small molecules

2026-09-03 | Severe co-infection with influenza A virus H3N2 and community-acquired methicillin-susceptible Staphylococcus aureus in a child presenting with septic shock, acute respiratory distress syndrome, and necrotizing pneumonia: a rare case report.

Influenza co-infection with Staphylococcus aureus (S. aureus) can cause rapidly fatal necrotizing pneumonia, septic shock, and acute respiratory distress syndrome (ARDS) in children. Although methicillin-resistant S. aureus is often highlighted, community-acquired methicillin-susceptible S. aureus (CA-MSSA) can also produce equally severe disease. We report an 8-year-4-month-old male with influenza A (H3N2) who developed septic shock and refractory hypoxemia, requiring immediate intubation. Due to persisting respiratory failure despite maximal ventilation, veno-venous extracorporeal membrane oxygenation (VV-ECMO) was initiated on day 1. Metagenomic next-generation sequencing identified S. aureus as the dominant pathogen, and bronchoalveolar lavage fluid culture later confirmed MSSA. After vancomycin failed clinically, the regimen was switched to linezolid. However, on day 15 of linezolid therapy, the patient developed severe linezolid-induced lactic acidosis (LILA), which resolved within 3 days of stopping the drug. The clinical course was further complicated by pneumothorax and multidrug-resistant organism superinfections. After 54 days of intensive care, the patient was discharged in good condition. This case underscores that during influenza seasons, early empirical anti-staphylococcal therapy should be considered in children with rapidly progressive pneumonia and shock, even when CA-MSSA is suspected. Additionally, routine lactate monitoring is critical during linezolid therapy to enable prompt recognition and management of life-threatening LILA.

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2026-03-02 | Necrotizing Pneumonia in an Elderly Patient With Chronic Obstructive Pulmonary Disease (COPD): A Case Report.

Necrotizing pneumonia (NP) is a severe complication of bacterial pneumonia, characterized by progressive lung necrosis and cavitation. Although advances in imaging and supportive care have improved outcomes, NP remains difficult to manage due to poor antibiotic penetration, frequent polymicrobial infection, and the lack of standardized treatment protocols. An 85-year-old man with chronic obstructive pulmonary disease (COPD) (Global Initiative for Obstructive Lung Disease (GOLD) group C) and a 40-pack-year former smoking history, managed with long-acting beta-agonist/long-acting muscarinic antagonist (LABA/LAMA), was admitted with acute dyspnea and productive cough. Imaging showed left-sided pneumonia, and methicillin-sensitive Staphylococcus aureus (MSSA) was isolated. Amoxicillin-clavulanate led to transient improvement, but recurrent fever, worsening hypoxemia, and new cavitary lesions developed. Antimicrobial therapy was broadened to piperacillin-tazobactam, vancomycin, and voriconazole, without clinical stabilization. After empiric meropenem, the patient improved, completed 21 days of treatment, and fully recovered. However, without microbiologic confirmation, a direct causal link to meropenem cannot be established. This case highlights the diagnostic and therapeutic challenges of necrotizing pneumonia in elderly COPD patients, particularly when differentiation between progression, relapse, or superinfection is hampered by inconclusive microbiological findings. Although clinical improvement followed escalation to meropenem, the evidence does not permit attribution of recovery solely to this intervention. These findings reinforce the need for frequent reassessment, individualized treatment strategies, and caution in generalizing therapeutic recommendations from individual case reports. Early identification of necrotizing complications and timely modification of antimicrobial therapy are critical. Broad-spectrum antibiotics, including carbapenems, should be reserved for cases with compelling clinical or microbiologic evidence of multidrug resistance, rather than being used routinely based on isolated case experiences.

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2026-02-01 | Two-case cluster of rapidly progressive influenza B and Staphylococcus aureus pneumonia with one death.

To report a cluster of two epidemiologically linked construction workers with fulminant necrotizing pneumonia associated with co-infection by Panton-Valentine leukocidin (PVL)-positive methicillin-susceptible Staphylococcus aureus (MSSA) and influenza B virus. Clinical characteristics, imaging findings, and microbiological results were retrospectively reviewed. Metagenomic next-generation sequencing (mNGS) was performed on sputum and bronchoalveolar lavage fluid after conventional diagnostic tests failed to identify the causative pathogens. Following shared occupational exposure, both patients developed severe pneumonia. One patient experienced rapid progression and died. For the second patient, mNGS successfully identified co-infection with PVL-positive sequence type 22 MSSA and influenza B virus, prompting a timely shift to targeted antimicrobial therapy that led to survival after prolonged intensive care. This report demonstrates the extreme virulence of PVL-positive MSSA-influenza co-infection, highlights the diagnostic value of mNGS in severe treatment-refractory pneumonia, and emphasizes the need for effective respiratory protection in high-risk occupational environments.

