Antimicrobial resistance: resistance to antifungal agents: mechanisms and clinical impact

Fungal keratitis: Mechanisms of infection and management strategies

Fungal corneal ulcers are an uncommon, yet challenging, cause of vision loss. In the United States, geographic location appears to dictate not only the incidence of fungal ulcers, but also the fungal genera most encountered. These patterns of infection can be linked to environmental factors and individual characteristics of fungal organisms. Successful management of fungal ulcers is dependent on an early diagnosis. New diagnostic modalities like confocal microscopy and polymerase chain reaction are being increasingly used to detect and identify infectious organisms. Several novel therapies, including crosslinking and light therapy, are currently being tested as alternatives to conventional antifungal medications. We explore the biology of Candida, Fusarium, and Aspergillus, the three most common genera of fungi causing corneal ulcers in the United States and discuss current treatment regimens for the management of fungal keratitis.

Update on Candida krusei, a potential multidrug-resistant pathogen

Although Candida albicans remains the main cause of candidiasis, in recent years a significant number of infections has been attributed to non-albicans Candida (NAC) species, including Candida krusei. This epidemiological change can be partly explained by the increased resistance of NAC species to antifungal drugs. C. krusei is a diploid, dimorphic ascomycetous yeast that inhabits the mucosal membrane of healthy individuals. However, this yeast can cause life-threatening infections in immunocompromised patients, with hematologic malignancy patients and those using prolonged azole prophylaxis being at higher risk. Fungal infections are usually treated with five major classes of antifungal agents which include azoles, echinocandins, polyenes, allylamines, and nucleoside analogues. Fluconazole, an azole, is the most commonly used antifungal drug due to its low host toxicity, high water solubility, and high bioavailability. However, C. krusei possesses intrinsic resistance to this drug while also rapidly developing acquired resistance to other antifungal drugs. The mechanisms of antifungal resistance of this yeast involve the alteration and overexpression of drug target, reduction in intracellular drug concentration and development of a bypass pathway. Antifungal resistance menace coupled with the paucity of the antifungal arsenal as well as challenges involved in antifungal drug development, partly due to the eukaryotic nature of both fungi and humans, have left researchers to exploit alternative therapies. Here we briefly review our current knowledge of the biology, pathophysiology and epidemiology of a potential multidrug-resistant fungal pathogen, C. krusei, while also discussing the mechanisms of drug resistance of Candida species and alternative therapeutic approaches.

Impact of antifungal stewardship interventions on the susceptibility of colonized Candida species in pediatric patients with malignancy

There is a worldwide concern regarding the antimicrobial resistance and the inappropriate use of antifungal agents, which had led to an ever-increasing antifungal resistance. This study aimed to identify the antifungal susceptibility of colonized Candida species isolated from pediatric patients with cancer and evaluate the clinical impact of antifungal stewardship (AFS) interventions on the antifungal susceptibility of colonized Candida species. Candida species colonization was evaluated among hospitalized children with cancer in a tertiary teaching hospital, Shiraz 2017–2018. Samples were collected from the mouth, nose, urine, and stool of the patients admitted to our center and cultured on sabouraud dextrose agar. The isolated yeasts identified by polymerase chain reaction–restriction fragment length polymorphisms (PCR–RFLP). DNA Extracted and PCR amplification was performed using the ITS1 and ITS4 primer pairs and Msp I enzyme. The broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) for amphotericin B, caspofungin, and azoles. The prevalence of Candida albicans in the present study was significantly higher than other Candida species. Candida albicans species were completely susceptible to the azoles. The susceptibility rate of C. albicans to amphotericin B and caspofungin was 93.1% and 97.1%, respectively. The fluconazole MIC values of Candida albicans decreased significantly during the post-AFS period (P < 0.001; mean difference: 72.3; 95% CI of the difference: 47.36–98.62). We found that ‏52.5% (53/117) of the isolated C. albicans were azole-resistant before AFS implementation, while only 1.5% (2/102) of the isolates were resistant after implementation of the AFS program (P < 0.001). C. albicans fluconazole and caspofungin resistant rate also decreased significantly (P < 0.001) after implementation of the AFS program [26 (32.9%) versus 0 (0.0%) and 11 (10.9%) versus 1 (0.9%), respectively]. Besides, fluconazole use (p < 0.05) and fluconazole expenditure reduced significantly (about one thousand US$ per year) after the AFS program. Our results confirm the positive effect of optimized antifungal usage and bedside intervention on the susceptibility of Candida species after the implementation of the AFS program. C. albicans and C. glabrata exhibited a significant increase in susceptibility after the execution of the AFS program.

