Candida infections, causes, targets, and resistance mechanisms: traditional and alternative antifungal agents

Evolutionary Emergence of Drug Resistance in Candida Opportunistic Pathogens

Fungal infections, such as candidiasis caused by Candida, pose a problem of growing medical concern. In developed countries, the incidence of Candida infections is increasing due to the higher survival of susceptible populations, such as immunocompromised patients or the elderly. Existing treatment options are limited to few antifungal drug families with efficacies that vary depending on the infecting species. In this context, the emergence and spread of resistant Candida isolates are being increasingly reported. Understanding how resistance can evolve within naturally susceptible species is key to developing novel, more effective treatment strategies. However, in contrast to the situation of antibiotic resistance in bacteria, few studies have focused on the evolutionary mechanisms leading to drug resistance in fungal species. In this review, we will survey and discuss current knowledge on the genetic bases of resistance to antifungal drugs in Candida opportunistic pathogens. We will do so from an evolutionary genomics perspective, focusing on the possible evolutionary paths that may lead to the emergence and selection of the resistant phenotype. Finally, we will discuss the potential of future studies enabled by current developments in sequencing technologies, in vitro evolution approaches, and the analysis of serial clinical isolates.

Phagocytes from Mice Lacking the Sts Phosphatases Have an Enhanced Antifungal Response to Candida albicans

Mice lacking expression of the homologous phosphatases Sts-1 and Sts-2 (Sts^−/− mice) are resistant to disseminated candidiasis caused by the fungal pathogen Candida albicans. To better understand the immunological mechanisms underlying the enhanced resistance of Sts^−/− mice, we examined the kinetics of fungal clearance at early time points. In contrast to the rapid C. albicans growth seen in normal kidneys during the first 24 h postinfection, we observed a reduction in kidney fungal CFU within Sts^−/− mice beginning at 12 to 18 h postinfection. This corresponds to the time period when large numbers of innate leukocytes enter the renal environment to counter the infection. Because phagocytes of the innate immune system are important for host protection against pathogenic fungi, we evaluated responses of bone marrow leukocytes. Relative to wild-type cells, Sts^−/− marrow monocytes and bone marrow-derived dendritic cells (BMDCs) displayed a heightened ability to inhibit C. albicans growth ex vivo. This correlated with significantly enhanced production of reactive oxygen species (ROS) by Sts^−/− BMDCs downstream of Dectin-1, a C-type lectin receptor that plays a critical role in stimulating host responses to fungi. We observed no visible differences in the responses of other antifungal effector pathways, including cytokine production and inflammasome activation, despite enhanced activation of the Syk tyrosine kinase downstream of Dectin-1 in Sts^−/− cells. Our results highlight a novel mechanism regulating the immune response to fungal infections. Further understanding of this regulatory pathway could aid the development of therapeutic approaches to enhance protection against invasive candidiasis.

Systemic candidiasis caused by fungal Candida species is becoming an increasingly serious medical problem for which current treatment is inadequate. Recently, the Sts phosphatases were established as key regulators of the host antifungal immune response. In particular, genetic inactivation of Sts significantly enhanced survival of mice infected intravenously with Candida albicans. The Sts^−/−in vivo resistance phenotype is associated with reduced fungal burden and an absence of inflammatory lesions. To understand the underlying mechanisms, we studied phagocyte responses. Here, we demonstrate that Sts^−/− phagocytes have heightened responsiveness to C. albicans challenge relative to wild-type cells. Our data indicate the Sts proteins negatively regulate phagocyte activation via regulating selective elements of the Dectin-1–Syk tyrosine kinase signaling axis. These results suggest that phagocytes lacking Sts respond to fungal challenge more effectively and that this enhanced responsiveness partially underlies the profound resistance of Sts^−/− mice to systemic fungal challenge.

Candida Infections and Therapeutic Strategies: Mechanisms of Action for Traditional and Alternative Agents

The Candida genus comprises opportunistic fungi that can become pathogenic when the immune system of the host fails. Candida albicans is the most important and prevalent species. Polyenes, fluoropyrimidines, echinocandins, and azoles are used as commercial antifungal agents to treat candidiasis. However, the presence of intrinsic and developed resistance against azole antifungals has been extensively documented among several Candida species. The advent of original and re-emergence of classical fungal diseases have occurred as a consequence of the development of the antifungal resistance phenomenon. In this way, the development of new satisfactory therapy for fungal diseases persists as a major challenge of present-day medicine. The design of original drugs from traditional medicines provides new promises in the modern clinic. The urgent need includes the development of alternative drugs that are more efficient and tolerant than those traditional already in use. The identification of new substances with potential antifungal effect at low concentrations or in combination is also a possibility. The present review briefly examines the infections caused by Candida species and focuses on the mechanisms of action associated with the traditional agents used to treat those infections, as well as the current understanding of the molecular basis of resistance development in these fungal species. In addition, this review describes some of the promising alternative molecules and/or substances that could be used as anticandidal agents, their mechanisms of action, and their use in combination with traditional drugs.

Lack of Impact by SCY-078, a First-in-Class Oral Fungicidal Glucan Synthase Inhibitor, on the Pharmacokinetics of Rosiglitazone, a Substrate for CYP450 2C8, Supports the Low Risk for Clinically Relevant Metabolic Drug-Drug Interactions

SCY‐078, the first in a new class of β 1,3‐glucan synthesis inhibitors, is being developed as an oral and intravenous antifungal treatment for Candida and Aspergillus species fungal infections. In vitro, studies indicated SCY‐078 is an inhibitor of cytochrome P450 (CYP) 2C8 with markedly lower effect over other CYP isozymes. To examine clinically relevant effects of the potential interaction with SCY‐078, this phase 1, open‐label, 2‐period crossover study evaluated the pharmacokinetic parameters of rosiglitazone, a sensitive substrate of CYP2C8 metabolism, in the absence and presence of SCY‐078 dosed to therapeutically relevant SCY‐078 concentration exposure after repeat dosing. Healthy adult subjects were randomized to 2 treatment sequences: a single oral 4‐mg rosiglitazone dose alone on day 1 or a 1250‐mg SCY‐078 loading dose on day 1 followed by a once‐daily 750‐mg SCY‐078 dose for an additional 7 days (reflecting the clinical regimen evaluated during phase 2 studies for infections by Candida species) and concurrent administration of a single oral 4‐mg rosiglitazone dose on day 3, before alternating following a ≥10‐day washout. The exposure to SCY‐078 observed in this study was in line with the intended exposure for treatment of invasive fungal infections. The 90% confidence intervals for rosiglitazone exposure geometric mean ratios were within the prespecified no effect interval of 0.70‐1.43. Additionally, maximum concentration values for rosiglitazone and its metabolite, N‑desmethylrosiglitazone, were not significantly affected by co‐administration with SCY‐078. Overall, rosiglitazone exposure was not impacted to a clinically meaningful extent with co‐administration of therapeutically relevant SCY‐078 concentration exposure after repeat dosing. The results are indicative of low risk for interaction of SCY‐078 with drugs metabolized via the CYP family of enzymes.

