Human mucosal-associated invariant T cells respond to Mucorales species in a MR1-dependent manner.

Activation of mucosal-associated invariant T cells (MAIT cells) by certain bacteria, viruses, and yeast is well studied, but the activation potential of filamentous moulds from the order Mucorales is not known. Here, we show a rapid response of human MAIT cells against the Mucorales species Mucor circinelloides, Rhizopus arrhizus, and Rhizopus microsporus. This activation included upregulation of CD69 and degranulation marked by increased CD107a expression, while intracellular perforin and granzyme A expression were reduced. Furthermore, blocking of the antigen-presenting molecule major histocompatibility complex class I-related abrogated MAIT cell activation demonstrating a T cell receptor-dependent stimulation by Mucorales.

Transcriptional profile of the human skin pathogenic fungus Mucor irregularis in response to low oxygen.

Mucormycosis is one of the most invasive mycosis and has caused global concern in public health. Cutaneous mucormycosis caused by Mucor irregularis (formerly Rhizomucor variabilis) is an emerging disease in China. To survive in the human body, M. irregularis must overcome the hypoxic (low oxygen) host microenvironment. However, the exact molecular mechanism of its pathogenicity and adaptation to low oxygen stress environment is relatively unexplored. In this study, we used Illumina HiSeq technology (RNA-Seq) to determine and compare the transcriptome profile of M. irregularis CBS103.93 under normal growth condition and hypoxic stress. Our analyses demonstrated a series of genes involved in TCA, glyoxylate cycle, pentose phosphate pathway, and GABA shunt were down-regulated under hypoxic condition, while certain genes in the lipid/fatty acid metabolism and endocytosis were up-regulated, indicating that lipid metabolism was more active under hypoxia. Comparing the data with other important human pathogenic fungi such as Aspergillus spp., we found that the gene expression pattern and metabolism in responses to hypoxia in M. irregularis were unique and different. We proposed that these metabolic changes can represent a species-specific hypoxic adaptation in M. irregularis, and we hypothesized that M. irregularis could use the intra-lipid pool and lipid secreted in the infection region, as an extracellular nutrient source to support its hypoxic growth. Characterizing the significant differential gene expression in this species could be beneficial to uncover their role in hypoxia adaptation and fungalpathogenesis and further facilitate the development of novel targets in disease diagnosis and treatment against mucormycosis.

Higher In vitro Proliferation Rate of Rhizopus oryzae in Blood of Diabetic Individuals in Chronic Glycaemic Control Compared with Non-diabetic Individuals.

Metabolic control improves outcomes associated with mucormycosis. The aim of this study was to compare the in vitro proliferation of Rhizopus oryzae in blood of individuals with and without diabetes at different glycaemic levels. Ninety-five individuals were included. Blood samples from each participant were incubated with sporangiospores of R. oryzae. The germination, filamentation and growth of R. oryzae were compared at different time points. Four groups were defined, one without (group A, n = 30) and three with diabetes: group B (HbA1c ≤7%, N = 24), group C (HbA1c 7.1-9%, N = 20) and group D (HbA1c > 9%, N = 21). The percentage of germinated sporangiospores was higher in the group A after 6 h (group A 56% ± 3, group B 35% ± 4, group C 48% ± 4, group D 46% ± 1.4, p = 0.01), 12 h (group A 54% ± 1.4, group B 19% ± 4, group C 16% ± 1, group D 9.5% ± 5, p < 0.001) and 24 h (group A 29% ± 1, group B 12% ± 4, group C 13.5% ± 3.5, group D 12% ± 1, p < 0.01). The filamentation was higher in groups with diabetes. Group B showed higher filamentation grade than group A at 6 h (0.4 ± 0.04 vs 1 ± 0.09, p < 0.001) and 24 h (1.6 ± 0.05 vs 2.1 ± 0.1, p = 0.05). In conclusion, R. oryzae proliferation was higher among diabetic individuals, including good glycaemic control, than among non-diabetic individuals.

Calcineurin plays key roles in the dimorphic transition and virulence of the human pathogenic zygomycete Mucor circinelloides.

