Immunotherapy markedly increases the effectiveness of antimicrobial therapy for treatment of Burkholderia pseudomallei infection

Ceftazidime is a potential drug to inhibit cell proliferation by increasing cellular p27

The development of new therapeutic uses for existing drugs is important for the treatment of some diseases. Cephalosporin antibiotics stand as the most extensively utilized antibiotics in clinical practice, effectively combating bacterial infections. Here, we found that the antimicrobial drug ceftazidime strongly upregulates p27 protein levels by inhibiting p27 ubiquitination. The p27 protein is a classic negative regulator of the cell cycle. Next, we demonstrated that ceftazidime can impede the cell cycle from G1 to S phase, thus inhibiting cell proliferation. Furthermore, we found that ceftazidime promotes p27 expression and inhibits cell proliferation by reducing Skp2, which is a substrate recognition component of the Skp2-Cullin-F-box (SCF) ubiquitin ligase. Moreover, ceftazidime downregulates transcriptional expression of Skp2. Importantly, we demonstrated that ceftazidime inhibited the proliferation of tumor cells in vivo. These findings reveal ceftazidime-mediated inhibition of cell proliferation through the Skp2-p27 axis, and could provide a potential strategy for anti-tumor therapy.

Extracorporeal Membrane Oxygenation-Dependent Fulminant Melioidosis From Caspase 4 Mutation Reversed by Interferon Gamma Therapy

We describe bedside-to-bench immunological and genetic elucidation of defective pyroptosis attributable to novel caspase 4 defect mediating pathogen-triggered inflammatory programmed cell death, in the setting of severe pneumonia and abscess-forming melioidosis in an overtly healthy host failing to clear Burkholderia pseudomallei infection, and how targeted adjunctive biological therapy led to a successful outcome.

Evaluation of Immune Nanoparticles for Rapid and Non-Specific Activation of Antiviral and Antibacterial Immune Responses in Cattle, Swine, and Poultry

Given the rapid potential spread of agricultural pathogens, and the lack of vaccines for many, there is an important unmet need for strategies to induce rapid and non-specific immunity against these viral and bacterial threats. One approach to the problem is to generate non-specific immune responses at mucosal surfaces to rapidly protect from entry and replication of both viral and bacterial pathogens. Using complexes of charged nanoparticle liposomes with both antiviral and antibacterial toll-like receptor (TLR) nucleic acid ligands (termed liposome-TLR complexes or LTC), we have previously demonstrated considerable induction of innate immune responses in nasal and oropharyngeal tissues and protection from viral and bacterial pathogens in mixed challenge studies in rodents, cattle, and companion animals. Therefore, in the present study, we used in vitro assays to evaluate the ability of the LTC immune stimulant to activate key innate immune pathways, particularly interferon pathways, in cattle, swine, and poultry. We found that LTC complexes induced strong production of type I interferons (IFNα and IFNβ) in both macrophages and leukocyte cultures from all three species. In addition, the LTC complexes induced the production of additional key protective cytokines (IL-6, IFNγ, and TNFα) in macrophages and leukocytes in cattle and poultry. These findings indicate that the LTC mucosal immunotherapeutic has the capability to activate key innate immune defenses in three major agricultural species and potentially induce broad protective immunity against both viral and bacterial pathogens. Additional animal challenge studies are warranted to evaluate the protective potential of LTC immunotherapy in cattle, swine, and poultry.

Efficacy of ceftazidime in a murine model following a lethal aerosol exposure to Burkholderia pseudomallei

Melioidosis is an endemic disease in numerous tropical regions. Additionally, the bacterium that causes melioidosis, Burkholderia pseudomallei, has potential to be used as a biological weapon. Therefore, development of effective and affordable medical countermeasures to serve regions affected by the disease and to have medical countermeasures available in the event of a bioterrorism attack remains critical. The current study evaluated the efficacy of eight distinct acute phase ceftazidime treatment regimens administered therapeutically in the murine model. At the conclusion of the treatment period, survival rates were significantly greater in several of the treated groups when compared to the control group. Pharmacokinetics of a single dose of ceftazidime were examined at 150 mg/kg, 300 mg/kg, and 600 mg/kg and were compared to an intravenous clinical dose administered at 2000 mg every eight hours. The clinical dose has an estimated 100% fT > 4*MIC which exceeded the highest murine dose of 300 mg/kg every six hours at 87.2% fT > 4*MIC. Based upon survival at the end of the treatment regimen and supplemented by pharmacokinetic modeling, a daily dose of 1200 mg/kg of ceftazidime, administered every 6 h at 300 mg/kg, provides protection in the acute phase of inhalation melioidosis in the murine model.

Antimicrobial immunotherapeutics: past, present and future

In this age of antimicrobial resistance (AMR) there is an urgent need for novel antimicrobials. One area of recent interest is in developing antimicrobial effector molecules, and even cell-based therapies, based on those of the immune system. In this review, some of the more interesting approaches will be discussed, including immune checkpoint inhibitors, Interferons (IFNs), Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF), Chimeric Antigen Receptor (CAR) T cells, Antibodies, Vaccines and the potential role of trained immunity in protection from and/or treatment of infection.

