Peptidorhamanomannan: A surface fungal glycoconjugate from Scedosporium aurantiacum and Scedosporium minutisporum and its recognition by macrophages

Glycoconjugates: Advances in modern medicines and human health

Glycans and their glycoconjugates are complex biomolecules that are crucial for various biological processes. Glycoconjugates are found in all domains of life. They are covalently linked to key biomolecules such as proteins and lipids to play a pivotal role in cell signaling, adhesion, and recognition. The diversity of glycan structures and the associated complexity of glycoconjugates is the reason for their role in intricate biosynthetic pathways. Glycoconjugates play an important role in various diseases where they are actively involved in the immune response as well as in the pathogenicity of infectious diseases. In addition, various autoimmune diseases have been linked to glycosylation defects of different biomolecules, making them an important molecule in the field of medicine. The glycoconjugates have been explored for the development of therapeutics and vaccines, representing a breakthrough in medical science. They also hold significance in research studies to understand the mechanisms behind various biological processes. Finally, glycoconjugates have found an emerging role in various industrial and environmental applications which have been discussed here.

Scedosporiosis and lomentosporiosis: modern perspectives on these difficult-to-treat rare mold infections

SUMMARYAlthough Scedosporium species and Lomentospora prolificans are uncommon causes of invasive fungal diseases (IFDs), these infections are associated with high mortality and are costly to treat with a limited armamentarium of antifungal drugs. In light of recent advances, including in the area of new antifungals, the present review provides a timely and updated overview of these IFDs, with a focus on the taxonomy, clinical epidemiology, pathogenesis and host immune response, disease manifestations, diagnosis, antifungal susceptibility, and treatment. An expansion of hosts at risk for these difficult-to-treat infections has emerged over the last two decades given the increased use of, and broader population treated with, immunomodulatory and targeted molecular agents as well as wider adoption of antifungal prophylaxis. Clinical presentations differ not only between genera but also across the different Scedosporium species. L. prolificans is intrinsically resistant to most currently available antifungal agents, and the prognosis of immunocompromised patients with lomentosporiosis is poor. Development of, and improved access to, diagnostic modalities for early detection of these rare mold infections is paramount for timely targeted antifungal therapy and surgery if indicated. New antifungal agents (e.g., olorofim, fosmanogepix) with novel mechanisms of action and less cross-resistance to existing classes, availability of formulations for oral administration, and fewer drug-drug interactions are now in late-stage clinical trials, and soon, could extend options to treat scedosporiosis/lomentosporiosis. Much work remains to increase our understanding of these infections, especially in the pediatric setting. Knowledge gaps for future research are highlighted in the review.

Functional insights into human macrophage response against Scedosporium apiospermum and Scedosporium dehoogii

Fungal infections caused by Scedosporium species are rising among immunocompromised and immunocompetent patients. Within the immunocompetent group, patients with cystic fibrosis (pwCF) are at high risk of developing a chronic airway colonization by these molds. While S. apiospermum is one of the major species encountered in the lungs of pwCF, S. dehoogii has rarely been reported. The innate immune response is believed to be critical for host defense against fungal infections. However, its role has only recently been elucidated and the immune mechanisms against Scedosporium species are currently unknown. In this context, we undertook a comparative investigation of macrophage-mediated immune responses toward S. apiospermum and S. dehoogii conidia. Our data showed that S. apiospermum and S. dehoogii conidia strongly stimulated the expression of a set of pro-inflammatory cytokines and chemokines such as IL-1β, IL-8, IL-6 and TNFα. We demonstrated that S. dehoogii was more potent in stimulating the early release of pro-inflammatory cytokines and chemokines while S. apiospermum induced a late inflammatory response at a higher level. Flow cytometry analysis showed that M1-like macrophages were able to internalize both S. apiospermum and S. dehoogii conidia, with a similar intracellular killing rate for both species. In conclusion, these results suggest that M1-like macrophages can rapidly initiate a strong immune response against both S. apiospermum and S. dehoogii. This response is characterized by a similar killing of internalized conidia, but a different time course of cytokine production.