Many pathogenic fungi are dimorphic and switch between yeast and filamentous states. This switch alters host-microbe interactions and is critical for pathogenicity. However, in zygomycetes, whether dimorphism contributes to virulence is a central unanswered question. The pathogenic zygomycete Mucor circinelloides exhibits hyphal growth in aerobic conditions but switches to multi-budded yeast growth under anaerobic/high CO2 conditions. We found that in the presence of the calcineurin inhibitor FK506, Mucor exhibits exclusively multi-budded yeast growth. We also found that M. circinelloides encodes three calcineurin catalytic A subunits (CnaA, CnaB, and CnaC) and one calcineurin regulatory B subunit (CnbR). Mutations in the latch region of CnbR and in the FKBP12-FK506 binding domain of CnaA result in hyphal growth of Mucor in the presence of FK506. Disruption of the cnbR gene encoding the sole calcineurin B subunit necessary for calcineurin activity yielded mutants locked in permanent yeast phase growth. These findings reveal that the calcineurin pathway plays key roles in the dimorphic transition from yeast to hyphae. The cnbR yeast-locked mutants are less virulent than the wild-type strain in a heterologous host system, providing evidence that hyphae or the yeast-hyphal transition are linked to virulence. Protein kinase A activity (PKA) is elevated during yeast growth under anaerobic conditions, in the presence of FK506, or in the yeast-locked cnbR mutants, suggesting a novel connection between PKA and calcineurin. cnaA mutants lacking the CnaA catalytic subunit are hypersensitive to calcineurin inhibitors, display a hyphal polarity defect, and produce a mixture of yeast and hyphae in aerobic culture. The cnaA mutants also produce spores that are larger than wild-type, and spore size is correlated with virulence potential. Our results demonstrate that the calcineurin pathway orchestrates the yeast-hyphal and spore size dimorphic transitions that contribute to virulence of this common zygomycete fungal pathogen.

Multiple roles for hypoxia inducible factor 1-alpha in airway epithelial cells during mucormycosis.

During pulmonary mucormycosis, inhaled sporangiospores adhere to, germinate, and invade airway epithelial cells to establish infection. We provide evidence that HIF1α plays dual roles in airway epithelial cells during Mucorales infection. We observed an increase in HIF1α protein accumulation and increased expression of many known HIF1α-responsive genes during in vitro infection, indicating that HIF1α signaling is activated by Mucorales infection. Inhibition of HIF1α signaling led to a substantial decrease in the ability of R. delemar to invade cultured airway epithelial cells. Transcriptome analysis revealed that R. delemar infection induces the expression of many pro-inflammatory genes whose expression was significantly reduced by HIF1α inhibition. Importantly, pharmacological inhibition of HIF1α increased survival in a mouse model of pulmonary mucormycosis without reducing fungal burden. These results suggest that HIF1α plays two opposing roles during mucormycosis: one that facilitates the ability of Mucorales to invade the host cells and one that facilitates the ability of the host to mount an innate immune response.

Pathogenesis of mucormycosis.

Mucormycosis is a life-threatening infection that occurs in patients who are immunocompromised because of diabetic ketoacidosis, neutropenia, organ transplantation, and/or increased serum levels of available iron. Because of the increasing prevalence of diabetes mellitus, cancer, and organ transplantation, the number of patients at risk for this deadly infection is increasing. Despite aggressive therapy, which includes disfiguring surgical debridement and frequently adjunctive toxic antifungal therapy, the overall mortality rate is high. New strategies to prevent and treat mucormycosis are urgently needed. Understanding the pathogenesis of mucormycosis and the host response to invading hyphae ultimately will provide targets for novel therapeutic interventions. In this supplement, we review the current knowledge about the virulence traits used by the most common etiologic agent of mucormycosis, Rhizopus oryzae. Because patients with elevated serum levels of available iron are uniquely susceptible to mucormycosis and these infections are highly angioinvasive, emphasis is placed on the ability of the organism to acquire iron from the host and on its interactions with endothelial cells lining blood vessels. Several promising therapeutic strategies in preclinical stages are identified.

Lactoferrin, a potential iron-chelator as an adjunct treatment for mucormycosis - A comprehensive review.

Mucormycosis is a deadly infection which is caused by fungi of the order Mucorales including species belonging to the genus Rhizopus, Mucor, Mycocladus, Rhizomucor, Cunninghamella, and Apophysomyces. Despite antifungal therapy and surgical procedures, the mortality rate of this disease is about 90-100% which is exceptionally high. The hypersensitivity of patients with raised available serum iron indicates that the Mucorales are able to use host iron as a critical factor of virulence. This is because iron happens to be a crucial element playing its role in the growth of cells and development. In this review, we have described Lactoferrin (Lf) as a potential iron-chelator. Lf is a naturally occurring glycoprotein which is expressed in most of the biological fluids. Moreover, Lf possesses exclusive anti-inflammatory effects along with several anti-fungal effects that could prove to be helpful to the pathological physiology of inexorable mucormycosis cases. This literature summarises the biological insights into the Lf being considered as a potential fungistatic agent and an immune regulator. The review also proposes that unique potential of Lf as an iron-chelator can be exploited as the adjunct treatment for mucormycosis infection.

