Biology subjects

Walch, M.

Publications and source records attributed to Walch, M..

6 recordsLinked to original sources

bioRxiv2026

Granulysin-Based pH-Sensitive Antimicrobial Nanocarriers for Treatment of Multidrug-Resistant Bacterial Wound Infections

Multidrug resistant (MDR) bacterial wound infections are an increasing clinical challenge and require alternatives to conventional antibiotics. Although antimicrobial proteins offer promise, their therapeutic use is limited by poor stability, proteolytic degradation, reduced activity under physiological conditions, and potential toxicity. This work reports pH-sensitive lipid nanocarriers composed of granulysin (GNLY) and oleic acid (OA) for antimicrobial delivery to infected tissues. At neutral pH, GNLY is retained within OA-based nanocarriers and protected from proteolytic degradation. At pH 5.0, such as in infected wounds, the carriers undergo structural reorganization and release GNLY, restoring antimicrobial activity. OAGNLY (32 {micro}g/mL) achieved >3-log reductions in Staphylococcus aureus and Escherichia coli within 1 hour, and up to 4-log reductions in Pseudomonas aeruginosa and Acinetobacter baumannii, at physiological salt concentrations where free GNLY was largely inactive. Minimum inhibitory concentrations were 16 {micro}g/mL for MRSA and 32 {micro}g/mL for colistin-resistant E. coli. Ultrastructural analysis using transmission electron microscopy revealed disruptions of bacterial membranes and intracellular structures following OAGNLY treatment. In a murine surgical wound infection model, topical application of OAGNLY for 4 hours reduced bacterial burden by >5 logs and significantly decreased inflammation, as confirmed by histological analysis. In parallel, OAGNLY demonstrated minimal cytotoxicity to mammalian cells at active concentrations. These findings identify OAGNLY nanocarriers as a promising platform for pH-responsive delivery of GNLY and highlight their potential application for treating MDR skin and soft tissue infections..

microbiology↗

bioRxiv2025

Detection and isolation of H5N1 clade 2.3.4.4b high pathogenicity avian influenza virus from ticks (Ornithodoros maritimus) recovered from a naturally infected slender-billed gull (Chroicocephalus genei)

Laridae birds, such as gulls, are known reservoirs of H13 and H16 low pathogenicity avian influenza virus (LPAIV) subtypes. However, during the recent outbreaks linked to the reemergence of high pathogenicity avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b of the Goose/Guangdong lineage, European populations of Laridae birds suffered significant losses. HPAI cases were reported not only along the coastlines but also inland areas, particularly in France and Central Europe. During a diagnostic investigation of a group of Laridae birds, part of a HPAIV outbreak reported in the South of France in 2023, larval stages of Ornithodoros maritimus, a nidicolous soft tick parasitizing seabirds, were recovered from a slender-billed gull (Chroicocephalus genei). Affected birds exhibited gross and histopathological lesions consistent with systemic HPAIV infection. Immunohistochemistry revealed marked neurotropism, oculotropism and multicentric epitheliotropism. Viral isolation and sequencing analysis confirmed the presence of HPAIV H5N1 clade 2.3.4.4b in both the gull and ectoparasites, showing from 99.64% to 100% nucleotide identity across five of eight RNA segments. While additional research is needed to properly assess the vector competence of O. maritimus for HPAIV, ticks may represent an interesting non-invasive surveillance tool for these viruses. This is the first time a HPAIV has been successfully isolated from tick larvae. These findings represent a first step toward understanding the potential role played by ticks in the spread of avian influenza viruses within marine bird colonies and among other ecosystems, considering the occurrence of specific behavioral traits, such as kleptoparasitim and the position of gulls at the interface between wild and domestic species.

microbiology↗

bioRxiv2025

Duck Slurry as a Matrix for Avian Influenza Virus Surveillance and Genetic Characterization in Domestic Flocks

Avian influenza viruses (AIVs) circulate widely in domestic and wild birds and continue to pose major risks to animal and public health, in particular those of high pathogenicity (HP). Ducks play a key role in AIV ecology due to frequent subclinical infections and high viral shedding. Efficient environmental surveillance approaches are needed to complement costly individual testing, especially in the context of large-scale anti-H5 vaccination as implemented in France. We evaluated duck slurry, the wastewater produced in duck fattening units, as a matrix for AIV detection and optimized molecular protocols for sensitive molecular detection and genetic characterization. Slurry samples (n = 172) were collected from 37 duck farms in southwestern France between May 2024 and March 2025. Among several extraction strategies, RNA extraction from the solid fraction using TRIzol LS followed by magnetic bead purification yielded the highest sensitivity. Using this optimized protocol, 82% of samples tested positive for AIV RNA, with 30% of positives being H5-positive; no H7 viruses were detected. Whole-segment RT-PCR and sequencing were successful for shorter genomic segments, enabling subtype determination, although virus isolation consistently failed. These findings demonstrate that slurry is a promising matrix for AIV detection, providing valuable molecular data. Slurry-based surveillance may therefore serve as an effective complement to individual testing and improve early warning capacities for influenza surveillance in a One Health perspective. ImportanceIn France, current surveillance of high pathogenicity avian influenza in ducks relies mainly on individual swabs, which may miss subclinical or transient infections, particularly with low-pathogenicity strains. By targeting slurry, a wastewater generated in duck fattening units, we developed an affordable and practical approach for environmental surveillance. Slurry samples captured high levels of avian influenza RNA and allowed partial genomic characterization despite failed virus isolation. This strategy is directly relevant to monitoring avian influenza viruses dynamics under current anti-H5 vaccination and can be extended to other livestock systems. Duck slurry-based surveillance thus represents an efficient One Health tool to strengthen preparedness against avian influenza outbreaks.

