Non-albicans Candida Species: Immune Response, Evasion Mechanisms, and New Plant-Derived Alternative Therapies

First report of Candida auris in Guangdong, China: clinical and microbiological characteristics of 7 episodes of candidemia

Candida auris is an emerging multidrug-resistant fungal pathogen worldwide. To date, it has not been reported in Guangdong, China. For the first time, we reported 7 cases of C. auris candidemia from two hospitals in Guangdong. The clinical and microbiological characteristics of these cases were investigated carefully. Two geographic clades, i.e. III and I, were found popular in different hospitals by whole genome sequencing analyses. All C. auris isolates from bloodstream were resistant to fluconazole, 5 of which belonged to Clade III harbouring VF125AL mutation in the ERG11 gene. The isolates with Clade I presented Y132F mutation in the ERG11 gene as well as resistance to amphotericin B. All isolates exhibited strong biofilm-forming capacity and non-aggregative phenotype. The mean time from admission to onset of C. auris candidemia was 39.4 days (range: 12 - 80 days). Despite performing appropriate therapeutic regimen, 42.9% (3/7) of patients experienced occurrences of C. auris candidemia and colonization after the first positive bloodstream. C. auris colonization was still observed after the first C. auris candidemia for 81 days in some patient. Microbiologic eradication from bloodstream was achieved in 85.7% (6/7) of patients at discharge. In conclusion, this study offers a crucial insight into unravelling the multiple origins of C. auris in Guangdong, highlighting great challenges in clinical prevention and control.

Mangiferin potentiates the activity of antifungal agents against fluconazole-resistant Candida spp

Aim: To evaluate the antifungal activity of mangiferin against Candida spp. resistant to fluconazole.Materials & methods: The antifungal activity of mangiferin was assessed using broth microdilution and its interaction with azoles and amphotericin B was evaluated by checkerboard. The activity of mangiferin against Candida spp. biofilms was assessed using the MTT colorimetric assay and its possible mechanism of action was evaluated using flow cytometry.Results: Mangiferin showed activity against Candida albicans, Candida tropicalis and Candida parapsilosis resistant to fluconazole and showed synergism with azoles and amphotericin B. Mangiferin increased the activity of antifungals against Candida biofilms and caused depolarization of the mitochondrial membrane and externalization of phosphatidylserine, suggesting apoptosis.Conclusion: mangiferin combined with antifungals has potential against Candida spp.

Candida tropicalis PMT2 Is a Dispensable Gene for Viability but Required for Proper Interaction with the Host

Candidemia is an opportunistic mycosis with high morbidity and mortality rates. Even though Candida albicans is the main causative agent, other Candida species, such as Candida tropicalis, are relevant etiological agents of candidiasis and candidemia. Compared with C. albicans, there is currently limited information about C. tropicalis' biological aspects, including those related to the cell wall and the interaction with the host. Currently, it is known that its cell wall contains O-linked mannans, and the contribution of these structures to cell fitness has previously been addressed using cells subjected to chemical treatments or in mutants where O-linked mannans and other wall components are affected. Here, we generated a C. tropicalis pmt2∆ null mutant, which was affected in the first step of the O-linked mannosylation pathway. The null mutant was viable, contrasting with C. albicans where this gene is essential. The phenotypical characterization showed that O-linked mannans were required for filamentation; proper cell wall integrity and organization; biofilm formation; protein secretion; and adhesion to extracellular matrix components, in particular to fibronectin; and type I and type II collagen. When interacting with human innate immune cells, it was found that this cell wall structure is dispensable for cytokine production, but mutant cells were more phagocytosed by monocyte-derived macrophages. Furthermore, the null mutant cells showed virulence attenuation in Galleria mellonella larvae. Thus, O-linked mannans are minor components of the cell wall that are involved in different aspects of C. tropicalis' biology.