Leveraging Fungal and Human Calcineurin-Inhibitor Structures, Biophysical Data, and Dynamics To Design Selective and Nonimmunosuppressive FK506 Analogs.

Calcineurin is a critical enzyme in fungal pathogenesis and antifungal drug tolerance and, therefore, an attractive antifungal target. Current clinically accessible calcineurin inhibitors, such as FK506, are immunosuppressive to humans, so exploiting calcineurin inhibition as an antifungal strategy necessitates fungal specificity in order to avoid inhibiting the human pathway. Harnessing fungal calcineurin-inhibitor crystal structures, we recently developed a less immunosuppressive FK506 analog, APX879, with broad-spectrum antifungal activity and demonstrable efficacy in a murine model of invasive fungal infection. Our overarching goal is to better understand, at a molecular level, the interaction determinants of the human and fungal FK506-binding proteins (FKBP12) required for calcineurin inhibition in order to guide the design of fungus-selective, nonimmunosuppressive FK506 analogs. To this end, we characterized high-resolution structures of the Mucor circinelloides FKBP12 bound to FK506 and of the Aspergillus fumigatus, M. circinelloides, and human FKBP12 proteins bound to the FK506 analog APX879, which exhibits enhanced selectivity for fungal pathogens. Combining structural, genetic, and biophysical methodologies with molecular dynamics simulations, we identify critical variations in these structurally similar FKBP12-ligand complexes. The work presented here, aimed at the rational design of more effective calcineurin inhibitors, indeed suggests that modifications to the APX879 scaffold centered around the C15, C16, C18, C36, and C37 positions provide the potential to significantly enhance fungal selectivity. IMPORTANCE Invasive fungal infections are a leading cause of death in the immunocompromised patient population. The rise in drug resistance to current antifungals highlights the urgent need to develop more efficacious and highly selective agents. Numerous investigations of major fungal pathogens have confirmed the critical role of the calcineurin pathway for fungal virulence, making it an attractive target for antifungal development. Although FK506 inhibits calcineurin, it is immunosuppressive in humans and cannot be used as an antifungal. By combining structural, genetic, biophysical, and in silico methodologies, we pinpoint regions of the FK506 scaffold and a less immunosuppressive analog, APX879, centered around the C15 to C18 and C36 to C37 positions that could be altered with selective extensions and/or deletions to enhance fungal selectivity. This work represents a significant advancement toward realizing calcineurin as a viable target for antifungal drug discovery.

Pharmacokinetics of liposomal amphotericin B in pleural fluid.

We report the penetration of liposomal amphotericin B into the pleural fluid of a patient with pulmonary zygomycosis and empyema. The ratio of area under the concentration-versus-time curve in pleural fluid (AUC(pleural fluid)) to that in serum (AUC(serum)) for liposomal amphotericin B over 24 h was 9.4%, with pleural fluid concentrations of 2.12 to 4.91 microg/ml. Given the relatively low level of intrapleural penetration of liposomal amphotericin B, chest tube drainage may be warranted for successful treatment of zygomycotic empyema.

The iron chelator deferasirox protects mice from mucormycosis through iron starvation.

Mucormycosis causes mortality in at least 50% of cases despite current first-line therapies. Clinical and animal data indicate that the presence of elevated available serum iron predisposes the host to mucormycosis. Here we demonstrate that deferasirox, an iron chelator recently approved for use in humans by the US FDA, is a highly effective treatment for mucormycosis. Deferasirox effectively chelated iron from Rhizopus oryzae and demonstrated cidal activity in vitro against 28 of 29 clinical isolates of Mucorales at concentrations well below clinically achievable serum levels. When administered to diabetic ketoacidotic or neutropenic mice with mucormycosis, deferasirox significantly improved survival and decreased tissue fungal burden, with an efficacy similar to that of liposomal amphotericin B. Deferasirox treatment also enhanced the host inflammatory response to mucormycosis. Most importantly, deferasirox synergistically improved survival and reduced tissue fungal burden when combined with liposomal amphotericin B. These data support clinical investigation of adjunctive deferasirox therapy to improve the poor outcomes of mucormycosis with current therapy. As iron availability is integral to the pathogenesis of other infections (e.g., tuberculosis, malaria), broader investigation of deferasirox as an antiinfective treatment is warranted.

Iron Assimilation during Emerging Infections Caused by Opportunistic Fungi with emphasis on Mucorales and the Development of Antifungal Resistance.

