Conserved moonlighting protein pyruvate dehydrogenase induces robust protection against Staphylococcus aureus infection 2248909

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.

Characterization and therapeutic potential of two Kayvirus phages against methicillin-resistant S. aureus in a rat myositis model.

A plasmid-associated immunoglobulin-binding protein in Acinetobacter baumannii

Summary Background Acinetobacter baumannii is a critical global health threat due to multidrug resistance and high mortality. Although antimicrobial resistance mechanisms are well characterised, the virulence determinants that drive severe infections remain poorly understood. Methods We screened 89 carbapenem-resistant clinical isolates of A. baumannii for virulence in animal infection models and combined comparative genomics with functional assays to identify virulence factors. An immunoglobulin-binding protein from A. baumannii (ImbA) encoded on the type D plasmid was selected and characterised. Protein–immunoglobulin interactions were analysed by pull-down and biolayer interferometry. Additional ImbA inhibition of IgG–Fcγ receptor binding by flow cytometry were tested. Protective efficacy was evaluated in mice using vaccination or anti-ImbA antibodies. Findings A type D plasmid was consistently linked to high virulence in clinical isolates. The deletion of plasmid-encoded ImbA attenuated virulence. ImbA bound murine IgA and IgG with high affinity. The binding to the Fc region of IgG disrupted IgG–Fcγ receptor interactions. Vaccination with recombinant ImbA improved survival and reduced bacterial dissemination in female mice with anti-ImbA antibodies partially protecting against lethal infection. Bacterial burdens in the blood were reduced in treated groups. Interpretation Our study demonstrates ImbA as an unrecognised plasmid-encoded virulence factor in A. baumannii. By intercepting host immunoglobulins, ImbA drives immune evasion and hypervirulence. Blocking ImbA by vaccination and antibody therapy restored host defence and improved outcomes in female mice, highlighting ImbA as a non-antibiotic therapeutic target with potential against multidrug-resistant A. baumannii. Funding Bio&Medical Technology Development Program of the National Research Foundation (NRF), funded by the Korean government (MSIT) (No. RS-2023-00219213); Korea Research Institute of Bioscience and Biotechnology (KRIBB) Research Initiative Program.

Gene-Specific Rewiring of Type I Interferon Responses by Staphylococcus aureus 2329926

Staphylococcus aureus is a Gram-positive pathogen that is a major cause of soft tissue and bloodstream infections in humans. Previous studies have shown that S. aureus triggers myeloid cell-driven innate immune activation including inflammatory signaling and type I interferon (IFN) responses; however, the role type I IFNs remains controversial. Primary human CD14+ monocytes were purified from PBMCs of healthy donors using anti-CD14 magnetic beads. Monocytes were infected with various doses of S. aureus and harvested for RT-qPCR, Western blotting, and integrated bulk RNA sequencing, ATAC-seq and CUT&RUN. We observed a dose-dependent dichotomous regulation of the IFN response, which was induced by low doses and suppressed at high doses of S. aureus. Only a subset of interferon-stimulated genes (ISGs) was induced despite intact IFNβ production following S. aureus infection. Intriguingly, S. aureus selectively abrogated the activation and nuclear translocation of STAT1, while activation and nuclear translocation of the other ISGF3 components STAT2 and IRF9 were preserved. Furthermore, RNA profiling revealed a disparate regulation of gene expression, with a distinct subset of genes exhibiting significantly enhanced expression upon combined S. aureus and IFNβ treatment. Epigenomic profiling showed a complete repression of chromatin accessibility as well as STAT1 binding at a subset of ISG loci upon S. aureus infection, whereas another subset of ISGs displayed increased chromatin accessibility and transcriptional activation upon infection. Our findings suggest that S. aureus alters activation of the canonical type I IFN-mediated Jak-STAT pathway through suppression of STAT1 activation and altering chromatin remodeling . This change in signaling is associated with gene-specific reprogramming of the type I IFN response by S. aureus that may alter the host response to this pathogen in a context-dependent manner and contribute to difficulty in clearing S. aureus infection. n/a Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)

Oral delivery of recombinant Bacillus subtilis expressing mSEB reduces intestinal Staphylococcus aureus colonization.

BACKGROUND S. aureus intestinal colonization elevates infection risk, underscoring decolonization as a key prevention target. SEB is a key target for the development of neutralizing antibodies against toxins to prevent and treat S. aureus infection. B. subtilis is used as a probiotic for human health. OBJECTIVE To investigate the efficacy of recombinant mSEB B. subtilis spores for reducing S. aureus intestinal colonization in mouse. METHODS Mice were orally immunized with recombinant mSEB spores three times a week for three weeks. After immunization, mice were challenged via oral gavage with 1 × 109 CFU of S. aureus (ATCC 14458). Fecal specific IgA and serum IgG1 and IgG2a were analyzed by ELISA. Peritoneal macrophages were isolated for qRT-PCR analysis of TNF-α, IL-6 and IL-1β mRNA expression. Colon contents samples underwent 16S rRNA sequencing for microbiota profiling. Intestinal RNA was extracted for transcriptome sequencing (RNA-seq), and differential pathways were analyzed using KEGG enrichment. Body weight and fecal viable S. aureus burden were monitored. RESULTS Oral mSEB spores correlated with elevated systemic and mucosal SEB-specific IgG1, IgG2a and fecal sIgA (P < 0.01). After S. aureus challenge, peritoneal macrophages from mSEB mice showed lower pro-inflammatory TNF-α, IL-6 and IL-1β transcripts, consistent with attenuated systemic inflammation. mSEB immunization also altered gut microbiota and increased the relative abundance of Barnesiella. Intestinal RNA-seq identified enriched antigen presentation and B cell receptor signaling gene sets in the mSEB group. On day 3 post-challenge, fecal S. aureus loads were 24.20 ± 3.967 × 104 CFU (Control), 8.081 ± 3.614 × 104 CFU (CotC) and 3.6 ± 1.030 × 104 CFU (mSEB), showing a pathogen-clearing phenotype linked to mSEB treatment. CONCLUSION Immunization with mSEB-displaying Bacillus subtilis spores correlates with SEB-specific mucosal and systemic antibody responses, blunted systemic inflammation, modified gut microbiota, and reduced intestinal S. aureus burdens post-challenge. The causal mechanisms underlying these changes remain to be clarified.

Characterization of a lytic Staphylococcus aureus phage JAsa55 and its biocontrol potential in milk.

Staphylococcus aureus (S. aureus) is a prominent foodborne pathogen that frequently causes food poisoning by contaminating various foods, particularly dairy products, and poses severe threats to food safety and public health. The increasing prevalence of multidrug-resistant S. aureus strains has further limited the efficacy of conventional interventions. In this study, we isolated and characterized a novel lytic phage JAsa55 using an MDR S. aureus strain as host. Transmission electron microscopy showed that JAsa55 possesses an icosahedral head and a long non-contractile tail, consistent with a siphovirus-like morphology. Notably, JAsa55 retained detectable activity after exposure to 4-60°C and remained active under pH 3.0-11.0. One-step growth analysis indicated a latent period (15 min) and an estimated burst size (∼500 PFU/cell) based on the first rise phase. Genome annotation did not identify obvious integrase genes, known virulence factors, or antimicrobial-resistance genes. In artificially contaminated milk, phage JAsa55 reduced S. aureus populations by up to ∼1.6 log CFU/mL at 4°C and ∼3.3 log CFU/mL at 25°C within 24 h. These findings suggest that JAsa55 has lytic activity against selected MDR S. aureus strains and may be further evaluated as a candidate component for phage-based control strategies in milk.