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2026-01-28 | Evaluation of lawsone as a potential inhibitor of Staphylococcus aureus efflux pump mediated drugs resistance: An in-vitro and in-silico study.

Staphylococcus aureus (S. aureus) is a causative agent of a wide range of infections such as staphylococcal scalded skin syndrome, toxic shock syndrome, necrotizing pneumonia, endocarditis, and osteomyelitis, posing a significant challenge in clinical management. This study explores the antibacterial potential of lawsone on S. aureus using experimental and computational methods. The minimum inhibitory concentration (MIC) of lawsone (alone and in combination with erythromycin, tetracycline, norfloxacin and ciprofloxacin) on 8 clinical multi-drug resistant S. aureus was evaluated in vitro. The ability of lawsone to modulate antibiotic susceptibility was also determined. Molecular docking was carried out to investigate the binding affinities between lawsone and five efflux pumps (EPP) (NorA, NorB, MsrA, SepA, and MefA) and a ribosomal protection protein (TetM) implicated in S. aureus drug resistance. Furthermore, molecular dynamics simulations (MDS) were performed to assess the stability of the protein-ligand complexes throughout the 100 ns simulation period. In addition, the physicochemical properties, drug-likeness, and toxicity of the lawsone were predicted. Lawsone showed synergistic effects with erythromycin, tetracycline, norfloxacin, and ciprofloxacin, as indicated by the modulation factors (MF) ranging from 2 to > 16. Notably, the strain SA383 showed MF values of > 8 for two antibiotics (ciprofloxacin and erythromycin), and > 16 for norfloxacin. Molecular docking revealed strong binding affinities between lawsone and the evaluated S. aureus drug resistant proteins. The MDS confirmed the stability of the lawsone-protein complexes over 100 ns simulation period, supporting its potential as an efflux pump inhibitor (EPI). ADMET profiling of lawsone demonstrated favorable drug-likeness, pharmacokinetics, and low toxicity. Lawsone does not inhibit major cytochrome P450 enzymes. Toxicity predictions also showed no significant risks of carcinogenicity or immunotoxicity, but potential mutagenicity and nephrotoxicity which require further study. Lawsone also exhibits no predicted activity on androgen receptors, aromatase, or GABA receptors, indicating minimal hormonal disruption. These findings highlight lawsone as a promising candidate for the development of a new EPI candidate, particularly against antibiotic-resistant S. aureus.

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2026-01-22 | A case of necrotizing pneumonia leading to respiratory failure and tracheostomy.

Necrotizing pneumonia is a severe lung infection characterized by pulmonary necrosis and high mortality rates of up to 50 %. It is typically caused by toxin-producing pathogens, such as Staphylococcus aureus and Klebsiella pneumoniae. Limited guidelines exist for its management, making its treatment challenging. Case report: We discuss a case of a 58-year-old Malay woman with no significant comorbidity but developed necrotizing pneumonia. The diagnosis was confirmed using computed tomography (CT) of the thorax. Treatment with carbapenem, oxazolidinone and corticosteroid led to significant recovery. Conclusion: To date, no specific anti-inflammatory treatments exist for severe necrotizing pneumonia. Since systemic inflammation and multi-organ failure drive mortality, management focuses on supportive care aimed at maintaining oxygenation and hemodynamic stability to improve outcomes in critically ill patients.

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proteins

2025-02-21 | Therapeutic efficacy of LysGH15 against necrotising pneumonia caused by Staphylococcus aureus in a rabbit model.

