Antifungal activities of tacrolimus in combination with antifungal agents against fluconazole-susceptible and fluconazole-resistant Trichosporon asahii isolates

Development of a yeast cell based method for efficient screening of high yield tacrolimus production strain

Tacrolimus (FK506) is a widely used and clinically important immunosuppressant drug that can be produced by fermentation of Streptomyces tsukubaensis. The industrial strains are typically obtained through multiple rounds of mutagenesis and screening, a labor-intensive process. We have established an efficient yeast cell based screening method for the evolutionary process of high-FK506-yielding strain. The S. tsukubaensis strains of different FK506 yields were tested for zone of growth inhibition of the wild type and calcineurin mutant (cnb1∆) yeast strains. We found that different FK506 yields correspond well to altered yeast growth inhibitions. Based on the combinational inhibition effects of FK506 with different antifungals that have been frequently reported, we also tested the zone of inhibition by addition of fluconazole, amphotericin B and caspofungin to the medium. In the end, for the best screening performance, we systemically evaluated the strategy when different yeast strains and different antifungals were used according to the clarity, size, and divergence of the inhibition circles. Using different yeast strains and antifungals, we successfully broadened the screening spectrum. An efficient high-FK506-yield S. tsukubaensis screening method has been established and optimized.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03870-y.

Antifungal Activity and Potential Action Mechanism of Allicin against Trichosporon asahii

Trichosporon asahii is an emerging opportunistic pathogen that causes potentially fatal disseminated trichosporonosis. The global prevalence of coronavirus disease 2019 (COVID-19) poses an increasing fungal infection burden caused by T. asahii. Allicin is the main biologically active component with broad-spectrum antimicrobial activity in garlic. In this study, we performed an in-depth analysis of the antifungal characteristics of allicin against T. asahii based on physiological, cytological, and transcriptomic assessments. In vitro, allicin inhibited the growth of T. asahii planktonic cells and biofilm cells significantly. In vivo, allicin improved the mean survival time of mice with systemic trichosporonosis and reduced tissue fungal burden. Electron microscopy observations clearly demonstrated damage to T. asahii cell morphology and ultrastructure caused by allicin. Furthermore, allicin increased intracellular reactive oxygen species (ROS) accumulation, leading to oxidative stress damage in T. asahii cells. Transcriptome analysis showed that allicin treatment disturbed the biosynthesis of cell membrane and cell wall, glucose catabolism, and oxidative stress. The overexpression of multiple antioxidant enzymes and transporters may also place an additional burden on cells, causing them to collapse. Our findings shed new light on the potential of allicin as an alternative treatment strategy for trichosporonosis. IMPORTANCE Systemic infection caused by T. asahii has recently been recognized as an important cause of mortality in hospitalized COVID-19 patients. Invasive trichosporonosis remains a significant challenge for clinicians, due to the limited therapeutic options. The present work suggests that allicin holds great potential as a therapeutic candidate for T. asahii infection. Allicin demonstrated potent in vitro antifungal activity and potential in vivo protective effects. In addition, transcriptome sequencing provided valuable insights into the antifungal effects of allicin.

Novel avenues for identification of new antifungal drugs and current challenges

INTRODUCTION

: Some of otherwise useful fungi are pathogenic to humans, and unfortunately, the number of these pathogens is increasing. In addition to common skin infections, these opportunistic pathogens are able to cause severe, often incurable, systemic mycoses.

AREAS COVERED

: The number of antifungal drugs is limited, especially drugs that can be used for systemic administration, and resistance to these drugs is very common. This review summarizes various approaches to the discovery and development of new antifungal drugs, provides an overview of the most important molecules in terms of basic (laboratory) research and compounds currently in clinical trials, and focuses on drug repurposing strategy, while providing an overview of drugs of other indications that have been tested in vitro for their antifungal activity for possible expansion of antifungal drugs and/or support of existing antimycotics.

EXPERT OPINION

: Despite the limitations of the research of new antifungal drugs by pharmaceutical manufacturers, in addition to innovated molecules based on clinically used drugs, several completely new small entities with unique mechanisms of actions have been identified. The identification of new molecular targets that offer alternatives for the development of new unique selective antifungal highly effective agents has been an important outcome of repurposing of non-antifungal drugs to antifungal drug. Also, given the advances in monoclonal antibodies and their application to immunosuppressed patients, it may seem possible to predict a more optimistic future for antifungal therapy than has been the case in recent decades.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.