Opciones terapéuticas frente a especies de Candida resistentes a las equinocandinas

<p><strong>Introducción</strong>: La infección por levaduras del género <em>Candida</em> representa la causa más común de infecciones fúngicas invasivas. Su alta incidencia y la creciente resistencia frente a los azoles y, recientemente, a las equinocandinas ha generado la necesidad de buscar nuevas alternativas farmacológicas. Esta revisión presenta las principales alternativas farmacológicas en estudio frente a <em>Candida</em> resistente a equinocandinas. <strong>Métodos</strong>: Se buscó literatura referente al tema en las bases de datos Bireme, Clinical Key, Embase, Cochrane, Lilacs, Pubmed y Scopus. Se incluyeron 15 artículos en esta revisión. <strong>Resultados</strong>: Se exploran diferentes alternativas, incluyendo el aumento de dosis de las equinocandinas, su combinación con otros medicamentos y nuevos compuestos en estudio. <strong>Conclusión</strong>: A pesar de que las infecciones por <em>Candida</em> resistente a equinocandinas aún representan un desafío, dos alternativas farmacológicas se presentan como promisorias: la combinación con medicamentos existentes como el diclofenaco y nuevos compuestos que se encuentran actualmente en fase II de estudios clínicos.</p><p> </p>

Nanolipid Gel of an Antimycotic Drug for Treating Vulvovaginal Candidiasis-Development and Evaluation

This paper focuses on the development and evaluation of mucoadhesive vaginal gel of fluconazole using nanolipid carriers to enhance tissue deposition in treating vulvovaginal candidiasis. Treatment of vulvovaginal candidiasis includes antimycotic agents prescribed for 1 to 7 days or longer, in relapse either orally or topically. The delivery of fluconazole as nanolipid carriers in vaginal gel can be proposed as suitable alternative to the existing conventional formulations to improve the patient acceptability, compliance and localized drug action. The nanolipid carriers of fluconazole were prepared by phase inversion temperature technique and incorporated into Carbopol 974P as gelling polymer. GRAS excipients selected and optimized were Precirol ATO 5, oleic acid and Kolliphor RH 40 to produce nanolipid dispersions. Stable nanolipid dispersions were developed using sodium dodecyl sulfate as the charge inducer. The optimized nanolipid dispersion of fluconazole had particle size, polydispersity index and zeta potential value of 158.33 ± 2.55 nm, 0.278 ± 0.003 and - 27.33 ± 0.40 mV, respectively and the average entrapment of fluconazole in the lipid carriers was found to be 67.24 ± 0.87%. The optimized vaginal gel had satisfactory mucoadhesive strength and rheological properties to facilitate vaginal application. The fluconazole release from the gel was sustained showing 30.69 ± 1.02% drug deposition in the porcine vaginal mucosa at the end of 8 h with improved antifungal activity against Candida albicans during well diffusion studies. The optimized gel was non-irritant to the vaginal mucosa of female Wistar rats with no signs of erythema or edema.

Macroalgae Extracts From Antarctica Have Antimicrobial and Anticancer Potential

Background: Macroalgae are sources of bioactive compounds due to the large number of secondary metabolites they synthesize. The Antarctica region is characterized by extreme weather conditions and abundant aggregations of macroalgae. However, current knowledge on their biodiversity and their potential for bio-prospecting is still fledging. This study evaluates the antimicrobial and cytotoxic activity of different extracts of four macroalgae (Cystosphaera jacquinotii, Iridaea cordata, Himantothallus grandifolius, and Pyropia endiviifolia) from the Antarctic region against cancer and non-cancer cell lines.

Methods: The antimicrobial activity of macroalgae was evaluated by the broth microdilution method. Extracts were assessed against Staphylococcus aureus ATCC 19095, Enterococcus faecalis ATCC 4083, Escherichia coli ATCC29214, Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 62342, and the clinical isolates from the human oral cavity, namely, C. albicans (3), C. parapsilosis, C. glabrata, C. lipolytica, and C. famata. Cytotoxicity against human epidermoid carcinoma (A-431) and mouse embryonic fibroblast (NIH/3T3) cell lines was evaluated with MTT colorimetric assay.

Results: An ethyl acetate extract of H. grandifolius showed noticeable antifungal activity against all fungal strains tested, including fluconazole-resistant samples. Cytotoxicity investigation with a cancer cell line revealed that the ethyl acetate extract of I. cordata was highly cytotoxic against A-431 cancer cell line, increasing the inhibitory ratio to 91.1 and 95.6% after 24 and 48 h exposure, respectively, for a concentration of 500 μg mL⁻¹. Most of the algal extracts tested showed little or no cytotoxicity against fibroblasts.

Conclusion: Data suggest that macroalgae extracts from Antarctica may represent a source of therapeutic agents.