Staphylococcus aureus (S. aureus) is one of the most important zoonotic pathogens and can be transmitted to humans through the meat diet routes, causing necrotising pneumonia. This study investigated the therapeutic effect of bacteriophage lysin LysGH15 on necrotising pneumonia in rabbit model caused by S. aureus. In the in vitro experiments, 50 μg/mL LysGH15 not only significantly reduced the viable count (approximately 3.24 × 106 CFU/g) of chicken meat stored at 4°C for 48 h but also effectively reduced the viable count of chicken meat thawed at 4°C and 30°C, with reductions of approximately 1.42 × 106 CFU/g and 2.78 × 106 CFU/g, respectively. In the in vivo experiments, a single intranasal administration of 300 μg/rabbit increased the survival rate of rabbits to 60%. At 72 h postinfection, the number of bacteria in the lung tissues of the rabbits treated with LysGH15 was 7 × 104 CFU/g, which was significantly lower than that in the lung tissues of rabbits treated with PBS (7.76 × 106 CFU/g) or linezolid (6.38 × 105 CFU/g). In addition, LysGH15 treatment alleviated lung tissue damage in infected rabbits and significantly reduced the levels of Panton-Valentine leukocidin (PVL), alpha-toxin (Hla), and the cytokines IFN-γ, TNF-α, and IL-8 in their lung tissues, similar to those in rabbits treated with linezolid. These results suggest that LysGH15 has the potential to be used as a novel antimicrobial agent for the treatment of necrotising pneumonia caused by S. aureus.

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2023-10-02 | Nuclease activity and protein A release of Staphylococcus aureus clinical isolates determine the virulence in a murine model of acute lung infection

Staphylococcus aureus is a common cause of hospital-acquired pneumonia associated with high mortality. Adequate clinical treatment is impeded by increasing occurrence of antibiotic resistances. Understanding the underlying mechanisms of its virulence during infections is a prerequisite to finding alternative treatments. Here, we demonstrated that an increased nuclease activity of a S. aureus isolate from a person with cystic fibrosis confers a growth advantage in a model of acute lung infection compared to the isogenic strain with low nuclease activity. Comparing these CF-isolates with a common MRSA-USA300 strain with similarly high nuclease activity but significantly elevated levels of Staphylococcal Protein A (SpA) revealed that infection with USA300 resulted in a significantly increased bacterial burden in a model of murine lung infection. Replenishment with the cell wall-bound SpA of S. aureus , which can also be secreted into the environment and binds to tumor necrosis factor receptor -1 (TNFR-1) to the CF-isolates abrogated these differences. In vitro experiments confirmed significant differences in spa -expression between USA300 compared to CF-isolates, thereby influencing TNFR-1 shedding, L-selectin shedding, and production of reactive oxygen species through activation of ADAM17.

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2023-08-14 | Antimicrobial Peptides Demonstrate Activity against Resistant Bacterial Pathogens

The antimicrobial resistance crisis is an ongoing major threat to public health safety. Low- and middle-income countries are particularly susceptible to higher fatality rates and the economic impact of antimicrobial resistance (AMR). As an increasing number of pathogens emerge with multi- and pan-drug resistance to last-resort antibiotics, there is an urgent need to provide alternative antibacterial options to mitigate disease transmission, morbidity, and mortality. As identified by the World Health Organization (WHO), critically important pathogens such as Klebsiella and Pseudomonas species are becoming resistant to last-resort antibiotics including colistin while being frequently isolated from clinical cases of infection. Antimicrobial peptides are potent amino acid sequences produced by many life forms from prokaryotic, fungal, plant, to animal species. These peptides have many advantages, including their multi-hit mode of action, potency, and rapid onset of action with low levels of resistance being evident. These innate defense mechanisms also have an immune-stimulating action among other activities in vivo, thus making them ideal therapeutic options. Large-scale production and formulation issues (pharmacokinetics, pharmacodynamics), high cost, and protease instability hinder their mass production and limit their clinical application. This review outlines the potential of these peptides to act as therapeutic agents in the treatment of multidrug-resistant infections considering the mode of action, resistance, and formulation aspects. Clinically relevant Gram-positive and Gram-negative pathogens are highlighted according to the WHO priority pathogen list.