Dietary antioxidant seleno-L-methionine protects macrophages infected with Burkholderia thailandensis

Burkholderia pseudomallei is a facultative intracellular pathogen and the causative agent of melioidosis, a potentially life-threatening disease endemic in Southeast Asia and Northern Australia. Treatment of melioidosis is a long and costly process and the pathogen is inherently resistant to several classes of antibiotics, therefore there is a need for new treatments that can help combat the pathogen. Previous work has shown that the combination of interferon-gamma, an immune system activator, and the antibiotic ceftazidime synergistically reduced the bacterial burden of RAW 264.7 macrophages that had been infected with either B. pseudomallei or Burkholderia thailandensis. The mechanism of the interaction was found to be partially dependent on interferon-gamma-induced production of reactive oxygen species inside the macrophages. To further confirm the role of reactive oxygen species in the effectiveness of the combination treatment, we investigated the impact of the antioxidant and reactive oxygen species scavenger, seleno-L-methionine, on intracellular and extracellular bacterial burden of the infected macrophages. In a dose-dependent manner, high concentrations of seleno-L-methionine (1000 μM) were protective towards infected macrophages, resulting in a reduction of bacteria, on its own, that exceeded the reduction caused by the antibiotic alone and rivaled the effect of ceftazidime and interferon-gamma combined. Seleno-L-methionine treatment also resulted in improved viability of infected macrophages compared to untreated controls. We show that the protective effect of seleno-L-methionine was partly due to its inhibition of bacterial growth. In summary, our study shows a role for high dose seleno-L-methionine to protect and treat macrophages infected with B. thailandensis.

Non-specific protection from respiratory tract infections in cattle generated by intranasal administration of an innate immune stimulant

Alternatives to antibiotics for prevention of respiratory tract infections in cattle are urgently needed given the increasing public and regulatory pressure to reduce overall antibiotic usage. Activation of local innate immune defenses in the upper respiratory tract is one strategy to induce non-specific protection against infection with the diverse array of viral and bacterial pathogens associated with bovine respiratory disease complex (BRDC), while avoiding the use of antibiotics. Our prior studies in rodent models demonstrated that intranasal administration of liposome-TLR complexes (LTC) as a non-specific immune stimulant generated high levels of protection against lethal bacterial and viral pathogens. Therefore, we conducted studies to assess LTC induction of local immune responses and protective immunity to BRDC in cattle. In vitro, LTC were shown to activate peripheral blood mononuclear cells in cattle, which was associated with secretion of INFγ and IL-6. Macrophage activation with LTC triggered intracellular killing of Mannheimia hemolytica and several other bacterial pathogens. In studies in cattle, intranasal administration of LTC demonstrated dose-dependent activation of local innate immune responses in the nasopharynx, including recruitment of monocytes and prolonged upregulation (at least 2 weeks) of innate immune cytokine gene expression by nasopharyngeal mucosal cells. In a BRDC challenge study, intranasal administration of LTC prior to pathogen exposure resulted in significant reduction in both clinical signs of infection and disease-associated euthanasia rates. These findings indicate that intranasal administration of a non-specific innate immune stimulant can be an effective method of rapidly generating generalized protection from mixed viral and bacterial respiratory tract infections in cattle.

Combating biothreat pathogens: ongoing efforts for countermeasure development and unique challenges

Research to discover and develop antibacterial and antiviral drugs with potent activity against pathogens of biothreat concern presents unique methodological and process-driven challenges. Herein, we review laboratory approaches for finding new antibodies, antibiotics, and antiviral molecules for pathogens of biothreat concern. Using high-throughput screening techniques, molecules that directly inhibit a pathogen’s entry, replication, or growth can be identified. Alternatively, molecules that target host proteins can be interesting targets for development when countering biothreat pathogens, due to the modulation of the host immune response or targeting proteins that interfere with the pathways required by the pathogen for replication. Monoclonal and cocktail antibody therapies approved by the Food and Drug Administration for countering anthrax and under development for treatment of Ebola virus infection are discussed. A comprehensive tabular review of current in vitro, in vivo, pharmacokinetic and efficacy datasets has been presented for biothreat pathogens of greatest concern. Finally, clinical trials and animal rule or traditional drug approval pathways are also reviewed.

Opinions; interpretations; conclusions; and recommendations are those of the authors and are not necessarily endorsed by the US Army.

Emerging role of biologics for the treatment of melioidosis and glanders

Introduction: Two important pathogenic species within the genus Burkholderia, namely Burkholderia pseudomallei (Bpm) and Burkholderia mallei (Bm), are the causative agents of the life-threatening diseases melioidosis and glanders, respectively. Due to their high mortality rate and potential for aerosolization, they have gained interest as potential biothreat agents and are classified as Tier 1 Select Agents.Areas covered: The manuscript provides an overview of the literature covering the efforts taken in the last 10 years to develop new therapeutics measures against both Bpm and Bm, with attention on novel therapeutic agents.Expert Opinion: As a result of the complicated antibiotic regimens necessary to treat these infections, development of novel therapeutics is needed to treat both diseases. In recent years, the understanding of the pathogenesis of Burkholderia has improved significantly and so have the efforts to develop novel therapeutic agents with high efficacy, either alone, or in combination with conventional antibiotics.