Iron is a key transition metal required by most microorganisms and is prominently utilised in the transfer of electrons during metabolic reactions. The acquisition of iron is essential and becomes a crucial pathogenic event for opportunistic fungi. Iron is not readily available in the natural environment as it exists in its insoluble ferric form, i.e., in oxides and hydroxides. During infection, the host iron is bound to proteins such as transferrin, ferritin, and haemoglobin. As such, access to iron is one of the major hurdles that fungal pathogens must overcome in an immunocompromised host. Thus, these opportunistic fungi utilise three major iron acquisition systems to overcome this limiting factor for growth and proliferation. To date, numerous iron acquisition pathways have been fully characterised, with key components of these systems having major roles in virulence. Most recently, proteins involved in these pathways have been linked to the development of antifungal resistance. Here, we provide a detailed review of our current knowledge of iron acquisition in opportunistic fungi, and the role iron may have on the development of resistance to antifungals with emphasis on species of the fungal basal lineage order Mucorales, the causative agents of mucormycosis.

Diagnostic value of a semi-nested PCR for the diagnosis of mucormycosis and aspergillosis from paraffin-embedded tissue: A single center experience.

OBJECTIVE: The main aim of our study was to investigate the diagnostic value of a molecular method for the diagnosis of mucormycosis and aspergillosis from formalin-fixed and paraffin-embedded (FFPE) tissues. METHODS: A retrospective chart review identified all cases with histology reports mentioning the presence of fungi with morphological characteristics of either Aspergillus or mucormycetes, for the period 2005-2012. Paraffin blocks were retrieved from the archives of the Department of Pathology. A semi-nested PCR specific for the detection of mucormycetes and Aspergillus species was applied in FFPE tissue from the above blocks. Results were compared with those of histological (gold standard) and microbiological methods. RESULTS: Twenty cases with fungal hyphae in tissue were revealed. Mucormycetes were detected in 9 cases (45%) by PCR, in only 4 of which culture was available. Species of Aspergillus were detected in 8 cases (40%) by PCR, two of which were co-infection with mucormycetes. Five patients had other fungi, non-detectable with this specific PCR. At least one sample per patient was positive by PCR. Seven out of 30 samples tested overall were false negative. The calculated sensitivity of this method in our setting was 79.3% (95% CI: 60.3-91.9%); specificity was 100%. CONCLUSIONS: The specific PCR used appears to be an easy and useful tool for the prompt and accurate diagnosis of mucormycosis and aspergillosis, in combination with histology and direct examination. Mucormycosis was more frequent than aspergillosis during the study period, highlighting the importance of continuous epidemiological surveillance of these serious infections.

Endogenous Heparinoids May Cause Bleeding in Mucor Infection and can be Detected by Nonactivated Thromboelastometry and Treated by Recombinant Activated Factor VII: A Case Report.

Mucormycosis is an aggressive fungal infection, which invades endothelial cells of blood vessels. This condition might lead to destruction of endothelium and release of heparin-like substances to the bloodstream and cause life-threatening bleeding, which is not well described in the literature.We present a patient with mucormycosis who experienced life-threatening bleeding, although no standard laboratory test could detect any coagulopathy.The cause of bleeding-coagulopathy was detected only by nonactivated thromboelastometry (NATEM), which revealed the presence of heparin-like substances. After treatment with recombinant activated FVII rotational thromboelastometry, results improved and the patient stopped bleeding. Regular application of the drug was necessary during acute phase of infection to prevent further bleeding.In this case report, we show that NATEM can detect the presence of heparin-like substances in bleeding patient with mucormycosis infection and that recombinant activated FVII can be used to stop and prevent bleeding until infection resolves.

Bicarbonate correction of ketoacidosis alters host-pathogen interactions and alleviates mucormycosis.

Patients with diabetic ketoacidosis (DKA) are uniquely predisposed to mucormycosis, an angioinvasive fungal infection with high mortality. Previously, we demonstrated that Rhizopus invades the endothelium via binding of fungal CotH proteins to the host receptor GRP78. Here, we report that surface expression of GRP78 is increased in endothelial cells exposed to physiological concentrations of ß-hydroxy butyrate (BHB), glucose, and iron that are similar to those found in DKA patients. Additionally, expression of R. oryzae CotH was increased within hours of incubation with DKA-associated concentrations of BHB, glucose, and iron, augmenting the ability of R. oryzae to invade and subsequently damage endothelial cells in vitro. BHB exposure also increased fungal growth and attenuated R. oryzae neutrophil-mediated damage. Further, mice given BHB developed clinical acidosis and became extremely susceptible to mucormycosis, but not aspergillosis, while sodium bicarbonate reversed this susceptibility. BHB-related acidosis exerted a direct effect on both GRP78 and CotH expression, an effect not seen with lactic acidosis. However, BHB also indirectly compromised the ability of transferrin to chelate iron, as iron chelation combined with sodium bicarbonate completely protected endothelial cells from Rhizopus-mediated invasion and damage. Our results dissect the pathogenesis of mucormycosis during ketoacidosis and reinforce the importance of careful metabolic control of the acidosis to prevent and manage this infection.