Candida parapsilosis: Heterogeneous and strain-specific expression of secreted aspartic proteases (Sapp1 and Sapp2)

The increasing prevalence of Candida parapsilosis as a causative agent of fungal infections underscores the need to comprehensively understand its virulence factors. Secreted aspartic proteases (Saps) play a significant role in adhesion events, promoting biofilm formation, causing tissue damage and evading the host's immune response. In C. parapsilosis, three Saps have been identified: Sapp1, Sapp2 and Sapp3. The present study investigates the production dynamics of Sapp1 and Sapp2 across 10 clinical isolates of C. parapsilosis using various approaches. Each fungal isolate demonstrated the capability to utilize bovine serum albumin (BSA) as the sole nitrogen source, as evidenced by its degradation in a cell-free culture medium, forming low molecular mass polypeptides. Interestingly, the degradation of different proteinaceous substrates, such as BSA, human serum albumin (HSA), gelatin and hemoglobin, was typically isolate-dependent. Notably, higher proteolysis of HSA compared to BSA, gelatin and hemoglobin was observed. A quantitative assay revealed that the cleavage of a peptide fluorogenic substrate (cathepsin D) was isolate-specific, ranging from 44.15 to 270.61 fluorescence arbitrary units (FAU), with a mean proteolysis of 150.7 FAU. The presence of both Sapp1 and Sapp2 antigens on the cell surface of these fungal isolates was confirmed through immunological detection employing specific anti-Sapp1 and anti-Sapp2 antibodies. The surface levels of Sapp1 were consistently higher, up to fourfold, compared to Sapp2. Similarly, higher levels of Sapp1 than Sapp2 were detected in fungal secretions. This study provides insights into the dynamic expression and regulation of Sapps in C. parapsilosis, highlighting a known virulence factor that is considered a potential target for drug development against this increasingly prominent pathogen.

Oral Candida in post-radiotherapy patients with xerostomia/hyposalivation: A narrative review

OBJECTIVE

Head and Neck Cancer (HNC) patients receiving radiotherapy (RT) often suffer from xerostomia and/or hyposalivation. As saliva plays an important antimicrobial and cleansing roles, these patients are at higher risks of opportunistic infections. This narrative review aims to provide an overview of current evidence on oral Candida colonisation and infection in these patients.

METHODS

A literature review of clinical studies on oral Candida colonisation and candidiasis in HNC patients receiving radiotherapy/chemoradiotherapy was conducted.

RESULTS

Many clinical studies found high levels of Candida colonisation and a substantial proportion of post-RT HNC patients suffering from oropharyngeal candidiasis (OPC). Importantly, oral Candida could be a reservoir for life-threatening systemic infection in immunocompromised patients. The rising prevalence of non-albicans Candida species and drug-resistant infections has made identification of Candida species and antifungal susceptibility more important. Recent advances in oral microbiome and its interactions with Candida are discussed. This review also offers perspectives on limitations of current evidence and suggestions for future research.

CONCLUSION

Further research to better understand Candida carriage, microbiome, OPC, and xerostomia/hyposalivation post-RT would aid in devising a more comprehensive long-term management plan and novel therapeutic approaches for HNC patients to achieve the full benefits of RT while minimising side effects.

Extracellular vesicle production: A bidirectional effect in the interplay between host and Candida fungi

Candida fungi exploit various virulence strategies to invade the human host, while host cells employ diverse mechanisms to maintain homeostasis and respond to infection. Extracellular vesicles (EVs) are integral components of the multifaceted landscape of host-pathogen interactions, with their abundant production by all contributors involved in these complex and dynamic relations. Herein, we present the current state of knowledge regarding the host response by releasing EVs in reaction to Candida, as well as the influence of fungal EVs on the functionality of the confronted host cells. Fungal vesicles contribute to enhanced adhesion of pathogens to human cells as evidenced for C. auris, and may modulate the production of several cytokines, including IL-6, IL-8, IL-10, IL-12p40, TGF-β and TNF-α, thereby exerting pro-infective and pro-inflammatory effects, as described for C. albicans and other Candida species. Whereas the biosynthesis of EVs by host cells can dynamically modulate the proliferation and viability of fungal cells and affect the candidacidal functionality of other effector cells. The reciprocal influence of EVs from host cells and Candida pathogens is a key focus, explaining their significant role in cell signaling and interkingdom communication.