GC-072: A Novel Therapeutic Candidate for Oral Treatment of Melioidosis and Infections Caused by Select Biothreat Pathogens

Burkholderia pseudomallei (B. pseudomallei), the etiological agent of melioidosis, is a Gram-negative bacterium with additional concern as a biothreat pathogen. The mortality rate from B. pseudomallei varies depending on the type of infection and extent of available health care, but in the case of septicemia left untreated it can range from 50 - 90%. Current therapy for melioidosis is biphasic, consisting of parenteral acute-phase treatment for two weeks or longer, followed by oral eradication-phase treatment lasting several months. An effective oral therapeutic for outpatient treatment of acute-phase melioidosis is needed. GC-072 is a potent, 4-oxoquinolizine antibiotic with selective inhibitory activity against bacterial topoisomerases. GC-072 has demonstrated in vitro potency against susceptible and drug-resistant strains of B. pseudomallei and is also active against Burkholderia mallei, Bacillus anthracis, Yersinia pestis, and Francisella tularensis GC-072 is bactericidal both extra- and intracellularly, with rapid killing noted within a few hours and reduced development of resistance compared to ceftazidime. GC-072, delivered intragastrically to mimic oral administration, promoted dose-dependent survival in mice using lethal inhalational models of B. pseudomallei infection following exposure to a 24 or 339 LD50 challenge with B. pseudomallei strain 1026b. Overall, GC-072 appears to be a strong candidate for first-line, oral treatment of melioidosis.

The treatment of melioidosis: is there a role for repurposed drugs? A proposal and review

Introduction: Melioidosis is a significant health problem within endemic areas such as Southeast Asia and Northern Australia. The varied presentation of melioidosis and the intrinsic antibiotic resistance of Burkholderia pseudomallei, the causative organism, make melioidosis a difficult infection to manage. Often prolonged courses of antibiotic treatments are required with no guarantee of clinical success.Areas covered: B. pseudomallei is able to enter phagocytic cells, affect immune function, and replicate, via manipulation of the caspase system. An examination of this mechanism, and a look at other factors in the pathogenesis of melioidosis, shows that there are multiple potential points of therapeutic intervention, some of which may be complementary. These include the directed use of antimicrobial compounds, blocking virulence mechanisms, balancing or modulating cytokine responses, and ameliorating sepsis.Expert commentary: There may be therapeutic options derived from drugs in clinical use for unrelated conditions that may have benefit in melioidosis. Key compounds of interest primarily affect the disequilibrium of the cytokine response, and further preclinical work is needed to explore the utility of this approach and encourage the clinical research needed to bring these into beneficial use.

Central nervous system melioidosis in the pediatric age group: review

PURPOSE

Melioidosis is a potentially fatal infectious disease caused by Burkholderia pseudomallei. Neurologic involvement in pediatric age group is very rare, and only a handful of cases have been reported in literature. We sought to provide a systematic review of pediatric neurologic melioidosis.

METHODS

Literature review was performed to analyze reported cases of pediatric neurologic melioidosis (≤16 years) by searching online database (PubMed/MEDLINE).

RESULTS

Twenty-seven cases were analyzed. Mean age was 6.7 years (range 2 days-14 years) and around 50% were older children (>5 years). Cranial nerve palsies and fever were most common presenting features. Major manifestations were meningoencephalitis in 16 (59%) and cerebral abscesses in eight (29%) cases. Abscesses were mostly located in parietal lobe. Among older children, abscesses were common than meningeal disease, while being converse for neonates. Mean follow-up duration was 11.5 months. Ten cases showed good to excellent outcome, while eight cases had fair (incomplete recovery) outcomes. The overall mortality rate was 18.5% (5/27) and tends to decrease with age. Among the five deaths, 4 (80%) had septicemia or pneumonia.

CONCLUSIONS

Pediatric neurologic melioidosis is very rare. Meningoencephalitis is the most common presentation. Mortality is the highest in neonates. Ceftazidime appears to be the drug of choice in intensive phase, although the best drug in maintenance phase cannot be commented upon, especially in very young children.