HIGHLIGHTS

Different macroalgae samples from Antarctica were collected and the lyophilized biomass of each macroalgae was extracted sequentially with different solvents

The antimicrobial and anticancer potential of macroalgae extracts were evaluated

Ethyl acetate extract of H. grandifolius showed noticeable antifungal activity against all the fungal strains tested, including fluconazole-resistant samples

Ethyl acetate extract of I. cordata was highly cytotoxic against the A-431 cancer cell line

Most of the algal extracts tested showed little or no cytotoxicity against normal cell lines

Species-specific detection of Candida tropicalis using evolutionary conserved intein DNA sequences

Inteins (internal proteins) are self-splicing transportable genetic elements present in conserved regions of housekeeping genes. The study highlights the importance of intein as a potential diagnostic marker for species-specific identification of Candida tropicalis, a rapidly emerging opportunistic human pathogen. Initial steps of primer validation, sequence alignment, phylogenetic tree analysis, gel electrophoresis and real-time polymerase chain reaction (PCR) assays were performed to confirm the specificity of the designed primers. The primers were selective for C. tropicalis with 100% inclusivity and showed no cross-species or cross-genera matches. The established technique is a prototype for developing multifaceted PCR assays and for point-of-care testing in near future.

SIGNIFICANCE AND IMPACT OF THE STUDY

Development of molecular markers for specific detection of microbial pathogens using real-time polymerase chain reaction (PCR) is an appealing and challenging technique. A real-time PCR is an emerging technology frequently used to detect the aetiologic agents. In recent times, designing species-specific primers for pathogen detection is gaining momentum. The method offers rapid, accurate and cost-effective strategy to identify the target, thus providing sufficient time to instigate appropriate chemotherapy. The study highlights the use of intein DNA sequence as molecular markers for species-specific identification of Candida tropicalis. The study also offers a prototype model for developing multifaceted PCR assays using intein DNA sequences, and provides a developmental starting point for point-of-care testing in near future.

Candidacidal Activity of a Novel Killer Toxin from Wickerhamomyces anomalus against Fluconazole-Susceptible and -Resistant Strains

The isolation and characterization from the sand fly Phlebotomus perniciosus of a Wickerhamomyces anomalus yeast strain (Wa1F1) displaying the killer phenotype was recently reported. In the present work, the killer toxin (KT) produced by Wa1F1 was purified and characterized, and its antimicrobial activity in vitro was investigated against fluconazole- susceptible and -resistant clinical isolates and laboratory strains of Candida albicans and C. glabrata displaying known mutations. Wa1F1-KT showed a differential killing ability against different mutant strains of the same species. The results may be useful for the design of therapeutic molecules based on Wa1F1-KT and the study of yeast resistance mechanisms.

Plant phenolics and terpenoids as adjuvants of antibacterial and antifungal drugs

BACKGROUND

The intensive use of antibacterial and antifungal drugs has dramatically increased the microbial resistance and has led to a higher number of difficult-to-eradicate infections. Combination therapy with two or more antimicrobial drugs has emerged some years ago to overcome the issue, but it has proven to be not completely effective. Natural secondary metabolites of MW ≤ 500 represent promising adjuvants for antimicrobials and have been the object of several researches that have increased in the last two decades.

PURPOSE

The purpose of this Review is to do a literature search of the natural compounds that showed high enhancing capacity of antibacterials' and antifungals' effects against planktonic bacteria and fungi and to analyze which are the natural products most used in combination with a focus on polyphenols and terpenoids.

RESULTS

One hundred of papers were collected for reviewing. Fifty six (56) of them deal with combinations of low MW natural products with antibacterial drugs against planktonic bacteria and forty four (44) on natural products with antifungal drugs against planktonic fungi. Of the antibacterial adjuvants, 41 (73%) were either polyphenols (27; 48%) or terpenes (14; 25%). The remaining 15 papers (27%), deal with different class of natural products. Since most natural potentiators belong to the terpene or phenolic structural types, a more detailed description of the works dealing with these type of compounds is provided here. Bacterial and fungal resistance mechanisms, the modes of action of the main classes of antibacterial and antifungal drugs and the methodologies most used to assess the type of interactions in the combinations were included in the Review too.

CONCLUSIONS AND PERSPECTIVES

Several promising results on the potentiation effects of antifungals' and antibacterials' activities by low MW natural products mainly on polyphenols and terpenes were reported in the literature and, in spite of that most works included only in vitro assays, this knowledge opens a wide range of possibilities for the combination antimicrobial therapy. Further research including in vivo assays and clinical trials are required to determine the relevance of these antimicrobial enhancers in the clinical area and should be the focus of future studies in order to develop new antimicrobial combination agents that overpass the drawbacks of the existing antibiotics and antifungals in clinical use.

Bridging the Gap to Non-toxic Fungal Control: Lupinus-Derived Blad-Containing Oligomer as a Novel Candidate to Combat Human Pathogenic Fungi

The lack of antifungal drugs with novel modes of action reaching the clinic is a serious concern. Recently a novel antifungal protein referred to as Blad-containing oligomer (BCO) has received regulatory approval as an agricultural antifungal agent. Interestingly its spectrum of antifungal activity includes human pathogens such as Candida albicans, however, its mode of action has yet to be elucidated. Here we demonstrate that BCO exerts its antifungal activity through inhibition of metal ion homeostasis which results in apoptotic cell death in C. albicans. HIP HOP profiling in Saccharomyces cerevisiae using a panel of signature strains that are characteristic for common modes of action identified hypersensitivity in yeast lacking the iron-dependent transcription factor Aft1 suggesting restricted iron uptake as a mode of action. Furthermore, global transcriptome profiling in C. albicans also identified disruption of metal ion homeostasis as a potential mode of action. Experiments were carried out to assess the effect of divalent metal ions on the antifungal activity of BCO revealing that BCO activity is antagonized by metal ions such as Mn²⁺, Zn²⁺, and Fe²⁺. The transcriptome profile also implicated sterol synthesis as a possible secondary mode of action which was subsequently confirmed in sterol synthesis assays in C. albicans. Animal models for toxicity showed that BCO is generally well tolerated and presents a promising safety profile as a topical applied agent. Given its potent broad spectrum antifungal activity and novel multitarget mode of action, we propose BCO as a promising new antifungal agent for the topical treatment of fungal infections.