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2022-03-07 | Antibacterial activities of two potential peptides extracted from Polistes wattii Cameron, 1900 (Vespidae: Polistinae) wasp venom collected at Eastern Province, Saudi Arabia

Alternatives of conventional antibiotics have become an urgent need to control drug-resistant bacteria. Therefore, search for new antibacterial agents has become a trend in several microbiological and pharmaceutical scientific works. Insects, one of the most successful and evolved species on earth is known to be an effective natural source of several medically useful chemicals including antibacterial agents. There is considerable evidence of using wasp venom against medical ailments in several parts of the world. In this work venom from Polistes wattii Cameron, 1900 collected from Eastern Province, Saudi Arabia was evaluated for its antibacterial activities. Such activity was tested against four pathogenic bacteria: two-gram positive Staphylococcus aureus (ATCC 25923) and Streptococcus mutans (RCMB 017(1) ATCC 25175) and two gram-negative ( Salmonella typhimurium NCTC 12023 ATCC 14028 and Enterobacter cloacae (RCMB 001(1) ATCC 23355). Also, chemical characterization of wasp venom was done using HPLC and two isolated peptides were sequenced. The result indicates the potent anti-microbial effect of the venom against the four tested bacteria. The most sensitive bacteria were Staphylococcus aureus (ATCC 25923) and Streptococcus mutans (RCMB 017(1) ATCC 25175). The sequence of the two purified peptides indicates that they belong to mastoparan. The study results may pave way to use this wasp venom in future antibiotics especially in controlling skin infection by Staphylococcus aureus .

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2021-03-22 | Antimicrobial peptides-An alternative candidates to antibiotics against Staphylococcus aureus and its antibiotic-resistant strains

Staphylococcus aureus and its antibiotic-resistant strains are the cause of soft tissue infections representing some severe life-threatening infections. These situations have caused great concern for its treatment worldwide. Thus, the need to introduce new antibiotics or an alternative to antibiotics markedly increasing. Antimicrobial peptides (AMPs) have been shown to have various properties and uses in the biological system since their discovery. This review is based on the increasing concern for S. aureus, its resistant strains, the associated infections, pathogenicity, and the mechanism of resistance to antibiotics. Lastly, the overall significance of AMPs against S. aureus showed that they can be ideal candidates as an alternative to antibiotics with high potential for future therapeutics.

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vaccines

2022-05-24 | Synthetic Glycans to Improve Current Glycoconjugate Vaccines and Fight Antimicrobial Resistance

Antimicrobial resistance (AMR) is emerging as the next potential pandemic. Different microorganisms, including the bacteria Acinetobacter baumannii, Clostridioides difficile, Escherichia coli, Enterococcus faecium, Klebsiella pneumoniae, Neisseria gonorrhoeae, Pseudomonas aeruginosa, non-typhoidal Salmonella, and Staphylococcus aureus, and the fungus Candida auris, have been identified by the WHO and CDC as urgent or serious AMR threats. Others, such as group A and B Streptococci, are classified as concerning threats. Glycoconjugate vaccines have been demonstrated to be an efficacious and cost-effective measure to combat infections against Haemophilus influenzae, Neisseria meningitis, Streptococcus pneumoniae, and, more recently, Salmonella typhi. Recent times have seen enormous progress in methodologies for the assembly of complex glycans and glycoconjugates, with developments in synthetic, chemoenzymatic, and glycoengineering methodologies. This review analyzes the advancement of glycoconjugate vaccines based on synthetic carbohydrates to improve existing vaccines and identify novel candidates to combat AMR. Through this literature survey we built an overview of structure–immunogenicity relationships from available data and identify gaps and areas for further research to better exploit the peculiar role of carbohydrates as vaccine targets and create the next generation of synthetic carbohydrate-based vaccines.

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2022-04-01 | Staphylococcus aureus specific lung resident memory CD4+ Th1 cells attenuate the severity of influenza virus induced secondary bacterial pneumonia

Staphylococcus aureus is a major cause of severe pulmonary infections. The evolution of multi-drug resistant strains limits antibiotic treatment options. To date, all candidate vaccines tested have failed, highlighting the need for an increased understanding of the immunological requirements for effective S. aureus immunity. Using an S. aureus strain engineered to express a trackable CD4+ T cell epitope and a murine model of S. aureus pneumonia, we show strategies that lodge Th1 polarised bacterium specific CD4+ tissue resident memory T cells (Trm) in the lung can significantly attenuate the severity of S. aureus pneumonia. This contrasts natural infection of mice that fails to lodge CD4+ Trm cells along the respiratory tract or provide protection against re-infection, despite initially generating Th17 bacterium specific CD4+ T cell responses. Interestingly, lack of CD4+ Trm formation after natural infection in mice appears to be reflected in humans, where the frequency of S. aureus reactive CD4+ Trm cells in lung tissue is also low. Our findings reveal the protective capacity of S. aureus specific respiratory tract CD4+ Th1 polarised Trm cells and highlight the potential for targeting these cells in vaccines that aim to prevent the development of S. aureus pneumonia.