Three-factor models versus time series models: quantifying time-dependencies of interactions between stimuli in cell biology and psychobiology for short longitudinal data

Signal integration determines cell fate on the cellular level, affects cognitive processes and affective responses on the behavioural level, and is likely to be involved in psychoneurobiological processes underlying mood disorders. Interactions between stimuli may subjected to time effects. Time-dependencies of interactions between stimuli typically lead to complex cell responses and complex responses on the behavioural level. We show that both three-factor models and time series models can be used to uncover such time-dependencies. However, we argue that for short longitudinal data the three factor modelling approach is more suitable. In order to illustrate both approaches, we re-analysed previously published short longitudinal data sets. We found that in human embryonic kidney 293 cells cells the interaction effect in the regulation of extracellular signal-regulated kinase (ERK) 1 signalling activation by insulin and epidermal growth factor is subjected to a time effect and dramatically decays at peak values of ERK activation. In contrast, we found that the interaction effect induced by hypoxia and tumour necrosis factor-alpha for the transcriptional activity of the human cyclo-oxygenase-2 promoter in HEK293 cells is time invariant at least in the first 12-h time window after stimulation. Furthermore, we applied the three-factor model to previously reported animal studies. In these studies, memory storage was found to be subjected to an interaction effect of the beta-adrenoceptor agonist clenbuterol and certain antagonists acting on the alpha-1-adrenoceptor / glucocorticoid-receptor system. Our model-based analysis suggests that only if the antagonist drug is administer in a critical time window, then the interaction effect is relevant.

Melioidosis: Clinical impact and public health threat in the tropics

This review briefly summarizes the geographical distribution and clinical impact of melioidosis, especially in the tropics. Burkholderia pseudomallei (a gram-negative bacterium) is the major causative agent for melioidosis, which is prevalent in Singapore, Malaysia, Thailand, Vietnam, and Northern Australia. Melioidosis patients are increasingly being recognized in other parts of the world. The bacteria are intrinsically resistant to many antimicrobial agents, but prolonged treatment, especially with combinations of antibiotics, may be effective. Despite therapy, the overall case fatality rate of septicemia in melioidosis remains significantly high. Intracellular survival of the bacteria within macrophages may progress to chronic infections, and about 10% of patients suffer relapses. In the coming decades, melioidosis will increasingly afflict travelers throughout many global regions. Clinicians managing travelers returning from the subtropics or tropics with severe pneumonia or septicemia should consider acute melioidosis as a differential diagnosis. Patients with open skin wounds, diabetes, or chronic renal disease are at higher risk for melioidosis and should avoid direct contact with soil and standing water in endemic regions. Furthermore, there are fears that B. pseudomallei may be used as a biological weapon. Technological advancements in molecular diagnostics and antibiotic therapy are improving the disease outcomes in endemic areas throughout Asia. Research and development efforts on vaccine candidates against melioidosis are ongoing.

Melioidosis and glanders modulation of the innate immune system: barriers to current and future vaccine approaches

Burkholderia pseudomallei and Burkholderia mallei are pathogenic bacteria causing fatal infections in animals and humans. Both organisms are classified as Tier 1 Select Agents owing to their highly fatal nature, potential/prior use as bioweapons, severity of disease via respiratory exposure, intrinsic resistance to antibiotics, and lack of a current vaccine. Disease manifestations range from acute septicemia to chronic infection, wherein the facultative intracellular lifestyle of these organisms promotes persistence within a broad range of hosts. This ability to thrive intracellularly is thought to be related to exploitation of host immune response signaling pathways. There are currently considerable gaps in our understanding of the molecular strategies employed by these pathogens to modulate these pathways and evade intracellular killing. A better understanding of the specific molecular basis for dysregulation of host immune responses by these organisms will provide a stronger platform to identify novel vaccine targets and develop effective countermeasures.

Nitrate, nitrite and nitric oxide reductases: from the last universal common ancestor to modern bacterial pathogens

The electrochemical gradient that ensues from the enzymatic activity of cytochromes such as nitrate reductase, nitric oxide reductase, and quinol oxidase contributes to the bioenergetics of the bacterial cell. Reduction of nitrogen oxides by bacterial pathogens can, however, be uncoupled from proton translocation and biosynthesis of ATP or NH4(+), but still linked to quinol and NADH oxidation. Ancestral nitric oxide reductases, as well as cytochrome c oxidases and quinol bo oxidases evolved from the former, are capable of binding and detoxifying nitric oxide to nitrous oxide. The NO-metabolizing activity associated with these cytochromes can be a sizable source of antinitrosative defense in bacteria during their associations with host cells. Nitrosylation of terminal cytochromes arrests respiration, reprograms bacterial metabolism, stimulates antioxidant defenses and alters antibiotic cytotoxicity. Collectively, the bioenergetics and regulation of redox homeostasis that accompanies the utilization of nitrogen oxides and detoxification of nitric oxide by cytochromes of the electron transport chain increases fitness of many Gram-positive and -negative pathogens during their associations with invertebrate and vertebrate hosts.

A reverse-phase protein microarray-based screen identifies host signaling dynamics upon Burkholderia spp. infection

Burkholderia is a diverse genus of gram-negative bacteria that causes high mortality rate in humans, equines and cattle. The lack of effective therapeutic treatments poses serious public health threats. Developing insights toward host-Burkholderia spp. interaction is critical for understanding the pathogenesis of infection as well as identifying therapeutic targets for drug development. Reverse-phase protein microarray technology was previously proven to identify and characterize novel biomarkers and molecular signatures associated with infectious disease and cancer. In the present study, this technology was utilized to interrogate changes in host protein expression and phosphorylation events in macrophages infected with a collection of geographically diverse strains of Burkholderia spp. The expression or phosphorylation state of 25 proteins was altered during Burkholderia spp. infections of which eight proteins were selected for further characterization by immunoblotting. Increased phosphorylation of AMPK-α1, Src, and GSK3β suggested the importance of their roles in regulating Burkholderia spp. mediated innate immune response. Modulating the inflammatory response by perturbing their activities may provide therapeutic routes for future treatments.