microbiology↗

bioRxiv2025

Plasmodium falciparum subverts neutrophil function via host miR-451a loaded extracellular vesicles driving bacterial superinfection susceptibility

Malaria caused by Plasmodium falciparum (Pf) compromise innate immunity, yet the underlying mechanisms remain elusive. The immune dysregulation caused by the parasite may lead to bacterial superinfections and increase mortality. We reveal that Pf exploits extracellular vesicles (EVs) secreted by infected red blood cells (iRBC-EVs) to deliver host-derived miR451a to human neutrophils, impairing their antimicrobial defences. Neutrophil phagocytosis of iRBC-EVs suppresses reactive oxygen species (ROS) production and compromised microbicidal activity against Salmonella typhimurium. Microfluidic assays show that miR451a transfer significantly disrupts neutrophil chemotaxis and swarming upon microbial challenge. Transcriptomic profiling indicates that EVs and miR451a reprogram neutrophil gene expression, notably upregulating ferroptosis-related genes, suggesting a role in further impairing immune responses. We have uncovered a novel mechanism of iRBC-EVs-induced neutrophil immune suppression and provide insights into increased susceptibility to bacterial superinfections in malaria. These findings have implications for therapeutic strategies aimed at mitigating bacterial superinfections and sepsis in malaria-endemic regions.

immunology↗

bioRxiv2024

Granulysin antimicrobial activity promotes dormancy in Mycobacterium tuberculosis

Human tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) remains a global public health threat. Granulomas constitute a hallmark of TB pathogenesis that can clear, contain or exacerbate an infection. Containment is exploited by Mtb as a hideout to persist in a dormant, antibiotic-tolerant state only to resuscitate upon immunosuppression. The immune determinants of a granulomatous response driving Mtb persistence remain elusive. We here combined an ex vivo granuloma model with peripheral blood mononuclear cell (PBMC) specimens from TB patients and a high-dimensional mass cytometry (CyTOF) approach to shed light on the immune factors prompting Mtb dormancy. Compared to healthy controls, patient-derived ex vivo granulomas rapidly force Mtb to adopt a dormant-like state; an observation that correlates with the presence of activated innate (-like) cytotoxic lymphocytes. We further demonstrate that Mtb dormancy is induced by direct exposure to granulysin, thereby unravelling an immune escape mechanism to cytotoxic lymphocyte activity.

immunology↗

bioRxiv2021

Genome mosaicism in field strains of Mycoplasma bovis as footprints of in-host horizontal chromosomal transfer

Horizontal gene transfer was long thought to be marginal in Mollicutes, but the capacity of some of these wall-less bacteria to exchange large chromosomal regions has been recently documented. Mycoplasma chromosomal transfer (MCT) is an unconventional mechanism that relies on the presence of a functional integrative conjugative element (ICE) in at least one partner and involves the horizontal acquisition of small and large chromosomal fragments from any part of the donor genome, which results in progenies composed of an infinitive variety of mosaic genomes. The present study focuses on Mycoplasma bovis, an important pathogen of cattle responsible for major economic losses worldwide. By combining phylogenetic tree reconstructions and detailed comparative genome analyses of 36 isolates collected in Spain (2016-2018) we confirmed the mosaic nature of 16 field isolates and mapped chromosomal transfers exchanged between their hypothetical ancestors. This study provides evidence that MCT can take place in the field, most likely during co-infections by multiple strains. Because mobile genetic elements (MGEs) are classical contributors of genome plasticity, the presence of phages, insertion sequences (ISs) and ICEs was also investigated. Data revealed that these elements are widespread within the M. bovis species and evidenced classical horizontal transfer of phages and ICEs in addition to MCT. These events contribute to wide-genome diversity and reorganization within this species and may have a tremendous impact on diagnostic and disease control. IMPORTANCEMycoplasma bovis is a major pathogen of cattle with significant detrimental economic and animal welfare on cattle rearing worldwide. Understanding the evolution and the adaptative potential of pathogenic mycoplasma species in the natural host is essential to combating them. In this study, we documented the occurrence of mycoplasma chromosomal transfer, an atypical mechanism of horizontal gene transfer, in field isolates of M. bovis that provide new insights into the evolution of this pathogenic species in their natural host. Despite these events are expected to occur at low frequency, their impact is accountable for genome-wide variety and reorganization within M. bovis species, which may compromise both diagnostic and disease control.

evolutionary biology↗