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2019-01-14 | Molecular epidemiology and expression of capsular polysaccharides in Staphylococcus aureus clinical isolates in the United States

Staphylococcus aureus capsular polysaccharides (CP) are important virulence factors under evaluation as vaccine antigens. Clinical S. aureus isolates have the biosynthetic capability to express either CP5 or CP8 and an understanding of the relationship between CP genotype/phenotype and S. aureus epidemiology is valuable. Using whole genome sequencing, the clonal relatedness and CP genotype were evaluated for disease-associated S. aureus isolates selected from the Tigecycline Evaluation and Surveillance Trial (T.E.S.T) to represent different geographic regions in the United States (US) during 2004 and 2009-10. Thirteen prominent clonal complexes (CC) were identified, with CC5, 8, 30 and 45 representing >80% of disease isolates. CC5 and CC8 isolates were CP type 5 and, CC30 and CC45 isolates were CP type 8. Representative isolates from prevalent CC were susceptible to in vitro opsonophagocytic killing elicited by anti-CP antibodies, demonstrating that susceptibility to opsonic killing is not linked to the genetic lineage. However, as not all S. aureus isolates may express CP, isolates representing the diversity of disease isolates were assessed for CP production. While approximately 35% of isolates (primarily CC8) did not express CP in vitro, CP expression could be clearly demonstrated in vivo for 77% of a subset of these isolates (n = 20) despite the presence of mutations within the capsule operon. CP expression in vivo was also confirmed indirectly by measuring an increase in CP specific antibodies in mice infected with CP5 or CP8 isolates. Detection of antigen expression in vivo in relevant disease states is important to support the inclusion of these antigens in vaccines. Our findings confirm the validity of CP as vaccine targets and the potential of CP-based vaccines to contribute to S. aureus disease prevention.

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2016-12-24 | Safety and immunogenicity of a recombinant Staphylococcus aureus α-toxoid and a recombinant Panton-Valentine leukocidin subunit, in healthy adults.

We conducted a randomized, double-blind, placebo-controlled dose-escalation study in healthy adults to evaluate the safety and immunogenicity of recombinant Staphylococcus aureus candidate vaccine antigens, recombinant α-toxoid (rAT) and a sub-unit of Panton-Valentine leukocidin (rLukS-PV). 176 subjects were enrolled and randomized within 1 of 11 treatment cohorts: monovalent rAT or rLukS-PV dosages of 10, 25, 50, and 100 μg; bivalent rAT:rLukS dosages of 10:10, 25:25, and 50:50 μg; and alum or saline placebo. All subjects were assessed at Days 0, 7, 14, 28, and 84. Subjects in the 50:50 μg bivalent cohort received a second injection on Day 84 and were assessed on Days 98 and 112. Incidence and severity of reactogenicity and adverse events (AEs) were compared. Geometric mean serum concentrations (GMC) and neutralizing activity of anti-rAT and anti-rLukS-PV IgG were assessed. Reactogenicity incidence was significantly higher in vaccine than placebo recipients (77% versus 55%, respectively; p = 0.006). However, 77% of reactogenicity events were mild and 19% were moderate in severity. The AE incidence and severity were similar between the cohorts. All monovalent and bivalent rAT dosages resulted in a significant increase in the anti-rAT IgG and anti- rLukS-PV GMCs between day 0 and 28 compared with placebo, and persisted through Day 84. Exploratory subgroup analyses suggested a higher GMC and neutralizing antibody titers for the 50 μg monovalent or bivalent rAT and rLukS-PV dose as compared to the other doses. No booster effect was observed after administration of the second dose. We conclude that the rAT and rLukS-PV vaccine formulations were well-tolerated and had a favorable immunogenicity profile, producing antibody with neutralizing activity through day 84. There was no benefit observed with a booster dose of the vaccine.

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2016-10-01 | Elucidating the anti-Staphylococcus aureus antibody response by immunoproteomics.