Mycobacterium tuberculosis evolutionary pathogenesis and its putative impact on drug development

Mycobacterium tuberculosis, the etiological agent of human TB, is the most important mycobacterial pathogen in terms of global patient numbers and gravity of disease. The molecular mechanisms by which M. tuberculosis causes disease are complex and the result of host-pathogen coevolution that might have started already in the time of its Mycobacterium canettii-like progenitors. Despite research progress, M. tuberculosis still holds many secrets of its successful strategy for circumventing host defences, persisting in the host and developing resistance, which makes anti-TB treatment regimens extremely long and often inefficient. Here, we discuss what we have learned from recent studies on the evolution of the pathogen and its putative new drug targets that are essential for mycobacterial growth under in vitro or in vivo conditions.

Efficacy of postexposure therapy against glanders in mice

Burkholderia mallei, the causative agent of glanders, is a CDC Tier 1 Select Agent for which there is no preventive vaccine and antibiotic therapy is difficult. In this study, we show that a combination of vaccination using killed cellular vaccine and therapy using moxifloxacin, azithromycin, or sulfamethoxazole-trimethoprim can protect BALB/c mice from lethal infection even when given 5 days after infectious challenge. Vaccination only, or antibiotic therapy only, was not efficacious. Although antibiotics evaluated experimentally can protect when given before or 1 day after challenge, this time course is not realistic in the cases of natural infection or biological attack, when the patient seeks treatment after symptoms develop or after a biological attack has been confirmed and the agent has been identified. Antibiotics can be efficacious after a prolonged interval between exposure and treatment, but only if the animals were previously vaccinated.

The impact of "omic" and imaging technologies on assessing the host immune response to biodefence agents

Understanding the interactions between host and pathogen is important for the development and assessment of medical countermeasures to infectious agents, including potential biodefence pathogens such as Bacillus anthracis, Ebola virus, and Francisella tularensis. This review focuses on technological advances which allow this interaction to be studied in much greater detail. Namely, the use of “omic” technologies (next generation sequencing, DNA, and protein microarrays) for dissecting the underlying host response to infection at the molecular level; optical imaging techniques (flow cytometry and fluorescence microscopy) for assessing cellular responses to infection; and biophotonic imaging for visualising the infectious disease process. All of these technologies hold great promise for important breakthroughs in the rational development of vaccines and therapeutics for biodefence agents.

Nitric oxide from IFNγ-primed macrophages modulates the antimicrobial activity of β-lactams against the intracellular pathogens Burkholderia pseudomallei and Nontyphoidal Salmonella

Our investigations show that nonlethal concentrations of nitric oxide (NO) abrogate the antibiotic activity of β-lactam antibiotics against Burkholderia pseudomallei, Escherichia coli and nontyphoidal Salmonella enterica serovar Typhimurium. NO protects B. pseudomallei already exposed to β-lactams, suggesting that this diatomic radical tolerizes bacteria against the antimicrobial activity of this important class of antibiotics. The concentrations of NO that elicit antibiotic tolerance repress consumption of oxygen (O₂), while stimulating hydrogen peroxide (H₂O₂) synthesis. Transposon insertions in genes encoding cytochrome c oxidase-related functions and molybdenum assimilation confer B. pseudomallei a selective advantage against the antimicrobial activity of the β-lactam antibiotic imipenem. Cumulatively, these data support a model by which NO induces antibiotic tolerance through the inhibition of the electron transport chain, rather than by potentiating antioxidant defenses as previously proposed. Accordingly, pharmacological inhibition of terminal oxidases and nitrate reductases tolerizes aerobic and anaerobic bacteria to β-lactams. The degree of NO-induced β-lactam antibiotic tolerance seems to be inversely proportional to the proton motive force (PMF), and thus the dissipation of ΔH⁺ and ΔΨ electrochemical gradients of the PMF prevents β-lactam-mediated killing. According to this model, NO generated by IFNγ-primed macrophages protects intracellular Salmonella against imipenem. On the other hand, sublethal concentrations of imipenem potentiate the killing of B. pseudomallei by NO generated enzymatically from IFNγ-primed macrophages. Our investigations indicate that NO modulates the antimicrobial activity of β-lactam antibiotics.