Gallic acid/hydroxypropyl-β-cyclodextrin complex: Improving solubility for application on in vitro/ in vivo Candida albicans biofilms

The aim of this study was to increase the solubility of gallic acid (GA) for the treatment of Candida albicans biofilm, which is very difficult to treat and requires high drug concentrations. Cyclodextrins (CDs) were used for this purpose. Complexes were evaluated by phase-solubility studies, prepared by spray drying and characterized by drug loading, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The complexes were tested on C. albicans biofilm using in vitro and in vivo models. HPβCD formed soluble inclusion complexes with GA. The percentage of GA in GA/HPβCD was 10.8 ± 0.01%. The SEM and DSC analyses confirmed the formation of inclusion complexes. GA/HPβCD maintained the antimicrobial activity of the pure GA. GA/HPβCD was effective on C. albicans biofilms of 24 and 48h. The in vivo results showed an anti-inflammatory activity of GA/HPβCD with no difference in invading hypha counting among the groups. This study encourages the development of new antifungal agents.

Vetiver Essential Oil in Cosmetics: What Is New?

Background: Vetiver is a key ingredient for the perfume industry nowadays. However, with the constant and rapid changes of personal tastes, this appeal could vanish and this sector could decline quite quickly. New dissemination paths need to be found to tap this valuable resource. Methods: In this way, its potential use in cosmetics either as an active ingredient per se (with cosmeceutical significance or presenting antimicrobial activity) has hence been explored in vitro. Results: In this contribution, we demonstrated that vetiver essential oil displays no particularly significant and innovative cosmetic potential value in formulations apart from its scent already largely exploited. However, evaluated against twenty bacterial strains and two Candida species using the in vitro microbroth dilution method, vetiver oil demonstrated notably some outstanding activities against Gram-positive strains and against one Candida glabrata strain. Conclusions: Based on these findings, vetiver essential oil appears to be an appropriate aspirant for the development of an antimicrobial agent for medicinal purposes and for the development of a cosmetic ingredient used for its scent and displaying antimicrobial activity as an added value.

A pre-therapeutic coating for medical devices that prevents the attachment of Candida albicans

BACKGROUND

Hospital acquired fungal infections are defined as "never events"-medical errors that should never have happened. Systemic Candida albicans infections results in 30-50% mortality rates. Typically, adhesion to abiotic medical devices and implants initiates such infections. Efficient adhesion initiates formation of aggressive biofilms that are difficult to treat. Therefore, inhibitors of adhesion are important for drug development and likely to have a broad spectrum efficacy against many fungal pathogens. In this study we further the development of a small molecule, Filastatin, capable of preventing C. albicans adhesion. We explored the potential of Filastatin as a pre-therapeutic coating of a diverse range of biomaterials.

METHODS

Filastatin was applied on various biomaterials, specifically bioactive glass (cochlear implants, subcutaneous drug delivery devices and prosthetics); silicone (catheters and other implanted devices) and dental resin (dentures and dental implants). Adhesion to biomaterials was evaluated by direct visualization of wild type C. albicans or a non-adherent mutant edt1 -/- that were stained or fluorescently tagged. Strains grown overnight at 30 °C were harvested, allowed to attach to surfaces for 4 h and washed prior to visualization. The adhesion force of C. albicans cells attached to surfaces treated with Filastatin was measured using Atomic Force Microscopy. Effectiveness of Filastatin was also demonstrated under dynamic conditions using a flow cell bioreactor. The effect of Filastatin under microfluidic flow conditions was quantified using electrochemical impedance spectroscopy. Experiments were typically performed in triplicate.

RESULTS

Treatment with Filastatin significantly inhibited the ability of C. albicans to adhere to bioactive glass (by 99.06%), silicone (by 77.27%), and dental resin (by 60.43%). Atomic force microcopy indicated that treatment with Filastatin decreased the adhesion force of C. albicans from 0.23 to 0.017 nN. Electrochemical Impedance Spectroscopy in a microfluidic device that mimic physiological flow conditions in vivo showed lower impedance for C. albicans when treated with Filastatin as compared to untreated control cells, suggesting decreased attachment. The anti-adhesive properties were maintained when Filastatin was included in the preparation of silicone materials.

CONCLUSION

We demonstrate that Filastatin treated medical devices prevented adhesion of Candida, thereby reducing nosocomial infections.

Transcriptional Responses of Candida albicans to Antimicrobial Peptide MAF-1A

Candida albicans is a major fungal pathogen in humans. Novel antifungal agents are urgent demanded due to the challenges of the resistance. Antimicrobial peptides (AMPs) are critical components of the innate immune system against pathogenic microorganism infection. MAF-1A is a novel cationic AMP that comes from Musca domestica and is effective against C. albicans, but the antifungal mechanism remains unclear. In this study, we performed a transcriptomics analysis in C. albicans using RNA-seq technique under the treatment of MAF-1A. A total of 5654 genes were identified. Among these, 1032 were differentially expressed genes (DEGs), including 575 up-regulated genes and 457 down-regulated genes. In these DEGs, genes encoding ergosterol metabolism and fatty acid biosynthesis were identified to be significantly down-regulated, while genes associated with oxidative stress response and cell wall were identified to be significantly up-regulated. Using pathway enrichment analysis, 12 significant metabolic pathways were identified, and ribosome, oxidative phosphorylation, citrate cycle were mainly involved. The results revealed that MAF-1A induces complex responses in C. albicans. This study provides evidence that MAF-1A may inhibit the growth through affect multi-targets in C. albicans cells.

Enhancement of the Efficacy of Photodynamic Inactivation of Candida albicans with the Use of Biogenic Gold Nanoparticles

This study reports on successful photodynamic inactivation of planktonic and biofilm cells of Candida albicans using Rose Bengal (RB) in combination with biogenic gold nanoparticles synthesized by the cell-free filtrate of Penicillium funiculosum BL1 strain. Monodispersed colloidal gold nanoparticles coated with proteins were characterized by a number of techniques including SEM-EDS, TEM, UV-Vis absorption and fluorescence spectroscopy, as well as Fourier transform infrared spectroscopy to be 24 ± 3 nm spheres. A Xe lamp (output power of 20mW, delivering intensity of 53 mW cm^-2 ) was used as a light source to study the effects of RB alone, the gold nanoparticles alone and the RB-gold nanoparticle mixture on the viability of C. albicans cells. The most effective reduction in the number of planktonic cells was found after 30 min of Xe lamp light irradiation (95.4 J cm^-2 ) and was 4.89 log₁₀ that is 99.99% kill for the mixture of RB with gold nanoparticles compared with 2.19 log₁₀ or 99.37% for RB alone. The biofilm cells were more resistant to photodynamic inactivation, and the highest effective reduction in the number of cells was found after 30 min of irradiation in the presence of the RB-gold nanoparticles mixture and was 1.53 log₁₀ , that is 97.04% kill compared with 0.6 log₁₀ or 74.73% for RB. The probable mechanism of enhancement of RB-mediated photodynamic fungicidal efficacy against C. albicans in the presence of biogenic gold nanoparticles is discussed leading to the conclusion that this process may have a multifaceted character.