Staphylococcus aureus is a notorious pathogen both in‐ and outside hospitals as well as a frequent colonizer in healthy individuals. Immunoproteomics techniques have been employed to shed light on the human adaptive immune response to S. aureus in health and disease. Since priming of immune memory, a key property of the adaptive immune system, is the basis of successful vaccination, immunoproteomics holds promise for paving the way to an effective S. aureus vaccine.

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antibodies

2026-05-27 | Host Determinants of Toxicity and Inflammation: Learning from staphylococcal alpha-toxin

Staphylococcus aureus is a bacterium commonly found in humans. Approximately one-third of healthy adults carry this bacterium without becoming ill. However, S. aureus can cause infections with varying clinical manifestations. Most people develop only mild skin infections. In rare cases, life-threatening conditions such as necrotizing pneumonia or severe infections of the skin and soft tissues can occur. Why some people become seriously ill and others do not is not yet fully understood. An important factor in the disease caused by S. aureus is a toxin produced by the bacterium: α-toxin. This toxin creates small pores in the membrane of human cells, causing cells to be damaged or die. In this thesis, we investigated which variables contribute to how harmful this toxin is to human cells. We studied the molecular interaction between α-toxin and human cells and found that the toxin binds to an important and conserved component of the membrane protein ADAM10. In addition, we demonstrate that conditions within the body, such as the acidity (pH) of the environment, can strongly influence the activity of the toxin. Finally, we studied patients with a rare genetic defect in the OTULIN gene. These patients are, among other things, highly sensitive to the harmful effects of α-toxin and can consequently develop life-threatening infections. Our findings show that the severity of S. aureus infections is determined by both the bacterium and the host. The genetic makeup and environmental conditions within the body influence the sensitivity of human cells to substances produced by S. aureus. A better understanding of these interactions could contribute to more targeted treatments for severe bacterial infections in the future.

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2018-08-06 | Minimal physiologically-based pharmacokinetic modeling of DSTA4637A, A novel THIOMAB™ antibody antibiotic conjugate against Staphylococcus aureus, in a mouse model.

DSTA4637A, a THIOMAB™ antibody-antibiotic conjugate targeting Staphylococcus aureus, has shown promising bactericidal activity in a mouse model. DSTA4637A consists of a monoclonal anti-S. aureus antibody with an average of two rifalogue antibiotic molecules, dmDNA31, linked to its light chains. The goal of this study was to develop a minimal physiologically-based pharmacokinetic (mPBPK) model to characterize the pharmacokinetic (PK) properties of three analytes of DSTA4637A (i.e., total antibody, antibody-conjugated dmDNA31, and unconjugated dmDNA31) in mice, and to predict pharmacokinetics of DSTA4637A analytes in humans, as well as to provide an initial assessment for potential PK drug-drug interactions (DDI) in clinical trials via cross-species scaling of the mPBPK model. In the proposed model, selected organs, including heart, liver, and kidney, were connected anatomically with plasma and lymph flows. Mouse plasma and tissue concentrations of the three analytes of DSTA4637A were fitted simultaneously to estimate the PK parameters. Cross-species scaling of the model was performed by integrating allometric scaling and human physiological parameters. The final mPBPK model was able to successfully capture PK profiles of three DSTA4637A analytes in mouse plasma and in investigated organs. The model predicted a steady-state peak unbound dmDNA31 concentration lower than 5% of the IC50 of dmDNA31 towards cytochrome P450 following 100 mg/kg weekly intravenous dose, which suggests a low risk of PK DDI in humans for DSTA4637A with co-administered cytochrome P450 substrates. The proposed mPBPK modeling and cross-species scaling approaches provide valuable tools that facilitate the understanding and translation of DSTA4637A disposition from preclinical species to humans.

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2017-11-03 | Disarming Staphylococcus aureus from destroying human cells by simultaneously neutralizing six cytotoxins with two human monoclonal antibodies.