β-lactam drugs that inhibit peptidoglycan biosynthesis are often used in the treatment of bacterial infections, including melioidosis. Independent of their antibiotic activity, we have noted that submicromolar concentrations of β-lactams potentiate the killing of intracellular B. pseudomallei supported by NO generated by IFNγ-primed macrophages. The production of NO can nonetheless be a double-edged sword, as indicated by our observations that sublethal concentrations of nitric oxide (NO), a diatomic radical produced by phylogenetically diverse organisms to regulate neurotransmission, vascular tone and host defense, tolerize B. pseudomallei, nontyphoidal Salmonella and E. coli against the antimicrobial activity of β-lactams. Accordingly, NO produced in the inflammatory response of macrophages protects nontyphoidal Salmonella against β-lactam antibiotics. NO mediates bacterial tolerance to β-lactam antibiotics by inhibiting the electrochemical gradient supported by terminal cytochrome oxidases of the respiratory chain, rather than by decreasing oxidative stress as previously thought.

Interaction of Interferon gamma-induced reactive oxygen species with ceftazidime leads to synergistic killing of intracellular Burkholderia pseudomallei

Burkholderia pseudomallei, a facultative intracellular pathogen, causes severe infections and is inherently refractory to many antibiotics. Previous studies from our group have shown that interferon gamma (IFN-γ) interacts synergistically with the antibiotic ceftazidime to kill bacteria in infected macrophages. The present study aimed to identify the underlying mechanism of that interaction. We first showed that blocking reactive oxygen species (ROS) pathways reversed IFN-γ- and ceftazidime-mediated killing, which led to our hypothesis that IFN-γ-induced ROS interacted with ceftazidime to synergistically kill Burkholderia bacteria. Consistent with this hypothesis, we also observed that buthionine sulfoximine (BSO), another inducer of ROS, could substitute for IFN-γ to similarly potentiate the effect of ceftazidime on intracellular killing. Next, we observed that IFN-γ induced ROS-mediated killing of intracellular but not extracellular bacteria. On the other hand, ceftazidime effectively reduced extracellular bacteria but was not capable of intracellular killing when applied at 10 μg/ml. We investigated the exact role of IFN-γ-induced ROS responses on intracellular bacteria and notably observed a lack of actin polymerization associated with Burkholderia bacteria in IFN-γ-treated macrophages, which led to our finding that IFN-γ-induced ROS blocks vacuolar escape. Based on these results, we propose a model in which synergistically reduced bacterial burden is achieved primarily through separate and compartmentalized killing: intracellular killing by IFN-γ-induced ROS responses and extracellular killing by ceftazidime. Our findings suggest a means of enhancing antibiotic activity against Burkholderia bacteria through combination with drugs that induce ROS pathways or otherwise target intracellular spread and/or replication of bacteria.

Animal models for Francisella tularensis and Burkholderia species: scientific and regulatory gaps toward approval of antibiotics under the FDA Animal Rule

The development and regulatory approval of medical countermeasures (MCMs) for the treatment and prevention of bacterial threat agent infections will require the evaluation of products in animal models. To obtain regulatory approval, these models must accurately recapitulate aspects of human disease, including, but not necessarily limited to, route of exposure, time to disease onset, pathology, immune response, and mortality. This article focuses on the state of animal model development for 3 agents for which models are largely immature: Francisella tularensis, Burkholderia mallei, and Burkholderia pseudomallei. An overview of available models and a description of scientific and regulatory gaps are provided.

Host responses to melioidosis and tuberculosis are both dominated by interferon-mediated signaling

Melioidosis (Burkholderia pseudomallei infection) is a common cause of community-acquired sepsis in Northeast Thailand and northern Australia. B. pseudomallei is a soil saprophyte endemic to Southeast Asia and northern Australia. The clinical presentation of melioidosis may mimic tuberculosis (both cause chronic suppurative lesions unresponsive to conventional antibiotics and both commonly affect the lungs). The two diseases have overlapping risk profiles (e.g., diabetes, corticosteroid use), and both B. pseudomallei and Mycobacterium tuberculosis are intracellular pathogens. There are however important differences: the majority of melioidosis cases are acute, not chronic, and present with severe sepsis and a mortality rate that approaches 50% despite appropriate antimicrobial therapy. By contrast, tuberculosis is characteristically a chronic illness with mortality <2% with appropriate antimicrobial chemotherapy. We examined the gene expression profiles of total peripheral leukocytes in two cohorts of patients, one with acute melioidosis (30 patients and 30 controls) and another with tuberculosis (20 patients and 24 controls). Interferon-mediated responses dominate the host response to both infections, and both type 1 and type 2 interferon responses are important. An 86-gene signature previously thought to be specific for tuberculosis is also found in melioidosis. We conclude that the host responses to melioidosis and to tuberculosis are similar: both are dominated by interferon-signalling pathways and this similarity means gene expression signatures from whole blood do not distinguish between these two diseases.