Quantitation of ergosterol content and gene expression profile of ERG11 gene in fluconazole-resistant Candida albicans

Background and Purpose:

The frequency of opportunistic fungal infections in immunocompromised patients, especially by Candida species, has sharply increased in the last few decades. The objective of this study was to analyse the ergosterol content and gene expression profiling of clinical isolates of fluconazole-resistant Candida albicans.

Materials and Methods:

Sixty clinical samples were identified and collected from immunocompromised patients, namely recurrent oral, vaginal, and cutaneous candidiasis, during 2015-16. Antifungal susceptibility testing of fluconazole against clinical Candida species was performed according to Clinical and Laboratory Standards Institute guidelines. Ergosterol content and gene expression profiling of sterol 14α-demethylase (ERG11) gene in fluconazole-susceptible and –resistant C. albicans were investigated.

Results:

The specimens consisted of C. albicans (46.67%), Candida krusei (41.67%), and Candida tropicalis (11.67%). All the isolates were resistant to fluconazole. No significant reduction was noted in total cellular ergosterol content in comparison with untreated controls in terms of fluconazole-resistant C. albicans. The expressionlevel of ERG11 gene was down-regulated in fluconazole-susceptible C. albicans. Eventually, the expression pattern of ERG11 gene revealed no significant changes in fluconazole-resistant isolates compared to untreated controls. The results revealed no significant differences between fluconazole-susceptible and –resistant C. albicans sequences by comparison with ERG11 reference sequence.

Conclusion:

Our findings provide an insight into the mechanism of fluconazole resistance in C. albicans. The mechanisms proposed for clinical isolates of fluconazole-resistant C. albicans are alteration in sterol biosynthesis, analysis of expression level of ERG11 gene, and analysis of gene sequences. Nonetheless, further studies are imperative to find molecular mechanisms that could be targeted to control fluconazole resistance.

Caspofungin MIC Distribution amongst Commonly Isolated Candida Species in a Tertiary Care Centre - An Indian Experience

INTRODUCTION

Emergence of Candida species resistant to Amphotericin B and triazole has led to use of echinocandins, mostly caspofungin in the management of invasive candidiasis. There are some published reports of caspofungin resistance in Candida species yet no studies on caspofungin susceptibility pattern of Candida species exist in Indian setup.

AIM

To carry out the antifungal susceptibility of Candida isolates against caspofungin.

MATERIALS AND METHODS

In a retrospective study at a tertiary care teaching hospital, 60 preserved Candida isolates from inpatients of invasive candidiasis obtained over a period of 6 months from January 2015 to June 2015 were subjected to antifungal susceptibility to caspofungin and the Minimum Inhibitory Concentrations (MICs) of Candida species to caspofungin were determined by Epsilometer test (E-test).

RESULTS

Thirty Candida albicans and 30 Non albicansCandida mainly Candida glabrata, Candida parapsilosis and Candida tropicalis were tested for caspofungin susceptibitity by E-test. Caspofungin resistance was detected in 6.67% Candida albicans isolates. Caspofungin resistance was not observed in Candida parapsilosis, Candida glabrata and Candida tropicalis. This shows that caspofungin resistance is still rare. Further elaborate studies with clinical correlation data are needed to detect prevalence of caspofungin resistance.

CONCLUSION

Emergence of resistance in our study warrants need of elaborate studies with clinical correlation data to detect prevalence of resistance to caspofungin. E-test method proved to be an easy and simple technique for testing susceptibility of Candida to caspofungin.

Antibiotic Resistant Superbugs: Assessment of the Interrelationship of Occurrence in Clinical Settings and Environmental Niches

The increasing threat to global health posed by antibiotic resistance remains of serious concern. Human health remains at higher risk due to several reported therapeutic failures to many life threatening drug resistant microbial infections. The resultant effects have been prolonged hospital stay, higher cost of alternative therapy, increased mortality, etc. This opinionated review considers the two main concerns in integrated human health risk assessment (i.e., residual antibiotics and antibiotic resistant genes) in various compartments of human environment, as well as clinical dynamics associated with the development and transfer of antibiotic resistance (AR). Contributions of quorum sensing, biofilms, enzyme production, and small colony variants in bacteria, among other factors in soil, water, animal farm and clinical settings were also considered. Every potential factor in environmental and clinical settings that brings about AR needs to be identified for the summative effects in overall resistance. There is a need to embrace coordinated multi-locational approaches and interrelationships to track the emergence of resistance in different niches in soil and water versus the hospital environment. The further integration with advocacy, legislation, enforcement, technological innovations and further research input and recourse to WHO guidelines on antibiotic policy would be advantageous towards addressing the emergence of antibiotic resistant superbugs.

Blad-Containing Oligomer Fungicidal Activity on Human Pathogenic Yeasts. From the Outside to the Inside of the Target Cell

Blad polypeptide comprises residues 109-281 of Lupinus albus β-conglutin precursor. It occurs naturally as a major subunit of an edible, 210 kDa oligomer which accumulates to high levels, exclusively in the cotyledons of Lupinus seedlings between the 4th and 14th day after the onset of germination. Blad-containing oligomer (BCO) exhibits a potent and broad spectrum fungicide activity toward plant pathogens and is now on sale in the US under the tradename FractureTM. In this work we demonstrate its antifungal activity toward human pathogens and provide some insights on its mode of action. BCO bioactivity was evaluated in eight yeast species and compared to that of amphotericin B (AMB). BCO behaved similarly to AMB in what concerns both cellular inhibition and cellular death. As a lectin, BCO binds strongly to chitin. In addition, BCO is known to possess 'exochitinase' and 'endochitosanase' activities. However, no clear disruption was visualized at the cell wall after exposure to a lethal BCO concentration, except in cell buds. Immunofluorescent and immunogold labeling clearly indicate that BCO enters the cell, and membrane destabilization was also demonstrated. The absence of haemolytic activity, its biological origin, and its extraordinary antifungal activity are the major outcomes of this work, and provide a solid background for a future application as a new antifungal therapeutic drug. Furthermore, its predictable multisite mode of action suggests a low risk of inducing resistance mechanisms, which are now a major problem with other currently available antifungal drugs.

