ESKAPE bacterial products as modulators of natural killer cell function

Uncommon Gram-Negative Opportunists as Drivers of Cancer-Related Immunomodulation: The Virulence Machinery of Aeromonas, Shewanella, and Morganella Species

Immunosuppression and tissue destruction related to cancer provide a niche of permissible colonization by opportunistic bacteria, although the role of uncommon gram-negative pathogens in tumor-associated immune modulation has not been studied in detail. New findings point to Aeromonas, Shewanella, and Morganella organisms that were historically considered either environmental or low-virulence provirulence organisms as potential active mediators of cancer-related immunomodulation by having highly complex virulence systems. These bacteria have a repertoire of pathogenic determinants such as type III and type VI secretion systems, iron acquisition mechanisms, endotoxin reorganization, biofilm formation, and outer membrane vesicle release that allow them to withstand antagonistic tumor microenvironment and a direct contact with host immune pathways. Along with the cancer environment, these opportunists can contribute to immune dysregulation through cytokine profile distortion, phagocytic dysfunction, persistent inflammation, and immune evasion. Their redox-adaptive capacities and metabolic flexibility also favor their survival in hypoxic environments, nutrient-scarcity and oxidative stress, which are the hallmarks of solid tumors. Most importantly, the communication between these bacteria and tumor-related immune cells, including macrophages and neutrophils can strengthen pro-tumorigenic inflammation and suppress efficient antitumor immunity. Simultaneously, antimicrobial resistance characteristics and stress-regulated virulence determinants increase their clinical usefulness in immunocompromised cancer patients. The current review has identified the mechanistic roles of the Aeromonas, Shewanella and Morganella species as unorthodox yet biologically important mediators of immune homeostasis to cancer. Their virulence mechanisms and contact with the host can reveal new biomarkers of infection-mediated tumor pathogenesis and be useful in combination therapy with microbial-specific factors and immune dysfunction in cancer management.

Exploiting classical virulence factor: staphylococcal protein a in immunotherapy and immunodiagnosis

An extensive insight is provided into the dual role of SpA as a virulence factor in S. aureus pathogenesis and its widespread application in biotechnology, including its vital role in affinity purification of polyclonal and monoclonal antibodies.

Identification of SKI-II as a host-protective immunomodulator against Staphylococcus aureus infection

ABSTRACT Antibiotic resistance threatens the effectiveness of conventional antimicrobial agents, underscoring the need for host-directed therapies that enhance immune defense. Here, we present a cross-species discovery pipeline that couples a Caenorhabditis elegans–Staphylococcus aureus liquid-based infection screen with mammalian mechanistic validation to identify small-molecule immunomodulators. Using six C. elegans innate immunity reporter strains, we identified a known small molecule, SKI-II, as a previously unrecognized host-protective compound that activates the C. elegans SKN-1/Nrf2 oxidative-stress pathway. In mouse RAW264.7 macrophages, SKI-II binds to the ATPase pocket of VCP (Valosin-Containing Protein), activating the PERK-dependent (Protein kinase R [PKR]-like Endoplasmic Reticulum Kinase) Nrf2 signaling regulation axis that reduces the levels of pathogenic ROS (reactive oxygen species). SKI-II treatment also promotes macrophage M1 polarization and a mitochondrial metabolic shift. This work identifies VCP as a druggable node for host-directed immunomodulation and highlights SKI-II as a prototype small molecule that boosts host tolerance to infection, thereby validating our C. elegans-based screening platform for discovering immunomodulators active in mammalian systems. IMPORTANCE Enhancing host immunity is a promising strategy to combat S. aureus infection, particularly multidrug-resistant strains. In this study, we applied a C. elegans liquid-based infection screening model to identify the immunomodulatory compound SKI-II. We demonstrate that SKI-II protects against S. aureus infection in both nematodes and mouse macrophages by regulating host oxidative stress pathways rather than directly targeting the pathogen. We reveal a regulatory circuit in which VCP functions as a central node controlling cellular ROS responses and activating the downstream PERK-dependent Nrf2 antioxidant signaling pathway. These findings advance our understanding of host cellular responses to bacterial infection and highlight VCP as a druggable target for host-directed therapeutic strategies against infectious diseases. Enhancing host immunity is a promising strategy to combat S. aureus infection, particularly multidrug-resistant strains. In this study, we applied a C. elegans liquid-based infection screening model to identify the immunomodulatory compound SKI-II. We demonstrate that SKI-II protects against S. aureus infection in both nematodes and mouse macrophages by regulating host oxidative stress pathways rather than directly targeting the pathogen. We reveal a regulatory circuit in which VCP functions as a central node controlling cellular ROS responses and activating the downstream PERK-dependent Nrf2 antioxidant signaling pathway. These findings advance our understanding of host cellular responses to bacterial infection and highlight VCP as a druggable target for host-directed therapeutic strategies against infectious diseases.