Mechanisms of antibiotic resistance in Burkholderia pseudomallei: implications for treatment of melioidosis

Burkholderia pseudomallei is the etiologic agent of melioidosis. This multifaceted disease is difficult to treat, resulting in high morbidity and mortality. Treatment of B. pseudomallei infections is lengthy and necessitates an intensive phase (parenteral ceftazidime, amoxicillin-clavulanic acid or meropenem) and an eradication phase (oral trimethoprim-sulfamethoxazole). The main resistance mechanisms affecting these antibiotics include enzymatic inactivation, target deletion and efflux from the cell, and are mediated by chromosomally encoded genes. Overproduction and mutations in the class A PenA β-lactamase cause ceftazidime and amoxicillin-clavulanic acid resistance. Deletion of the penicillin binding protein 3 results in ceftazidime resistance. BpeEF-OprC efflux pump expression causes trimethoprim and trimethoprim-sulfamethoxazole resistance. Although resistance is still relatively rare, therapeutic efficacies may be compromised by resistance emergence due to increased use of antibiotics in endemic regions. Novel agents and therapeutic strategies are being tested and, in some instances, show promise as anti-B. pseudomallei infectives.

Neurologic melioidosis in a child: unique clinical features and challenges of serologic diagnosis

We present the case of a child who exemplifies the difficulties in diagnosing neurologic melioidosis.

Post-exposure immunization against Francisella tularensis membrane proteins augments protective efficacy of gentamicin in a mouse model of pneumonic tularemia

Successful treatment of pneumonic infection with Francisella tularensis, the causative agent of tularemia, requires rapid initiation of antibiotic therapy, yet even then treatment failures may occur. Consequently, new treatments are needed to enhance the effectiveness of antimicrobial therapy for acute pneumonic tularemia. In a prior study, immunization with F. tularensis membrane protein fraction (MPF) antigens 3 days prior to challenge was reported to induce significant protection from inhalational challenge. We therefore hypothesized that MPF immunization might also be effective in enhancing infection control if combined with antibiotic therapy and administered after infection as post-exposure immunotherapy. To address this question, a 24h post-exposure treatment model of acute pulmonary Schu S4 strain of F. tularensis infection in BALB/c mice was used. Following exposure, mice were immunized with MPF and treated with low-dose gentamicin, alone or in combination and the effects on survival, bacterial burden and dissemination were assessed. We found that immunization with MPF significantly increased the effectiveness of subtherapeutic gentamicin for post-exposure treatment of pneumonic tularemia, with 100% of combination-treated mice surviving long-term. Bacterial burdens in the liver and spleen were significantly reduced in combination MPF-gentamicin treated mice at 7 days after challenge. Passively transferred antibodies against MPF antigens also increased the effectiveness of gentamicin therapy. Thus, we concluded that post-exposure immunization with MPF antigens was an effective means of enhancing conventional antimicrobial therapy for pneumonic tularemia.

Polysaccharide specific monoclonal antibodies provide passive protection against intranasal challenge with Burkholderia pseudomallei

Burkholderia pseudomallei is a Gram-negative bacillus that is the causative agent of melioidosis. The bacterium is inherently resistant to many antibiotics and mortality rates remain high in endemic areas. The lipopolysaccharide (LPS) and capsular polysaccharide (CPS) are two surface-associated antigens that contribute to pathogenesis. We previously developed two monoclonal antibodies (mAbs) specific to the CPS and LPS; the CPS mAb was shown to identify antigen in serum and urine from melioidosis patients. The goal of this study was to determine if passive immunization with CPS and LPS mAbs alone and in combination would protect mice from a lethal challenge with B. pseudomallei. Intranasal (i.n.) challenge experiments were performed with B. pseudomallei strains 1026b and K96423. Both mAbs provided significant protection when administered alone. A combination of mAbs was protective when low doses were administered. In addition, combination therapy provided a significant reduction in spleen colony forming units (cfu) compared to results when either the CPS or LPS mAbs were administered alone.

Nasal Acai polysaccharides potentiate innate immunity to protect against pulmonary Francisella tularensis and Burkholderia pseudomallei Infections

Pulmonary Francisella tularensis and Burkholderia pseudomallei infections are highly lethal in untreated patients, and current antibiotic regimens are not always effective. Activating the innate immune system provides an alternative means of treating infection and can also complement antibiotic therapies. Several natural agonists were screened for their ability to enhance host resistance to infection, and polysaccharides derived from the Acai berry (Acai PS) were found to have potent abilities as an immunotherapeutic to treat F. tularensis and B. pseudomallei infections. In vitro, Acai PS impaired replication of Francisella in primary human macrophages co-cultured with autologous NK cells via augmentation of NK cell IFN-γ. Furthermore, Acai PS administered nasally before or after infection protected mice against type A F. tularensis aerosol challenge with survival rates up to 80%, and protection was still observed, albeit reduced, when mice were treated two days post-infection. Nasal Acai PS administration augmented intracellular expression of IFN-γ by NK cells in the lungs of F. tularensis-infected mice, and neutralization of IFN-γ ablated the protective effect of Acai PS. Likewise, nasal Acai PS treatment conferred protection against pulmonary infection with B. pseudomallei strain 1026b. Acai PS dramatically reduced the replication of B. pseudomallei in the lung and blocked bacterial dissemination to the spleen and liver. Nasal administration of Acai PS enhanced IFN-γ responses by NK and γδ T cells in the lungs, while neutralization of IFN-γ totally abrogated the protective effect of Acai PS against pulmonary B. pseudomallei infection. Collectively, these results demonstrate Acai PS is a potent innate immune agonist that can resolve F. tularensis and B. pseudomallei infections, suggesting this innate immune agonist has broad-spectrum activity against virulent intracellular pathogens.