Identification of Thiazoyl Guanidine Derivatives as Novel Antifungal Agents Inhibiting Ergosterol Biosynthesis for Treatment of Invasive Fungal Infections

Invasive fungal infections (IFIs) are fatal infections, but treatment options are limited. The clinical efficacies of existing drugs are unsatisfactory because of side effects, drug-drug interaction, unfavorable pharmacokinetic profiles, and emerging drug-resistant fungi. Therefore, the development of antifungal drugs with a new mechanism is an urgent issue. Herein, we report novel aryl guanidine antifungal agents, which inhibit a novel target enzyme in the ergosterol biosynthesis pathway. Structure-activity relationship development and property optimization by reducing lipophilicity led to the discovery of 6h, which showed potent antifungal activity against Aspergillus fumigatus in the presence of serum, improved metabolic stability, and PK properties. In the murine systemic A. fumigatus infection model, 6h exhibited antifungal efficacy equivalent to voriconazole (1e). Furthermore, owing to the inhibition of a novel target in the ergosterol biosynthesis pathway, 6h showed antifungal activity against azole-resistant A. fumigatus.

Prevalence and mechanisms of azole resistance in clinical isolates of Aspergillus section Fumigati species in a Canadian tertiary care centre, 2000 to 2013

OBJECTIVES

Azole resistance among Aspergillus fumigatus isolates is a growing concern worldwide. Induction of mutations during azole therapy, environment-acquired mutations caused by azole fungicides and intrinsic resistance of cryptic Fumigati species all contribute to the burden of resistance. However, there is a lack of data in Canada on this emerging threat.

METHODS

To gain insights into the magnitude and mechanisms of resistance, a 14 year collection of Aspergillus section Fumigati comprising 999 isolates from 807 patients at a Montreal hospital was screened for azole resistance, and resistance mechanisms were investigated with the combined use of genome sequencing, 3D modelling and phenotypic efflux pump assays.

RESULTS

Overall azole resistance was low (4/807 patients; 0.5%). A single azole-resistant A. fumigatus sensu stricto strain, isolated from a patient with pulmonary aspergillosis, displayed efflux-pump-mediated resistance. Three patients were colonized or infected with azole-resistant cryptic Fumigati species (one Aspergillus thermomutatus, one Aspergillus lentulus and one Aspergillus turcosus). Evidence is presented that azole resistance is efflux-pump-mediated in the A. turcosus isolate, but not in the A. lentulus and A. thermomutatus isolates.

CONCLUSIONS

Azole resistance is rare in our geographic area and currently driven by cryptic Fumigati species. Continued surveillance of emergence of resistance is warranted.

Emerging Prospects for Combating Fungal Infections by Targeting Phosphatidylinositol Transfer Proteins

The emergence of fungal “superbugs” resistant to the limited cohort of anti-fungal agents available to clinicians is eroding our ability to effectively treat infections by these virulent pathogens. As the threat of fungal infection is escalating worldwide, this dwindling response capacity is fueling concerns of impending global health emergencies. These developments underscore the urgent need for new classes of anti-fungal drugs and, therefore, the identification of new targets. Phosphoinositide signaling does not immediately appear to offer attractive targets due to its evolutionary conservation across the Eukaryota. However, recent evidence argues otherwise. Herein, we discuss the evidence identifying Sec14-like phosphatidylinositol transfer proteins (PITPs) as unexplored portals through which phosphoinositide signaling in virulent fungi can be chemically disrupted with exquisite selectivity. Recent identification of lead compounds that target fungal Sec14 proteins, derived from several distinct chemical scaffolds, reveals exciting inroads into the rational design of next generation Sec14 inhibitors. Development of appropriately refined next generation Sec14-directed inhibitors promises to expand the chemical weaponry available for deployment in the shifting field of engagement between fungal pathogens and their human hosts.

Deciphering the epidemiology of invasive candidiasis in the intensive care unit: is it possible?

Invasive candidiasis (IC) has emerged in the last decades as an important cause of morbidity, mortality, and economic load in the intensive care unit (ICU). The epidemiology of IC is still a difficult and unsolved enigma for the literature. Accurate estimation of the true burden of IC is difficult due to variation in definitions and limitations inherent to available case-finding methodologies. Candidemia and intra-abdominal candidiasis (IAC) are the two predominant types of IC in ICU. During the last two decades, an increase in the incidence of candidemia has been constantly reported particularly in the expanding populations of elderly or immunosuppressed patents, with a parallel change in Candida species (spp.) distribution worldwide. Epidemiological shift in non-albicans spp. has reached worrisome trends. Recently, a novel, multidrug-resistant Candida spp., Candida auris, has globally emerged as a nosocomial pathogen causing a broad range of healthcare-associated invasive infections. Epidemiological profile of IAC remains imprecise. Though antifungal drugs are available for Candida infections, mortality rates continue to be high, estimated to be up to 50%. Increased use of fluconazole and echinocandins has been associated with the emergence of resistance to these drugs, which affects particularly C. albicans and C. glabrata. Crucial priorities for clinicians are to recognize the epidemiological trends of IC as well as the emergence of resistance to antifungal agents to improve diagnostic techniques and strategies, develop international surveillance networks and antifungal stewardship programmes for a better epidemiological control of IC.