Will It Be Possible in the Future to Target Innate Immunity Against Staphylococcus aureus Using Resident Microbiota and Plant Extracts?

Staphylococcus aureus remains a major cause of hospital‐ and community‐acquired infections, successfully evading host defense mechanisms and escaping proposed vaccination strategies. The effective response of professional phagocytes is crucial in limiting the spread, tissue invasion, and subsequent infection by S. aureus. However, direct stimulation of innate immunity with S. aureus antigens is too risky due to their strong proinflammatory properties. Therefore, this study aimed to test the hypothesis that plant extracts trigger the gentle release of staphylococcal bioactive components that can modulate innate immunity. This strategy was tested in vitro; however, it may have future applications by employing the resident microbiota and dietary supplements containing plant extracts. In this study, the THP‐1‐derived macrophages were exposed to the supernatants of planktonic and biofilm S. aureus cultures pretreated with Viburnum opulus L. bark and fruit extracts. Vancomycin (VAN) and chlorogenic acid (ChA), used at subinhibitory concentrations, were included for comparison regarding the release of S. aureus active components. The cells were also exposed to purified bacterial cell wall components. Various elements of the immune response were assessed, including surface expression of cluster of differentiation (CD11c, CD206) via flow cytometry, cytokine production (tumor necrosis factor‐alpha [TNF‐α] and interleukin 10 [IL‐10]) via ELISA, and S. aureus phagocytosis and intracellular killing using fluorescein isothiocyanate (FITC)‐labeled bacteria and Alamar Blue staining. It was demonstrated that both supernatants from planktonic and biofilm S. aureus cultures pre‐exposed to V. opulus extracts, as well as the bacterial cell wall components themselves, significantly increased TNF‐α and IL‐10 production by THP‐1‐derived macrophages and visibly reduced intracellular multiplication of engulfed S. aureus. The lack of changes in the surface CD marker expression may be a limitation of the model used (phorbol‐12‐myristate‐13‐acetate [PMA]‐differentiated THP‐1) rather than the phenomenon itself, that leads to a “ceiling effect”. To sum up, the study presents V. opulus extracts as the triggers to release bioactive components from S. aureus cells, able to target innate immunity against staphylococci, which may be used in the future.

Targeted delivery of peptidoglycan hydrolases (PGH) via engineered extracellular vesicles (EVs) to clear intracellular bacterial infections

Bacterial infectious diseases remain a major global health threat due to increasing antibiotic resistance. Further complicating effective treatment, some pathogens such as Staphylococcus aureus persist within host cells. Peptidoglycan hydrolases (PGHs), including bacteriophage-derived endolysins, represent a promising class of novel antimicrobials due to their rapid bacteriolytic activity and low risk of resistance emergence. However, their clinical application is limited by an unfavourable PK profile and inefficient delivery into infected host cells. Here, we engineered extracellular vesicles (EVs) for the targeted, intracellular delivery of GH15, a novel endolysin against S. aureus. GH15-loaded EVs, functionalized with antibodies targeting αvβ3 integrin on bacterially infected cells, efficiently delivered GH15 into S. aureus-positive endothelial cells and macrophages in vitro and eliminated intracellular bacteria. In addition, GH15-loaded EVs promoted the clearance of intracellular bacteria in macrophages of infected zebrafish larvae in vivo. Our findings establish EVs as effective vehicles for intracellular delivery of antimicrobial enzymes and highlight their potential for the treatment of intracellular bacterial infections.

Lactic acid bacteria-derived biosurfactants: emerging strategies for biofilm control, virulence attenuation, and food safety