Deciphering the Role of PIG1 and DHN-Melanin in Scedosporium apiospermum Conidia

Scedosporium apiospermum is a saprophytic filamentous fungus involved in human infections, of which the virulence factors that contribute to pathogenesis are still poorly characterized. In particular, little is known about the specific role of dihydroxynaphtalene (DHN)-melanin, located on the external layer of the conidia cell wall. We previously identified a transcription factor, PIG1, which may be involved in DHN-melanin biosynthesis. To elucidate the role of PIG1 and DHN-melanin in S. apiospermum, a CRISPR-Cas9-mediated PIG1 deletion was carried out from two parental strains to evaluate its impact on melanin biosynthesis, conidia cell-wall assembly, and resistance to stress, including the ability to survive macrophage engulfment. ΔPIG1 mutants did not produce melanin and showed a disorganized and thinner cell wall, resulting in a lower survival rate when exposed to oxidizing conditions, or high temperature. The absence of melanin increased the exposure of antigenic patterns on the conidia surface. PIG1 regulates the melanization of S. apiospermum conidia, and is involved in the survival to environmental injuries and to the host immune response, that might participate in virulence. Moreover, a transcriptomic analysis was performed to explain the observed aberrant septate conidia morphology and found differentially expressed genes, underlining the pleiotropic function of PIG1.

Extracellularly Released Molecules by the Multidrug-Resistant Fungal Pathogens Belonging to the Scedosporium Genus: An Overview Focused on Their Ecological Significance and Pathogenic Relevance

The multidrug-resistant species belonging to the Scedosporium genus are well recognized as saprophytic filamentous fungi found mainly in human impacted areas and that emerged as human pathogens in both immunocompetent and immunocompromised individuals. It is well recognized that some fungi are ubiquitous organisms that produce an enormous amount of extracellular molecules, including enzymes and secondary metabolites, as part of their basic physiology in order to satisfy their several biological processes. In this context, the molecules secreted by Scedosporium species are key weapons for successful colonization, nutrition and maintenance in both host and environmental sites. These biologically active released molecules have central relevance on fungal survival when colonizing ecological places contaminated with hydrocarbons, as well as during human infection, particularly contributing to the invasion/evasion of host cells and tissues, besides escaping from the cellular and humoral host immune responses. Based on these relevant premises, the present review compiled the published data reporting the main secreted molecules by Scedosporium species, which operate important physiopathological events associated with pathogenesis, diagnosis, antimicrobial activity and bioremediation of polluted environments.

The Host Immune Response to Scedosporium/Lomentospora

Infections caused by the opportunistic pathogens Scedosporium/Lomentospora are on the rise. This causes problems in the clinic due to the difficulty in diagnosing and treating them. This review collates information published on immune response against these fungi, since an understanding of the mechanisms involved is of great interest in developing more effective strategies against them. Scedosporium/Lomentospora cell wall components, including peptidorhamnomannans (PRMs), α-glucans and glucosylceramides, are important immune response activators following their recognition by TLR2, TLR4 and Dectin-1 and through receptors that are yet unknown. After recognition, cytokine synthesis and antifungal activity of different phagocytes and epithelial cells is species-specific, highlighting the poor response by microglial cells against L. prolificans. Moreover, a great number of Scedosporium/Lomentospora antigens have been identified, most notably catalase, PRM and Hsp70 for their potential medical applicability. Against host immune response, these fungi contain evasion mechanisms, inducing host non-protective response, masking fungal molecular patterns, destructing host defense proteins and decreasing oxidative killing. In conclusion, although many advances have been made, many aspects remain to be elucidated and more research is necessary to shed light on the immune response to Scedosporium/Lomentospora.

Peptidorhamnomannans From Scedosporium and Lomentospora Species Display Microbicidal Activity Against Bacteria Commonly Present in Cystic Fibrosis Patients

Scedosporium and Lomentospora species are filamentous fungi that cause a wide range of infections in humans. They are usually found in the lungs of cystic fibrosis (CF) patients and are the second most frequent fungal genus after Aspergillus species. Several studies have been recently performed in order to understand how fungi and bacteria interact in CF lungs, since both can be isolated simultaneously from patients. In this context, many bacterial molecules were shown to inhibit fungal growth, but little is known about how fungi could interfere in bacterial development in CF lungs. Scedosporium and Lomentospora species present peptidorhamnomannans (PRMs) in their cell wall that play crucial roles in fungal adhesion and interaction with host epithelial cells and the immune system. The present study aimed to analyze whether PRMs extracted from Lomentospora prolificans, Scedosporium apiospermum, Scedosporium boydii, and Scedosporium aurantiacum block bacterial growth and biofilm formation in vitro. PRM from L. prolificans and S. boydii displayed the best bactericidal effect against methicillin resistant Staphylococcus aureus (MRSA), Burkholderia cepacia, and Escherichia coli, but not Pseudomonas aeruginosa, all of which are the most frequently found bacteria in CF lungs. In addition, biofilm formation was inhibited in all bacteria tested using PRMs at minimal inhibitory concentration (MIC). These results suggest that PRMs from the Scedosporium and Lomentospora surface seem to play an important role in Scedosporium colonization in CF patients, helping to clarify how these pathogens interact to each other in CF lungs.