Candida albicans skin infection in diabetic patients: An updated review of pathogenesis and management

Candida species, commensal residents of human skin, are recognized as the cause of cutaneous candidiasis across various body surfaces. Individuals with weakened immune systems, particularly those with immunosuppressive conditions, are significantly more susceptible to this infection. Diabetes mellitus, a major metabolic disorder, has emerged as a critical factor inducing immunosuppression, thereby facilitating Candida colonization and subsequent skin infections. This comprehensive review examines the prevalence of different types of Candida albicans-induced cutaneous candidiasis in diabetic patients. It explores the underlying mechanisms of pathogenicity and offers insights into recommended preventive measures and treatment strategies. Diabetes notably increases vulnerability to oral and oesophageal candidiasis. Additionally, it can precipitate vulvovaginal candidiasis in females, Candida balanitis in males, and diaper candidiasis in young children with diabetes. Diabetic individuals may also experience candidal infections on their nails, hands and feet. Notably, diabetes appears to be a risk factor for intertrigo syndrome in obese individuals and periodontal disorders in denture wearers. In conclusion, the intricate relationship between diabetes and cutaneous candidiasis necessitates a comprehensive understanding to strategize effective management planning. Further investigation and interdisciplinary collaborative efforts are crucial to address this multifaceted challenge and uncover novel approaches for the treatment, management and prevention of both health conditions, including the development of safer and more effective antifungal agents.

Stephanoascus ciferrii Complex: The Current State of Infections and Drug Resistance in Humans

In recent years, the incidence of fungal infections in humans has increased dramatically, accompanied by an expansion in the number of species implicated as etiological agents, especially environmental fungi never involved before in human infection. Among fungal pathogens, Candida species are the most common opportunistic fungi that can cause local and systemic infections, especially in immunocompromised individuals. Candida albicans (C. albicans) is the most common causative agent of mucosal and healthcare-associated systemic infections. However, during recent decades, there has been a worrying increase in the number of emerging multi-drug-resistant non-albicans Candida (NAC) species, i.e., C. glabrata, C. parapsilosis, C. tropicalis, C. krusei, C. auris, and C. ciferrii. In particular, Candida ciferrii, also known as Stephanoascus ciferrii or Trichomonascus ciferrii, is a heterothallic ascomycete yeast-like fungus that has received attention in recent decades as a cause of local and systemic fungal diseases. Today, the new definition of the S. ciferrii complex, which consists of S. ciferrii, Candida allociferrii, and Candida mucifera, was proposed after sequencing the 18S rRNA gene. Currently, the S. ciferrii complex is mostly associated with non-severe ear and eye infections, although a few cases of severe candidemia have been reported in immunocompromised individuals. Low susceptibility to currently available antifungal drugs is a rising concern, especially in NAC species. In this regard, a high rate of resistance to azoles and more recently also to echinocandins has emerged in the S. ciferrii complex. This review focuses on epidemiological, biological, and clinical aspects of the S. ciferrii complex, including its pathogenicity and drug resistance.

Exploring Non-Thermal Plasma and UV Radiation as Biofilm Control Strategies against Foodborne Filamentous Fungal Contaminants

In recent years, non-thermal plasma (NTP) has emerged as a promising tool for decontamination and disinfection within the food industry. Given the increasing resistance of microbial biofilms to conventional disinfectants and their adverse environmental effects, this method has significant potential for eliminating biofilm formation or mitigating the metabolic activity of grown biofilms. A comparative study was conducted evaluating the efficacy of UV radiation and NTP in eradicating mature biofilms of four common foodborne filamentous fungal contaminants: Alternaria alternata, Aspergillus niger, Fusarium culmorum, and Fusarium graminearum. The findings reveal that while UV radiation exhibits variable efficacy depending on the duration of exposure and fungal species, NTP induces substantial morphological alterations in biofilms, disrupting hyphae, and reducing extracellular polymeric substance production, particularly in A. alternata and F. culmorum. Notably, scanning electron microscopy analysis demonstrates significant disruption of the hyphae in NTP-treated biofilms, indicating its ability to penetrate the biofilm matrix, which is a promising outcome for biofilm eradication strategies. The use of NTP could offer a more environmentally friendly and potentially more effective alternative to traditional disinfection methods.