A zebrafish larval model reveals early tissue-specific innate immune responses to Mucor circinelloides.

Mucormycosis is an emerging fungal infection that is clinically difficult to manage, with increasing incidence and extremely high mortality rates. Individuals with diabetes, suppressed immunity or traumatic injury are at increased risk of developing disease. These individuals often present with defects in phagocytic effector cell function. Research using mammalian models and phagocytic effector cell lines has attempted to decipher the importance of the innate immune system in host defence against mucormycosis. However, these model systems have not been satisfactory for direct analysis of the interaction between innate immune effector cells and infectious sporangiospores in vivo. Here, we report the first real-time in vivo analysis of the early innate immune response to mucormycete infection using a whole-animal zebrafish larval model system. We identified differential host susceptibility, dependent on the site of infection (hindbrain ventricle and swim bladder), as well as differential functions of the two major phagocyte effector cell types in response to viable and non-viable spores. Larval susceptibility to mucormycete spore infection was increased upon immunosuppressant treatment. We showed for the first time that macrophages and neutrophils were readily recruited in vivo to the site of infection in an intact host and that spore phagocytosis can be observed in real-time in vivo. While exploring innate immune effector recruitment dynamics, we discovered the formation of phagocyte clusters in response to fungal spores that potentially play a role in fungal spore dissemination. Spores failed to activate pro-inflammatory gene expression by 6 h post-infection in both infection models. After 24 h, induction of a pro-inflammatory response was observed only in hindbrain ventricle infections. Only a weak pro-inflammatory response was initiated after spore injection into the swim bladder during the same time frame. In the future, the zebrafish larva as a live whole-animal model system will contribute greatly to the study of molecular mechanisms involved in the interaction of the host innate immune system with fungal spores during mucormycosis.

Peroxynitrite formation in the orbit of diabetics with rhinocerebral mucormycosis.

OBJECTIVE: To evaluate whether an intact respiratory burst exists within the orbit of diabetics with rhinocerebral mucormycosis. METHODS: Immunohistochemical detection of nitrotyrosine in the orbital tissue of diabetics requiring exenteration due to rhinocerebral mucormycosis. Nitrotyrosine is the stable product of the nitration of tyrosine residues by peroxynitrite. Peroxynitrite is a potent oxidant produced by the combination of superoxide and nitric oxide during the respiratory burst. RESULTS: Four specimens were analyzed. All showed focal areas of specific staining against nitrotyrosine of the walls and internal structures of fungal organisms. CONCLUSIONS: An intact respiratory burst is present in the orbit of diabetics during infection with rhinocerebral mucormycosis. Possible mechanisms of peroxynitrite's microbicidal effects and reasons for a deficiency in diabetics are discussed.

Gross, histological and immunohistochemical features of mucormycosis in the platypus.

Nine male and five female adult free-living platypuses, obtained in a prospective capture-release study from northern Tasmania, exhibited gross features of cutaneous mycosis caused by Mucor amphibiorum. The lesions were present on the hind limbs (six cases), front limbs (four), tail (five), dorsal trunk (three) and ventral trunk (one). They varied in size, and ranged from raised red nodules or plaques, which sometimes exuded purulent material, to ulcerated lesions with central cavitation, red exuding centres and raised epidermal margins. Older lesions were covered either partly or fully by thickened and irregular epidermis. Histological examination of skin biopsies revealed discrete, poorly encapsulated granulomas, or more commonly a diffuse granulomatous or pyogranulomatous inflammation. Inflammatory cells consisted of neutrophils or eosinophils, sparse plasma cells and lymphocytes, many macrophages and occasional multinucleated giant cells. Fibrovascular tissue was diffusely and irregularly scattered in the granulomatous regions. Sphaerules characteristic of M. amphibiorum infection were observed in all lesions. The cutaneous distribution of the lesions and the natural history of the platypus indicated that entry of M. amphibiorum may have been via superficial skin wounds. T cells were the predominant infiltrating lymphoid cells in the diffuse lesions, indicating the importance of the cell-mediated response to infection.