Sticky Situation: An Investigation of Robust Aqueous-Based Recombinant Spider Silk Protein Coatings and Adhesives

The mechanical properties and biocompatibility of spider silks have made them one of the most sought after and studied natural biomaterials. A biomimetic process has been developed that uses water to solvate purified recombinant spider silk proteins (rSSps) prior to material formation. The absence of harsh organic solvents increases cost effectiveness, safety, and decreases the environmental impact of these materials. This development allows for the investigation of aqueous-based rSSps as coatings and adhesives and their potential applications. In these studies it was determined that fiber-based rSSps in nonfiber formations have the capability to coat and adhere numerous substrates, whether rough, smooth, hydrophobic, or hydrophilic. Further, these materials can be functionalized for a variety of processes. Drug-eluting coatings have been made with the capacity to release a variety of compounds in addition to their inherent ability to prevent blood clotting and biofouling. Additionally, spider silk protein adhesives are strong enough to outperform some conventional glues and still display favorable tissue implantation properties. The physical properties, corresponding capabilities, and potential applications of these nonfibrous materials were characterized in this study. Mechanical properties, ease of manufacturing, biodegradability, biocompatibility, and functionality are the hallmarks of these revolutionary spider silk protein materials.

Evolution and Application of Inteins in Candida species: A Review

Inteins are invasive intervening sequences that perform an autocatalytic splicing from their host proteins. Among eukaryotes, these elements are present in many fungal species, including those considered opportunistic or primary pathogens, such as Candida spp. Here we reviewed and updated the list of Candida species containing inteins in the genes VMA, THRRS and GLT1 and pointed out the importance of these elements as molecular markers for molecular epidemiological researches and species-specific diagnosis, since the presence, as well as the size of these inteins, is polymorphic among the different species. Although absent in Candida albicans, these elements are present in different sizes, in some environmental Candida spp. and also in most of the non-albicans Candida spp. considered emergent opportunistic pathogens. Besides, the possible role of these inteins in yeast physiology was also discussed in the light of the recent findings on the importance of these elements as post-translational modulators of gene expression, reinforcing their relevance as alternative therapeutic targets for the treatment of non-albicans Candida infections, because, once the splicing of an intein is inhibited, its host protein, which is usually a housekeeping protein, becomes non-functional.

Quinone derivatives isolated from the endolichenic fungus Phialocephala fortinii are Mdr1 modulators that combat azole resistance in Candida albicans

One of the main azole-resistance mechanisms in Candida pathogens is the upregulation of drug efflux pumps, which compromises the efficacy of azoles and results in treatment failure. The combination of azole-antifungal agents with efflux pump inhibitors represents a promising strategy to combat fungal infection. High-throughput screening of 150 extracts obtained from endolichenic fungal cultures led to the discovery that the extract of Phialocephala fortinii exhibits potent activity for the reversal of azole resistance. From P. fortinii cultures, a total of 15 quinone derivatives, comprising 11 new derivatives and 4 known compounds, were obtained. Among these compounds, palmarumycin P3 (3) and phialocephalarin B (8) specifically modulate the expression of MDR1 to inhibit the activity of drug efflux pumps and therefore reverse azole resistance. The present study revealed Mdr1 targeting as an alternative mechanism for the discovery of new agents to fight antifungal drug resistance.

Activity of crude extracts from Brazilian cerrado plants against clinically relevant Candida species

Background

Medicinal plants have traditionally been used in many parts of the world as alternative medicine. Many extracts and essential oils isolated from plants have disclosed biological activity, justifying the investigation of their potential antimicrobial activity. In this study, the in vitro antifungal activity of six Brazilian Cerrado medicinal plant species were evaluated against clinically relevant Candida species.

Methods

The crude extract plants were evaluated against American Type Culture Collection (ATCC) standard strains of Candida spp. using disk diffusion method and determining the minimum inhibitory concentration (MIC). The chemical study results were confirmed by HPLC method.

Results

All six plant species showed antifungal activity. Among the species studied, Eugenia dysenterica and Pouteria ramiflora showed significant inhibitory activity against C. tropicalis at lowest MIC value of 125 and 500 μg/disc, respectively. The Eugenia dysenterica also disclosed MIC value of 125 μg/disc against C. famata, 250 μg/disc against C. krusei and 500 μg/disc against C. guilliermondii and C. parapsilosis. Pouteria torta, Bauhinia rufa, Erythroxylum daphnites and Erythroxylum subrotundum showed activity against the yeast strains with MIC value of 1000 μg/disc. The chemical study of the most bioactive extracts of Eugenia dysenterica and Pouteria ramiflora revealed catechin derivatives and flavonoids as main components.

Conclusions

All six evaluated plant species showed good antifungal potential against several Candida strains. However, E .dysenterica and P. ramiflora showed the higher inhibitory effect against the non-albicans Candida species. Our results may contribute to the continuing search of new natural occurring products with antifungal activity.

Lactobacillus acidophilus ATCC 4356 inhibits biofilm formation by C. albicans and attenuates the experimental candidiasis in Galleria mellonella

Probiotic strains of Lactobacillus have been studied for their inhibitory effects on Candida albicans. However, few studies have investigated the effect of these strains on biofilm formation, filamentation and C. albicans infection. The objective of this study was to evaluate the influence of Lactobacillus acidophilus ATCC 4356 on C. albicans ATCC 18804 using in vitro and in vivo models. In vitro analysis evaluated the effects of L. acidophilus on the biofilm formation and on the capacity of C. albicans filamentation. For in vivo study, Galleria mellonella was used as an infection model to evaluate the effects of L. acidophilus on candidiasis by survival analysis, quantification of C. albicans CFU/mL, and histological analysis. The direct effects of L. acidophilus cells on C. albicans, as well as the indirect effects using only a Lactobacillus culture filtrate, were evaluated in both tests. The in vitro results showed that both L. acidophilus cells and filtrate were able to inhibit C. albicans biofilm formation and filamentation. In the in vivo study, injection of L. acidophilus into G. mellonella larvae infected with C. albicans increased the survival of these animals. Furthermore, the number of C. albicans CFU/mL recovered from the larval hemolymph was lower in the group inoculated with L. acidophilus compared to the control group. In conclusion, L. acidophilus ATCC 4356 inhibited in vitro biofilm formation by C. albicans and protected G. mellonella against experimental candidiasis in vivo.