Transcriptional Reprogramming of Candida tropicalis in Response to Isoespintanol Treatment

Candida tropicalis, an opportunistic pathogen, ranks among the primary culprits of invasive candidiasis, a condition notorious for its resistance to conventional antifungal drugs. The urgency to combat these drug-resistant infections has spurred the quest for novel therapeutic compounds, with a particular focus on those of natural origin. In this study, we set out to evaluate the impact of isoespintanol (ISO), a monoterpene derived from Oxandra xylopioides, on the transcriptome of C. tropicalis. Leveraging transcriptomics, our research aimed to unravel the intricate transcriptional changes induced by ISO within this pathogen. Our differential gene expression analysis unveiled 186 differentially expressed genes (DEGs) in response to ISO, with a striking 85% of these genes experiencing upregulation. These findings shed light on the multifaceted nature of ISO's influence on C. tropicalis, spanning a spectrum of physiological, structural, and metabolic adaptations. The upregulated DEGs predominantly pertained to crucial processes, including ergosterol biosynthesis, protein folding, response to DNA damage, cell wall integrity, mitochondrial activity modulation, and cellular responses to organic compounds. Simultaneously, 27 genes were observed to be repressed, affecting functions such as cytoplasmic translation, DNA damage checkpoints, membrane proteins, and metabolic pathways like trans-methylation, trans-sulfuration, and trans-propylamine. These results underscore the complexity of ISO's antifungal mechanism, suggesting that it targets multiple vital pathways within C. tropicalis. Such complexity potentially reduces the likelihood of the pathogen developing rapid resistance to ISO, making it an attractive candidate for further exploration as a therapeutic agent. In conclusion, our study provides a comprehensive overview of the transcriptional responses of C. tropicalis to ISO exposure. The identified molecular targets and pathways offer promising avenues for future research and the development of innovative antifungal therapies to combat infections caused by this pathogenic yeast.

Contribution of N-Linked Mannosylation Pathway to Candida parapsilosis and Candida tropicalis Biofilm Formation

Background

Mycoses are a growing threat to human health, and systemic candidiasis caused by Candida parapsilosis and Candida tropicalis is frequent in immunocompromised patients. Biofilm formation is a virulence factor found in these organisms, as sessile cells adhere to surfaces, the stratification and production of extracellular matrix provides protection and resistance to antifungal drugs. Previous evidence indicated that the N-linked mannosylation pathway is relevant to C. albicans biofilms, but its contribution to other species remains unknown.

Methods

C. parapsilosis and C. tropicalis och1∆ mutants, which have a disrupted N-linked mannosylation pathway, were used to form biofilms. In addition, wild-type and mutant cells were also treated to remove N-linked mannans or block this pathway. Biofilms were analyzed by quantifying the included fungal biomass, and extracellular matrix components. Moreover, gene expression and secreted hydrolytic enzymes were also quantified in these biofilms.

Results

The och1∆ mutants showed a reduced ability to form biofilms in both fungal species when compared to the wild-type and control strains. This observation was confirmed by trimming N-linked mannans from walls or blocking the pathway with tunicamycin B. According to this observation, mutant, and treated cells showed an altered composition of the extracellular matrix and increased susceptibility to antifungal drugs when compared to control or untreated cells. The gene expression of secreted virulence factors, such as aspartyl proteinases and phospholipases, was normal in all the tested cells but the secreted activity was reduced, suggesting a defect in the secretory pathway, which was later confirmed by treating cells with brefeldin A.

Conclusion

Proper N-linked mannosylation is required for biofilm formation in both C. parapsilosis and C. tropicalis. Disruption of this posttranslational modification affected the secretory pathway, offering a link between glycosylation and biofilm formation.

Molecular Cloning, Heterologous Expression, Purification, and Evaluation of Protein-Ligand Interactions of CYP51 of Candida krusei Azole-Resistant Fungal Strain