Pathogenesis of Staphylococcus aureus is increasingly recognized to be driven by powerful toxins. Staphylococcus aureus employs up to six pore-forming toxins to subvert the human host defense and to promote bacterial invasion: alpha-hemolysin that disrupts epithelial and endothelial barriers and five leukocidins that lyse phagocytes involved in bacterial clearance. Previously, we described two human monoclonal antibodies (mAbs), ASN-1 that neutralizes alpha-hemolysin and four leukocidins (LukSF-PV, LukED, HlgAB, HlgCB), and ASN-2 that inactivates the 5th leukocidin, LukGH. In this study we tested the individual and combined effects of ASN-1 and ASN-2 in multiple in vitro models employing relevant human target cells. We found that diverse S. aureus isolates with different genetic backgrounds (based on MLST- and spa-typing) and antibiotic sensitivity (both MRSA and MSSA) displayed greatly different cytotoxin expression patterns influenced by the type of growth medium used. Both mAbs were required to fully prevent the lysis of human neutrophils exposed to the mixture of recombinant cytotoxins or native toxins present in the culture supernatants of S. aureus isolates. Flow cytometry confirmed the protective effects of ASN-1 + ASN-2 (known as ASN100) on granulocytes, monocytes, NK-cells and T-lymphocytes. ASN-1 alone preserved the integrity of a 3D-primary culture of human tracheal/bronchial mucociliary epithelial tissue infected with S. aureus. We conclude that simultaneous inhibition of alpha-hemolysin and five leukocidins by ASN100 blocks cytolytic activity of S. aureus towards human target cells in vitro.

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2017-09-25 | Targeting Alpha Toxin To Mitigate Its Lethal Toxicity in Ferret and Rabbit Models of Staphylococcus aureus Necrotizing Pneumonia.

The role broad-spectrum antibiotics play in the spread of antimicrobial resistance, coupled with their effect on the healthy microbiome, has led to advances in pathogen-specific approaches for the prevention or treatment of serious bacterial infections. One approach in clinical testing is passive immunization with a monoclonal antibody (MAb) targeting alpha toxin for the prevention or treatment of Staphylococcus aureus pneumonia. Passive immunization with the human anti-alpha toxin MAb, MEDI4893*, has been shown to improve disease outcome in murine S. aureus pneumonia models. The species specificity of some S. aureus toxins necessitates testing anti-S. aureus therapeutics in alternate species. We developed a necrotizing pneumonia model in ferrets and utilized an existing rabbit pneumonia model to characterize MEDI4893* protective activity in species other than mice. MEDI4893* prophylaxis reduced disease severity in ferret and rabbit pneumonia models against both community-associated methicillin-resistant S. aureus (MRSA) and hospital-associated MRSA strains. In addition, adjunctive treatment of MEDI4893* with either vancomycin or linezolid provided enhanced protection in rabbits relative to the antibiotics alone. These results confirm that MEDI4893 is a promising candidate for immunotherapy against S. aureus pneumonia.

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2016-10-28 | Enterotoxin Gene Cluster-Encoded SEI and SElN from Staphylococcus aureus Isolates are Crucial for the Induction of Human Blood Cell Proliferation and Pathogenicity in Rabbits

Among the toxin family of bacterial superantigens, the six members of the enterotoxin gene cluster (egc) seem to have unusual characteristics. They are present in the majority of Staphylococcus aureus strains, but their role in disease remains uncertain. We assessed secretion levels, immunogenicity, and toxicity of native and recombinant egc proteins. After having developed enzyme-linked immunosorbent assays, we found different quantities of egc proteins secreted by bacterial isolates. Supernatants induced proliferation of human peripheral blood mononuclear cells. However, purified recombinant egc proteins were shown to have differing superantigenicity potentials. Immunization with identical amounts of all members of egc, and the prominent toxic agent SEB, resulted in neutralizing antisera. Two egc proteins, SEI and SElN, were found to play a predominant role within the cluster. Both displayed the highest potential to activate blood cells, and were essential to be neutralized in supernatants. The application of a supernatant of a strain bearing only egc was sufficient for a lethal outcome in a rabbit model. Again, neutralization of SEI and SElN led to the survival of all tested animals. Finally, nanogram amounts of purified rSEI and rSElN led to lethality in vivo, pointing out the importance of both as virulence determinants among egc superantigens.

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other

2023-02-28 | Time-Course Transcriptome Analysis of the Lungs of Mice Challenged with Aerosols of Methicillin-Resistant Staphylococcus aureus USA300 Clone Reveals Inflammatory Balance.