Ketorolac-fluconazole: A New Combination Reverting Resistance in Candida albicans from Acute Myeloid Leukemia Patients on Induction Chemotherapy: In vitro Study

BACKGROUND AND OBJECTIVES

Candida albicans is a significant source of morbidity and mortality for patients with acute myeloid leukemia (AML). Prolonged use of fluconazole as empirical antifungal prophylaxis in AML patients leads to overexpression of efflux pump genes that resulted in the emergence of azole-resistant species. Consequently, the introduction of a new strategy to improve the management of C. albicans infections is an urgent need. Nonsteroidal anti-inflammatory drug (NSAID) ketorolac is associated with a reduction in cancer relapses. The present study was performed to investigate the use of ketorolac-fluconazole combination to reverse fluconazole resistance in C. albicans isolated from AML patients on induction chemotherapy.

PATIENTS AND METHODS

One hundred and seventy AML patients were evaluated. Fifty C. albicans were isolated and subjected to disc diffusion assay and broth microdilution for fluconazole alone and combined with different concentrations of ketorolac. Efflux pump gene (CDR1, CDR2, and MDR1) expressions were quantified by real-time PCR.

RESULTS

The tested ketorolac acted synergistically with fluconazole against resistant C. albicans with the minimum inhibitory concentration (MIC) of fluconazole decreased from >160 μg/mL to 0.3-1.25 μg/mL in (93.8%) of resistant isolates with fractional inhibitory concentration index (FICI) value of 0.25. The majority of the resistant isolates overexpressed CDR1 (71.1%) and MDR1 (60%).

CONCLUSION

Ketorolac-fluconazole in vitro combination would be a promising strategy for further clinical in vivo trials to overcome fluconazole resistance in AML patients on induction chemotherapy.

Prevalence, species distribution and antifungal susceptibility of Candida albicans causing vaginal discharge among symptomatic non-pregnant women of reproductive age at a tertiary care hospital, Vietnam

Background

Vaginal candidiasis is frequent in women of reproductive age. Accurate identification Candida provides helpful information for successful therapy and epidemiology study; however, there are very limited data from the Vietnam have been reported. This study was performed to determine the prevalence, species distribution of yeast causing vaginal discharge and antifungal susceptibility patterns of Candida albicans among symptomatic non-pregnant women of reproductive age.

Methods

Vaginal discharge samples were collected from 462 women of reproductive age in Hanoi, Vietnam between Sep 2019 and Oct 2020. Vaginal swabs from these patients were examined by direct microscopic examination (10% KOH). CHROMagar™ Candida medium and Sabouraud dextrose agar supplemented with chloramphenicol (0.5 g/l) were used to isolate yeast, and species identification was performed using morphological tests and molecular tools (PCR and sequencing). Antifungal susceptibility testing was determined according to the Clinical and Laboratory Standards Institute guidelines (M27-A3 and M27-S4).

Results

The prevalence of vaginal yeast colonization in non-pregnant women was 51.3% of 462 participants. Nine different yeast species were identified. Among these isolates, C. albicans (51.37%) was the most frequent, followed by C. parapsilosis (25.88%), C. glabrata (11.37%), C. tropicalis (4.31%), C. krusei (3.92%), C. africana (1.57%), Saccharomyces cerevisiae (0.78%), C. nivariensis (1 isolates, 0.39%), and C. lusitaniae (1 isolates, 0.39%), respectively. Among C. albicans, all 46 isolates were 100% susceptible to micafungin, caspofungin, and miconazole. The susceptibility rates to amphotericine B, 5-flucytosine, fluconazole, itraconazole and voriconazole were 95.65, 91.30, 91.30, 82.61 and 86.95%, respectively.

Conclusions

The prevalence of VVC among symptomatic non-pregnant women of reproductive age in Vietnam was higher than many parts of the world. The high frequency of non-albicans Candida species, which were often more resistant to antifungal agents, was a notable feature. Resistance rates of vaginal C. albicans isolates to antifungal agents was low. Our findings suggest that continued surveillance of changes in species distribution and susceptibility to antifungals should be routinely screened and treated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06192-7.