Due to the increasing prevalence of fungal diseases caused by fungi of the genus Candida and the development of pathogen resistance to available drugs, the need to find new effective antifungal agents has increased. Azole antifungals, which are inhibitors of sterol-14α-demethylase or CYP51, have been widely used in the treatment of fungal infections over the past two decades. Of special interest is the study of C. krusei CYP51, since this fungus exhibit resistance not only to azoles, but also to other antifungal drugs and there is no available information about the ligand-binding properties of CYP51 of this pathogen. We expressed recombinant C. krusei CYP51 in E. coli cells and obtained a highly purified protein. Application of the method of spectrophotometric titration allowed us to study the interaction of C. krusei CYP51 with various ligands. In the present work, the interaction of C. krusei CYP51 with azole inhibitors, and natural and synthesized steroid derivatives was evaluated. The obtained data indicate that the resistance of C. krusei to azoles is not due to the structural features of CYP51 of this microorganism, but rather to another mechanism. Promising ligands that demonstrated sufficiently strong binding in the micromolar range to C. krusei CYP51 were identified, including compounds 99 (Kd = 1.02 ± 0.14 µM) and Ch-4 (Kd = 6.95 ± 0.80 µM). The revealed structural features of the interaction of ligands with the active site of C. krusei CYP51 can be taken into account in the further development of new selective modulators of the activity of this enzyme.

The Yeast and Hypha Phases of Candida krusei Induce the Apoptosis of Bovine Mammary Epithelial Cells via Distinct Signaling Pathways

Infection with Candida spp. is a significant cause of bovine mastitis globally. We previously found that C. krusei was the main pathogen causing mycotic mastitis in dairy cows in Yinchuan, Ningxia, China. However, whether the infection of this pathogen could induce apoptosis in BMECs remained unclear. In this report, we explored the apoptosis and underlying mechanism of BMECs induced by C. krusei yeast and hypha phases using a pathogen/host cell co-culture model. Our results revealed that both the yeast and hypha phases of C. krusei could induce BMEC apoptosis; however, the yeast phase induced more cell apoptosis than the hypha phase, as assessed via electronic microscopy and flow cytometry assays. This finding was further corroborated via the measurement of the mitochondrial membrane potential (MMP) and the TUNEL test. Infection by both the yeast and hypha phases of C. krusei greatly induced the expression of proteins associated with cell death pathways and important components of toll-like receptor (TLR) signaling, including TLR2 and TLR4 receptors, as determined via a Western blotting assay. BMECs mainly underwent apoptosis after infection by the C. krusei yeast phase through a mitochondrial pathway. Meanwhile, BMEC apoptosis induced by the C. krusei hypha phase was regulated by a death ligand/receptor pathway. In addition, C. krusei-induced BMEC apoptosis was regulated by both the TLR2/ERK and JNK/ERK signaling pathways. These data suggest that the yeast phase and hypha phase of C. krusei induce BMEC apoptosis through distinct cell signaling pathways. This study represents a unique perspective on the molecular processes underlying BMEC apoptosis in response to C. krusei infection.

Pseudolaric Acid A: A Promising Antifungal Agent Against Prevalent Non-albicans Candida Species

Purpose

The non-albicans Candida (NAC) species have recently gained great importance worldwide due to the increasing proportion in candida causing bloodstream infections. This investigation aimed to explore the efficacy of Pseudolaric acid A (PAA, a diterpenoid derived from Pseudolarix kaempferi) and its synergistic effect with fluconazole (FLC) against NAC species, including C. tropicalis, C. parapsilosis complex, and C. glabrata.

Methods

The microdilution checkerboard assay and time-killing curves were performed to detect the antifungal efficiency. To examine the integrity of cell walls and membranes, calcofluor white stain and propidium iodide stain were used. The changes of intracellular ultrastructure in Candida cells after treatment were observed using transmission electron microscopy. Changes in cell viability with the autophagy inhibitor 3-MA were assessed by the XTT method.

Results

It was revealed that PAA alone is effective on C. tropicalis, C. parapsilosis sensu stricto, C. orthopsilosis, and C. metapsilosis (MIC 8-128 µg/mL). Strong synergism against FLC-resistant C. tropicalis was observed (FICI 0.07-0.281), when PAA and FLC were combined. PAA had dose-dependently detrimental effects on C. tropicalis cell membranes. Moreover, increased vacuoles and autophagosome formation were found in C. tropicalis exposed to PAA. And the inhibitory effect of PAA against C. tropicalis can be relieved by autophagy inhibitor 3-MA in a certain concentration range. Ultrastructural alterations of C. tropicalis were more pronounced under the combination of PAA and FLC, including separation of the cell membrane from the cell wall, increased number of vacuoles, and degradation of organelles.

Conclusion

These observations indicated that PAA and its combination with FLC could be a promising therapeutic candidate for treating infections caused by NAC species.