USA300, a dominant clone of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), is circulating globally and can cause necrotizing pneumonia with high morbidity and mortality. To further reveal the host anti-MRSA infection immune response, we established a mouse model of acute primary MRSA pneumonia challenged with aerosols of the USA300 clone. A time-course transcriptome analysis of the lungs collected at 0, 12, 24, 48 and 96 h post-infection (hpi) was conducted using RNA sequencing (RNA-seq) and multiple bioinformatic analysis methods. The change trend of histopathology and five innate immune cell (neutrophils, mononuclear cells, eosinophils, macrophages, DC cells) proportions in the lungs after infection was also examined. We observed a distinct acute pulmonary recovery process. A rapid initiation period of inflammation was present at 12 hpi, during which the IL-17 pathway dominantly mediated inflammation and immune defense. The main stages of host inflammatory response occurred at 24 and 48 hpi, and the regulation of interferon activation and macrophage polarization played an important role in the control of inflammatory balance at this stage. At 96 hpi, cellular proliferation processes associated with host repair were observed, as well as adaptive immunity and complement system responses involving C1q molecules. More importantly, the data provide new insight into and identify potential functional genes involved in the checks and balances occurring between host anti-inflammatory and proinflammatory responses. To the best of our knowledge, this is the first study to investigate transcriptional responses throughout the inflammatory recovery process in the lungs after MRSA infection. Our study uncovers valuable research targets for key regulatory mechanisms underlying the pathogenesis of MRSA lung infections, which may help to develop novel treatment strategies for MRSA pneumonia.

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2012-08-24 | CodY deletion enhances in vivo virulence of community-associated methicillin-resistant Staphylococcus aureus clone USA300.

The Staphylococcus aureus global regulator CodY responds to nutrient availability by controlling the expression of target genes. In vitro, CodY represses the transcription of virulence genes, but it is not known if CodY also represses virulence in vivo. The dominant community-associated methicillin-resistant S. aureus (CA-MRSA) clone, USA300, is hypervirulent and has increased transcription of global regulators and virulence genes; these features are reminiscent of a strain defective in CodY. Sequence analysis revealed, however, that the codY genes of USA300 and other sequenced S. aureus isolates are not significantly different from the codY genes in strains known to have active CodY. codY was expressed in USA300, as well as in other pulsotypes assessed. Deletion of codY from a USA300 clinical isolate resulted in modestly increased expression of the global regulators agr and saeRS, as well as the gene encoding the toxin alpha-hemolysin (hla). A substantial increase (>30-fold) in expression of the lukF-PV gene, encoding part of the Panton-Valentine leukocidin (PVL), was observed in the codY mutant. All of these expression differences were reversed by complementation with a functional codY gene. Moreover, purified CodY protein bound upstream of the lukSF-PV operon, indicating that CodY directly represses expression of lukSF-PV. Deletion of codY increased the virulence of USA300 in necrotizing pneumonia and skin infection. Interestingly, deletion of lukSF-PV from the codY mutant did not attenuate virulence, indicating that the hypervirulence of the codY mutant was not explained by overexpression of PVL. These results demonstrate that CodY is active in USA300 and that CodY-mediated repression restrains the virulence of USA300.

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2006-12-10 | Repression of Staphylococcus aureus SrrAB using inducible antisense srrA alters growth and virulence factor transcript levels.

Our laboratory has previously identified the staphylococcal respiratory response (SrrAB), a Staphylococcus aureus two-component system that acts in the global regulation of virulence factors. In strain RN4220, SrrAB downregulated production of agr RNAIII, protein A, and TSST-1, particularly under low-oxygen conditions. Work by another group showed that SrrAB regulates energy metabolism genes and indicated that SrrAB may regulate energy transduction in response to changes in oxygen availability. In this study we investigate the role of SrrAB in regulating RNAIII, tst, spa, icaR, and icaA in a clinical isolate of S. aureus, MN8. We employ an inducible antisense vector, pYJY4, in order to repress transcription of srrAB. Transcript levels were assessed by reverse transcription followed by quantitative PCR. Repression of srrAB in rich media under aerobic growth conditions shows that SrrAB is required for expression of tst, spa, and icaR transcripts at wild-type levels. Comparisons made between rich media under aerobic conditions vs low-oxygen conditions show that srrAB transcript levels are not altered by oxygen alone. Previous studies performed on strain RN4220 under low-oxygen conditions indicate that SrrAB represses tst and spa transcript when the amount of oxygen is limited. We propose that, under aerobic conditions, SrrAB enhances the levels of tst, spa, and icaR, while under low-oxygen conditions, SrrAB decreases the levels of these three transcripts.

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