Taxonomy of Allergenic Fungi

The Kingdom Fungi contains diverse eukaryotic organisms including yeasts, molds, mushrooms, bracket fungi, plant rusts, smuts, and puffballs. Fungi have a complex metabolism that differs from animals and plants. They secrete enzymes into their surroundings and absorb the breakdown products of enzyme action. Some of these enzymes are well-known allergens. The phylogenetic relationships among fungi were unclear until recently because classification was based on the sexual state morphology. Fungi lacking an obvious sexual stage were assigned to the artificial, now-obsolete category, "Deuteromycetes" or "Fungi Imperfecti." During the last 20 years, DNA sequencing has resolved 8 fungal phyla, 3 of which contain most genera associated with important aeroallergens: Zygomycota, Ascomycota, and Basidiomycota. Advances in fungal classification have required name changes for some familiar taxa. Because of regulatory constraints, many fungal allergen extracts retain obsolete names. A major benefit from this reorganization is that specific immunoglobulin E (IgE) levels in individuals sensitized to fungi appear to closely match fungal phylogenetic relationships. This close relationship between molecular fungal systematics and IgE sensitization provides an opportunity to systematically look at cross-reactivity and permits representatives from each taxon to serve as a proxy for IgE to the group.

Oropharyngeal candidiasis in children with lymphohematopoietic malignancies in Mashhad, Iran

Background and Purpose:

Over the past years, the role of fungi as a cause of nosocomial infections in hospitalized patients has been accentuated. Candida species constitute an important group of fungi causing diseases in immunocompromised patients. Oropharyngeal candidiasis continues to be a prevalent infection in immunodeficient patients. In this study, we aimed to determine the incidence of oropharyngeal candidiasis in children with lymphohematopoietic malignancies.

Materials and Methods:

In total, 102 patients with lymphohematopoietic malignancies and 50 healthy controls were examined in terms of Candida infections via direct sampling of the oropharyngeal cavity. Fresh smears were prepared with 10% potassium hydroxide and Gram staining was carried out. Subsequently, the obtained specimens were cultured on Sabouraud dextrose agar for further analysis.

Results:

The most common Candida species were Candida albicans (31%), other non-C. albicans species (14.7%), C. glabrata (6.8%), and C. krusei (0.98%) in the case group, while in the control group, other non-C. albicans species (10%) and C. albicans (8%) were the most common species.

Conclusion:

In the present study, Candida species were the most common fungal pathogens in pediatric cancer patients; therefore, efforts should be made to prevent fungemia and fungal pneumonia. Also, non-C. albicans species must be considered as a new risk factor for pediatric cancer patients.

Detection of inhibitors of Candida albicans Cdr transporters using a diS-C3(3) fluorescence

Candida albicans is a major cause of opportunistic and life-threatening, systemic fungal infections. Hence new antifungal agents, as well as new methods to treat fungal infections, are still needed. The application of inhibitors of drug-efflux pumps may increase the susceptibility of C. albicans to drugs. We developed a new fluorescence method that allows the in vivo activity evaluation of compounds inhibiting of C. albicans transporters. We show that the potentiometric dye 3,3′-dipropylthiacarbocyanine iodide diS-C₃(3) is pumped out by both Cdr1 and Cdr2 transporters. The fluorescence labeling with diS-C₃(3) enables a real-time observation of the activity of C. albicans Cdr1 and Cdr2 transporters. We demonstrate that enniatin A and beauvericin show different specificities toward these transporters. Enniatin A inhibits diS-C₃(3) efflux by Cdr1 while beauvericin inhibits both Cdr1p and Cdr2p.

Molecular identification and in-vitro antifungal susceptibility testing of Candida species isolated from patients with onychomycosis

BACKGROUND AND PURPOSE

Candida species are the most opportunistic fungi affecting the nails and resulting in onychomycosis. In this study, we identified and evaluated in-vitro susceptibility of the recovered isolates against fluconazole (FLC), voriconazole (VRC), and clotrimazole (CLT) using the Clinical and Laboratory Standards Institute (CLSI) M27-A3 document.

MATERIALS AND METHODS

From patients with either clinically or mycologically proven onychomycosis, 97 isolates comprising of seven Candida species were isolated, which were identified by both conventional and molecular techniques such as polymerase chain reaction-restriction fragment length polymorphism. In addition, Candida dubliniensis was confirmed by restriction endonuclease analysis. Antifungal susceptibility of each isolate against the three azoles applied in this study was determined using the CLSI microdilution reference method M27-A3.

RESULTS

Candida parapsilosis(C. parapsilosis) was the most frequently isolated species (n=44), followed by C. albicans (n=23), C.tropicalis (n=13), C.glabrata (n=7), C.krusei (n=6), C.guilliermondii (n=3), and C. dubliniensis (n=1). All the isolates were susceptible to CLT. VRC had lower minimum inhibitory concentration (MIC) values for the isolates compared to FLC. Geometric mean MIC values of VRC, FLC, and CLT for C. parapsilosis isolates were 0.07 μg/ml, 0.8 μg/ml, and 0.35 μg/ml, respectively. Collectively, all species exhibited greater susceptibility to VRC in comparison to C. albicans (P≤0.001).

CONCLUSION

This study showed that non-albicansCandida species were the most common etiologic agents of non-dermatophyte onychomycosis. The major antifungal agents used in clinics to empirically treat yeast onychomycosis are FLC and CLT. Our data suggested that CLT is a better choice for the treatment of Candida onychomycosis, especially in drug resistant cases.