Inhibition of Candida albicans in vivo and in vitro by antimicrobial peptides chromogranin A-N12 through microRNA-155/suppressor of cytokine signaling 1 axis

Antimicrobial peptides (AMPs) have proven to inhibit a variety of pathogens. Chromogranin A-N12 (CGA-N12) is a kind of AMP, and it is characterized by stable structure, high anti-Candida activity, and good safety. However, it remains unclear whether CGA-N12 could effectively inhibit the growth of Candida albicans (C. albicans). Colony forming assays were used to measure minimal inhibitory concentration (MIC), minimal fungicidal concentration (MFC), and time-kill curve. Disseminated C. albicans rabbit model was established to investigate the influence of CGA-N12 on histological damage. The protein and mRNA levels of suppressor of cytokine signaling 1 (SOCS1) after treatment were investigated. The MIC and MFC of CGA-N12 against C. albicans was 6 mg/mL. CGA-N12 considerably inhibited germ tube formation of C. albicans. The fungal load in the tissues and inflammatory factors in the serum were suppressed by CGA-N12. CGA-N12 significantly reduced the histological changes caused by C. albicans, and the protein and mRNA levels of SOCS1 were markedly inhibited. The inhibition effect of CGA-N12 on C. albicans and significant improvement of histological damage by CGA-N12 through microRNA-155/SOCS1 axis were proved in this study. This study proposes a novel therapeutic strategy for the treatment and prevention of C. albicans.

Abbreviations: AMPs: Antimicrobial peptides; MIC: Minimal inhibitory concentration; MFC: Minimal fungicidal concentration; AIDS: Acquired immune deficiency syndrome; PBS: Phosphate buffer saline; FBS: Fetal bovine serum; ROS: Reactive oxygen species; CFU: Colony formation unit; CGA: Chromogranin A; SOCS1: Suppressor of cytokine signaling 1; SDA: Sabouraud Dextrose Agar; GRAVY: Grand average of hydropathicity; C. parapsilosis: Candida parapsilosis; C. albicans: Candida albicans

Insight into the antifungals used to address human infection due to Trichosporon spp.: a scoping review

Trichosporonosis infections have been increasing worldwide. Providing adequate treatment for these infections remains a challenge. This scoping review contains information about potential antifungals to treat this pathology. Using online databases, we found 76 articles published between 2010 and 2020 related to this topic. Classic antifungals, molecules and biomolecules, repositioned drugs and natural products have been tested against species of Trichosporon. Experimental research has lacked depth or was limited to in vitro and in vivo tests, so there are no promising new candidates for the clinical treatment of patients with trichosporonosis. Furthermore, most studies did not present appropriate scientific criteria for drug tests, compromising their quality.

Drug repurposing strategies in the development of potential antifungal agents

Abstract

The morbidity and mortality caused by invasive fungal infections are increasing across the globe due to developments in transplant surgery, the use of immunosuppressive agents, and the emergence of drug-resistant fungal strains, which has led to a challenge in terms of treatment due to the limitations of three classes of drugs. Hence, it is imperative to establish effective strategies to identify and design new antifungal drugs. Drug repurposing is a potential way of expanding the application of existing drugs. Recently, various existing drugs have been shown to be useful in the prevention and treatment of invasive fungi. In this review, we summarize the currently used antifungal agents. In addition, the most up-to-date information on the effectiveness of existing drugs with antifungal activity is discussed. Moreover, the antifungal mechanisms of existing drugs are highlighted. These data will provide valuable knowledge to stimulate further investigation and clinical application in this field.

Key points

• Conventional antifungal agents have limitations due to the occurrence of drug-resistant strains.

• Non-antifungal drugs act as antifungal agents in various ways toward different targets.

• Non-antifungal drugs with antifungal activity are demonstrated as effective antifungal strategies.

Effects of calcineurin inhibitors, cyclosporine A and tacrolimus (FK506), on the activity of antifungal drugs against Candida spp

Introduction. The simultaneous use of antifungals with immunosuppressive agents has become a necessity for patients taking immunosuppressive therapy. However, antifungal drugs are problematic because of their limited target.Hypothesis. Scientists have been searching for new antifungals and some compounds with at least additive effects on antifungals. Calcineurin inhibitors used as immunosuppressive agents also attract attention due to their antifungal property.Aim. To evaluate the activity of two calcineurin inhibitors alone and in combination with amphotericin B (AMB), caspofungin (CAS), itraconazole (ITR), voriconazole (VOR) and fluconazole (FLU).Methodology. MICs of AMB, CAS, ITR, VOR, FLU and cyclosporine A (CsA) and tacrolimus (TAC) as calcineurin inhibitors were evaluated by the broth microdilution method against Candida albicans (n=13), C. krusei (n=7) and C. glabrata (n=10). Checkerboard and time-kill methods were performed to investigate the activity of combining calcineurin inhibitors with antifungal drugs.Results. The lowest MIC values were detected with VOR for all Candida isolates tested. Although we did not detect any inhibition for CsA or TAC alone at concentrations tested in this study, the combinations of CAS with CsA showed the highest synergistic activity (36.7%) by the checkerboard method, and CAS with CsA and ITR with TAC combinations exhibited apparent synergistic interaction by the time-kill method. However, the combinations of both CsA and TAC with AMB resulted in antagonistic interactions, especially against C. krusei isolate in time-kill testing.Conclusion. Synergistic interactions in the combinations of TAC or CsA with antifungal drugs, except for AMB, in many concentrations was found to be promising in terms of the treatment of patients with fungal infections.

Immunosuppression in the Management of Presumed Non-infective Uveitis; Are We Sure What We are Treating? Notes on the Antimicrobial Properties of the Systemic Immunosuppressants

PURPOSE

To describe the antimicrobial effects of immunosuppressants used for presumed autoimmune uveitis, and to discuss the potential importance of these effects in the context of increasing knowledge of the human microbiomes and their influence on inflammation.

