflammatory response. These results reveal that hLF protects against A. actinomycetemcomitans bacteremia, as indicated by rapid bacterial clearance and decreased host proinflammatory mediators.

Development of an ELISA for the quantification of the C-terminal decapeptide prothymosin α(100-109) in sera of mice infected with bacteria

Apoptosis is characterized by a series of discrete biochemical events, among which is the truncation of the nuclear polypeptide prothymosin alpha (proTα) by activated caspase-3. This early apoptotic event results in the generation of a carboxy-terminal fragment of proTα, the immunoactive decapeptide proTα(100-109). We hypothesized that the detection of increased levels of proTα(100-109) in serum can be directly correlated with the induction of massive cell apoptosis, resulting from a severe bacterial infection. Thus, using high-affinity-purified polyclonal antibodies (Abs), raised in rabbits and a prototype antibody-capture system, we developed a highly sensitive and specific competitive ELISA for proTα(100-109). The sensitivity of the ELISA (0.1ng/mL to 10μg/mL) is acceptable for the quantification of the decapeptide in serum samples. To assess our initial hypothesis, we determined the concentration of proTα(100-109) in the sera of mice infected with the bacterium Streptococcus pyogenes over the course of the infection. We show that serum concentration of proTα(100-109) was marginal to undetectable before infection, increased over time and peaked at 72h postinfection. In silico analysis suggests that the Abs generated are unlikely to cross-react with any other unrelated mouse or bacterial protein. Further validation of our ELISA using serum samples from humans, infected with bacteria, may provide a useful tool to differentiate the causative agent of a potentially lethal septic infection.