Combining vaccination and postexposure CpG therapy provides optimal protection against lethal sepsis in a biodefense model of human melioidosis

The Gram-negative bacterium Burkholderia pseudomallei is the causative agent of melioidosis, a major cause of lethal sepsis and morbidity in endemic areas of Southeast Asia and a potential bioterrorism threat. We have used susceptible BALB/c mice to evaluate the potential of targeting vaccination and generic immunotherapy to the lung for optimal protection against respiratory challenge. Intranasal vaccination with live attenuated B. pseudomallei increased survival and induced interferon-γ-secreting T cells in the lung. Intranasal delivery of CpG oligodeoxynucleotides also provided significant protection; however, combining preexposure vaccination with CpG treatment at the time of infection or up to 18 hours after infection, provided significantly greater protection than either treatment alone. This combination prolonged survival, decreased bacterial loads by >1000-fold, and delayed the onset of sepsis. This novel approach may be applicable to other potential biodefense agents for which existing countermeasures are not fully effective.

Mucosal immunization with liposome-nucleic acid adjuvants generates effective humoral and cellular immunity

Development of effective new mucosal vaccine adjuvants has become a priority with the increase in emerging viral and bacterial pathogens. We previously reported that cationic liposomes complexed with non-coding plasmid DNA (CLDC) were effective parenteral vaccine adjuvants. However, little is known regarding the ability of liposome-nucleic acid complexes to function as mucosal vaccine adjuvants, or the nature of the mucosal immune responses elicited by mucosal liposome-nucleic acid adjuvants. To address these questions, antibody and T cell responses were assessed in mice following intranasal immunization with CLDC-adjuvanted vaccines. The effects of CLDC adjuvant on antigen uptake, trafficking, and cytokine responses in the airways and draining lymph nodes were also assessed. We found that mucosal immunization with CLDC-adjuvanted vaccines effectively generated potent mucosal IgA antibody responses, as well as systemic IgG responses. Notably, mucosal immunization with CLDC adjuvant was very effective in generating strong and sustained antigen-specific CD8(+) T cell responses in the airways of mice. Mucosal administration of CLDC vaccines also induced efficient uptake of antigen by DCs within the mediastinal lymph nodes. Finally, a killed bacterial vaccine adjuvanted with CLDC induced significant protection from lethal pulmonary challenge with Burkholderia pseudomallei. These findings suggest that liposome-nucleic acid adjuvants represent a promising new class of mucosal adjuvants for non-replicating vaccines, with notable efficiency at eliciting both humoral and cellular immune responses following intranasal administration.

Evaluation of surrogate animal models of melioidosis

Burkholderia pseudomallei is the Gram-negative bacterial pathogen responsible for the disease melioidosis. B. pseudomallei establishes disease in susceptible individuals through multiple routes of infection, all of which may proceed to a septicemic disease associated with a high mortality rate. B. pseudomallei opportunistically infects humans and a wide range of animals directly from the environment, and modeling of experimental melioidosis has been conducted in numerous biologically relevant models including mammalian and invertebrate hosts. This review seeks to summarize published findings related to established animal models of melioidosis, with an aim to compare and contrast the virulence of B. pseudomallei in these models. The effect of the route of delivery on disease is also discussed for intravenous, intraperitoneal, subcutaneous, intranasal, aerosol, oral, and intratracheal infection methodologies, with a particular focus on how they relate to modeling clinical melioidosis. The importance of the translational validity of the animal models used in B. pseudomallei research is highlighted as these studies have become increasingly therapeutic in nature.

Present and future therapeutic strategies for melioidosis and glanders

Burkholderia pseudomallei and Burkholderia mallei are the causative agents of melioidosis and glanders, respectively. Both Gram-negative pathogens are endemic in many parts of the world. Although natural acquisition of these pathogens is rare in the majority of countries, these bacteria have recently gained much interest because of their potential as bioterrorism agents. In modern times, their potential destructive impact on public health has escalated owing to the ability of these pathogens to cause opportunistic infections in diabetic and perhaps otherwise immunocompromised people, two growing populations worldwide. For both pathogens, severe infection in humans carries a high mortality rate, both species are recalcitrant to antibiotic therapy - B. pseudomallei more so than B. mallei - and no licensed vaccine exists for either prophylactic or therapeutic use. The potential malicious use of these organisms has accelerated the investigation of new ways to prevent and to treat the diseases. The availability of several B. pseudomallei and B. mallei genome sequences has greatly facilitated target identification and development of new therapeutics. This review provides a compilation of literature covering studies in antimelioidosis and antiglanders antimicrobial drug discovery, with a particular focus on potential novel therapeutic approaches to combat these diseases.