METHODS

Literature review.

REVIEW OF EVIDENCE

All immunosuppressants have intrinsic antimicrobial effects; these vary considerably between drugs, and include antibacterial, antiviral and antifungal action. Immunosuppression is known to affect the composition of the gut microbiome, and alterations in microbiome composition are known to affect inflammations including uveitis.

CONCLUSIONS

Oral immunosuppressants are assumed to act on presumed autoimmune uveitis by downregulation of, or other interference with, an aberrant immune response. However, their antimicrobial properties are usually forgotten, and in the context of increasing knowledge of the involvement of microbes in the initiation of, and also potentially the perpetuation of, tissue inflammation, these effects may prove to be a fundamental part of their action.

Exploring the resistance mechanisms in Trichosporon asahii: Triazoles as the last defense for invasive trichosporonosis

Trichosporon asahii has recently been recognized as an emergent fungal pathogen able to cause invasive infections in neutropenic cancer patients as well as in critically ill patients submitted to invasive medical procedures and broad-spectrum antibiotic therapy. T. asahii is the main pathogen associated with invasive trichosporonosis worldwide. Treatment of patients with invasive trichosporonosis remains a controversial issue, but triazoles are mentioned by most authors as the best first-line antifungal therapy. There is mounting evidence supporting the claim that fluconazole (FLC) resistance in T. asahii is emerging worldwide. Since 2000, 15 publications involving large collections of T. asahii isolates described non-wild type isolates for FLC and/or voriconazole. However, very few papers have addressed the epidemiology and molecular mechanism of antifungal resistance in Trichosporon spp. Data available suggest that continuous exposure to azoles can induce mutations in the ERG11 gene, resulting in resistance to this class of antifungal drugs. A recent report characterizing T. asahii azole-resistant strains found several genes differentially expressed and highly mutated, including genes related to the Target of Rapamycin (TOR) pathway, indicating that evolutionary modifications on this pathway induced by FLC stress may be involved in developing azole resistance. Finally, we provided new data suggesting that hyperactive efflux pumps may play a role as drug transporters in FLC resistant T. asahii strains.

Epidemiology of antifungal susceptibility: Review of literature

Fungal infections are a major cause of morbidity and mortality despite the latest developments of diagnostic tools and therapeutic options. Early initiation of the appropriate antifungal therapy has been demonstrated to have a direct impact on the patient's outcome. Antifungal susceptibility testing methods are available to detect antifungal resistance and to determine the best treatment for a specific fungus. American and European standards have been developed, as well as equivalent commercial systems, which are more appropriate for clinical laboratories. These studies have allowed the development of interpretative breakpoints against the most frequent agents of fungal infections in the world. Surveillance of antifungal susceptibility patterns can provide the local drug resistance data to the clinicians, which can further aid better management of patients. Antifungal susceptibility tests have become essential tools to identify resistance to antifungals, to know the local and global disease epidemiology and to guide the treatment of fungal diseases. The distribution of species and the prevalence of antifungal resistance in fungi isolates varied among different areas. Here we summarize the epidemiology of antifungal susceptibility pattern of different fungal species.

MTL genotypes, phenotypic switching, and susceptibility profiles of Candida parapsilosis species group compared to Lodderomyces elongisporus

Reference isolates of Candida parapsilosis (n = 8), Candida metapsilosis (n = 6), Candida orthopsilosis (n = 7), and Lodderomyces elongisporus (n = 11) were analyzed to gain insight into their pathobiology and virulence mechanisms. Initial evaluation using BBL Chromagar Candida medium misidentified L. elongisporus isolates as C. albicans. Polymerase chain reaction analysis of isolate MTL idiomorphs revealed that all C. parapsilosis isolates were MTLa homozygous and no MTL α1, α2, a1, or a2 gene was detected in L. elongisporus isolates. For C. orthopsilosis, two isolates were MTLa homozygous and five were MTL-heterozygous. Similarly, one C. metapsilosis isolate was MTLα homozygous whereas five were MTL-heterozygous. Isolate phenotypic switching analysis revealed potential phenotypic switching in the MTLα homozygous C. metapsilosis isolate, resulting in concomitant elongated cell formation. Minimum inhibitory concentrations of fluconazole (FLC) and FK506, alone or in combination, were determined by checkerboard assay, with data analyzed using the fractional inhibitory concentration index model. Synergistic or additive effects of these compounds were commonly observed in C. parapsilosis and L. elongisporus isolates. No killer activity was observed in the studied isolates, as determined phenotypically. No significant difference in virulence was seen for the four species in a Galleria mellonella model (P > 0.05). In conclusion, our results demonstrated phenotypic switching of C. metapsilosis CBS 2315 and that FLC and FK506 represent a promising drug combination against C. parapsilosis and L. elongisporus. The findings of the present study contribute to our understanding of the biology, diagnosis, and new possible treatments of the C. parapsilosis species group and L. elongisporus.