Fungicidal mechanisms of the antimicrobial peptide Bac8c

Bac8c (RIWVIWRR-NH2) is an analogue peptide derived through complete substitution analysis of the linear bovine host defense peptide variant Bac2A. In the present study, the antifungal mechanism of Bac8c against pathogenic fungi was investigated, with a particular focus on the effects of Bac8c on the cytoplasmic membrane. We used bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)] staining and 3,3'-dipropylthiacarbocyanine iodide [DiSC3(5)] assays to show that Bac8c induced disturbances in the membrane potential of Candida albicans. An increase in membrane permeability and suppression of cell wall regeneration were also observed in Bac8c-treated C. albicans. We studied the effects of Bac8c treatment on model membranes to elucidate its antifungal mechanism. Using calcein and FITC-labeled dextran leakage assays from Bac8c-treated large unilamellar vesicles (LUVs) and giant unilamellar vesicles (GUVs), we found that Bac8c has a pore-forming action on fungal membranes, with an estimated pore radius of between 2.3 and 3.3 nm. A membrane-targeted mechanism of action was also supported by the observation of potassium release from the cytosol of Bac8c-treated C. albicans. These results indicate that Bac8c is considered as a potential candidate to develop a novel antimicrobial agent because of its low-cost production characteristics and high antimicrobial activity via its ability to induce membrane perturbations in fungi.

Resistance of Candida spp. to antifungal drugs in the ICU: where are we now?

Current increases in antifungal drug resistance in Candida spp. and clinical treatment failures are of concern, as invasive candidiasis is a significant cause of mortality in intensive care units (ICUs). This trend reflects the large and expanding use of newer broad-spectrum antifungal agents, such as triazoles and echinocandins. In this review, we firstly present an overview of the mechanisms of action of the drugs and of resistance in pathogenic yeasts, subsequently focusing on recent changes in the epidemiology of antifungal resistance in ICU. Then, we emphasize the clinical impacts of these current trends. The emergence of clinical treatment failures due to resistant isolates is described. We also consider the clinical usefulness of recent advances in the interpretation of antifungal susceptibility testing and in molecular detection of the mutations underlying acquired resistance. We pay particular attention to practical issues relating to ICU patient management, taking into account the growing threat of antifungal drug resistance.

Analysis of the protein domain and domain architecture content in fungi and its application in the search of new antifungal targets

Over the past several years fungal infections have shown an increasing incidence in the susceptible population, and caused high mortality rates. In parallel, multi-resistant fungi are emerging in human infections. Therefore, the identification of new potential antifungal targets is a priority. The first task of this study was to analyse the protein domain and domain architecture content of the 137 fungal proteomes (corresponding to 111 species) available in UniProtKB (UniProt KnowledgeBase) by January 2013. The resulting list of core and exclusive domain and domain architectures is provided in this paper. It delineates the different levels of fungal taxonomic classification: phylum, subphylum, order, genus and species. The analysis highlighted Aspergillus as the most diverse genus in terms of exclusive domain content. In addition, we also investigated which domains could be considered promiscuous in the different organisms. As an application of this analysis, we explored three different ways to detect potential targets for antifungal drugs. First, we compared the domain and domain architecture content of the human and fungal proteomes, and identified those domains and domain architectures only present in fungi. Secondly, we looked for information regarding fungal pathways in public repositories, where proteins containing promiscuous domains could be involved. Three pathways were identified as a result: lovastatin biosynthesis, xylan degradation and biosynthesis of siroheme. Finally, we classified a subset of the studied fungi in five groups depending on their occurrence in clinical samples. We then looked for exclusive domains in the groups that were more relevant clinically and determined which of them had the potential to bind small molecules. Overall, this study provides a comprehensive analysis of the available fungal proteomes and shows three approaches that can be used as a first step in the detection of new antifungal targets.

Some fungi have become pathogenic to plants and in a lesser extent to animals. Under certain conditions their presence in the human body can prove a threat for human health, especially for immunocompromised patients. Yet, some fungi can also infect healthy individuals. The low sensitivity of the antifungal drugs available together with the clinically observed resistance of some fungi raises the demand for new alternative treatments. Proteins are biological molecules which perform essential functions within the living organisms. Many of those functions are attributed to the varying folded structure of each protein. These configurations are composed of functional units -also called domains- each one independently responsible for a fraction of the overall biological function. Understanding how the different block combinations are distributed across members of the same or similar families of organisms is important. For instance, exclusive domain combinations can hold particular acquired functions. Blocks displaying a high mobility can play major roles for the organism's survival. The biological goal of this study was to analyse the functional implications of protein domains and domain combinations in the available fungal proteomes. This information can be used to highlight proteins and pathways that could be potentially used as drug targets.

In vitro and in vivo antifungal activities of selected Cameroonian dietary spices

Background

Spices and herbs have been used in food since ancient times to give taste and flavor and also as food preservatives and disease remedies. In Cameroon, the use of spices and other aromatic plants as food flavoring is an integral part of dietary behavior, but relatively little is known about their antifungal potential.

The present work was designed to assess the antifungal properties of extracts from spices used in Cameroonian dietary.

Methods

The in vitro antifungal activities of twenty three extracts from twenty one spices were assessed by the broth micro-dilution method against eight fungi. Also, the in vivo activity of Olax subscorpioidea extract (the most active extract) was evaluated in rat model of disseminated candidiasis due to Candida albicans by estimating the fungal burden in blood and kidney.

Results

Seven extracts (30%) exhibited moderate to significant antifungal activities, inhibiting the growth of the microorganisms at concentrations ranging from 0.048 to 0.39 mg/mL. Olax subscorpioidea extract exhibited the highest antifungal activity particularly against Candida albicans and Candida tropicalis (MIC of 0.097 mg/mL and 0.048 mg/mL respectively). Sixteen extracts (70%) were weakly active (MICs > 6.25 mg/mL). Oral administration of O. subscorpioidea extract at the dose 2 g/kg of body weight (bw) to artificially infected rats revealed a drop in the number of colony forming units per milliliter (cfu/mL) of Candida albicans cells in the blood below the detection limit (100 cfu/mL) while a modest decrease was observed in the kidney.

Conclusion

The present work shows that some of the spices studied possess interesting antifungal properties and could be used to treat candidiasis. Among the plant species tested, Olax subscorpioidea displayed the most promising result.