Emerging Issues in Antifungal Resistance

Invasive fungal diseases continue to cause substantial mortality in the enlarging immunocompromised population. It is fortunate that the field has moved past amphotericin B deoxycholate as the only available antifungal drug but despite new classes of antifungal agents both primary and secondary drug resistance in molds and yeasts abound. From the rise of multiple-drug-resistant Candida auris to the agrochemical selection of environmental azole-resistant Aspergillus fumigatus, it is and will be critical to understand antifungal drug resistance and both prevent and treat it with new strategies and agents.

Risks associated with pathogenic fungi isolated from surgical centers, intensive care units, and materials sterilization center in hospitals. Risks associated with pathogenic fungi isolated from critical hospital areas

The hospital environment requires special attention to air quality, since it needs to be healthy for the protection of patients and health professionals in order to prevent them against hospital infections. The objective of this study was to isolate, identify and evaluate the susceptibility profile of isolated fungi from two hospitals. For air sampling the impaction (Spin Air, IUL®) and passive sedimentation methods were used. For the isolation of fungi from surfaces, contact plates (RODAC®) were used. The identification of the fungi was performed by observing the macroscopic and microscopic aspects of the colonies, whereas for better visualization of fruiting structures, the microculture technique was performed on slides. To evaluate the susceptibility profile, the broth microdilution test recommended by CLSI was performed. Thirty-five isolates were identified: Aspergillus flavus (12), Aspergillus fumigatus (11), Aspergillus niger (1), Aspergillus terreus (2), Penicillium spp. (7), and Fusarium spp. (2) in the hospitals evaluated. All isolates had a minimum inhibitory concentration (MIC) more than 128 μg/ml for fluconazole; 0.5 to 4.0 μg/ml for amphotericin B (hospital 1), and all isolates from haospital 2 had MIC ≥2.0 μg/ml. In hospital 1, MIC for posaconazole ranged from 0.25 μg/ml to ≥32 μg/ml, and hospital 2 ranged from 0.5 to 1.0 μg/ml. The monitoring and evaluation of air quality and surfaces are essential measures for prevention and control of hospital infections, as these microorganisms are becoming increasingly resistant to antimicrobial agents, thus making treatment difficult, especially in immunocompromised individuals.

Drug Repurposing in Medical Mycology: Identification of Compounds as Potential Antifungals to Overcome the Emergence of Multidrug-Resistant Fungi

Immunodepression, whether due to HIV infection or organ transplantation, has increased human vulnerability to fungal infections. These conditions have created an optimal environment for the emergence of opportunistic infections, which is concomitant to the increase in antifungal resistance. The use of conventional antifungal drugs as azoles and polyenes can lead to clinical failure, particularly in immunocompromised individuals. Difficulties related to treating fungal infections combined with the time required to develop new drugs, require urgent consideration of other therapeutic alternatives. Drug repurposing is one of the most promising and rapid solutions that the scientific and medical community can turn to, with low costs and safety advantages. To treat life-threatening resistant fungal infections, drug repurposing has led to the consideration of well-known and potential molecules as a last-line therapy. The aim of this review is to provide a summary of current antifungal compounds and their main resistance mechanisms, following by an overview of the antifungal activity of non-traditional antimicrobial drugs. We provide their eventual mechanisms of action and the synergistic combinations that improve the activity of current antifungal treatments. Finally, we discuss drug repurposing for the main emerging multidrug resistant (MDR) fungus, including the Candida auris, Aspergillus or Cryptococcus species.

Ageratum conyzoides L. and Its Secondary Metabolites in the Management of Different Fungal Pathogens

Ageratum conyzoides L. (Family—Asteraceae) is an annual aromatic invasive herb, mainly distributed over the tropical and subtropical regions of the world. It owns a reputed history of indigenous remedial uses, including as a wound dressing, an antimicrobial, and mouthwash as well as in treatment of dysentery, diarrhea, skin diseases, etc. In this review, the core idea is to present the antifungal potential of the selected medicinal plant and its secondary metabolites against different fungal pathogens. Additionally, toxicological studies (safety profile) conducted on the amazing plant A. conyzoides L. are discussed for the possible clinical development of this medicinal herb. Articles available from 2000 to 2020 were reviewed in detail to exhibit recent appraisals of the antifungal properties of A. conyzoides. Efforts were aimed at delivering evidences for the medicinal application of A. conyzoides by using globally recognized scientific search engines and databases so that an efficient approach for filling the lacunae in the research and development of antifungal drugs can be adopted. After analyzing the literature, it can be reported that the selected medicinal plant effectively suppressed the growth of numerous fungal species, such as Aspergillus, Alternaria, Candida, Fusarium, Phytophthora, and Pythium, owing to the presence of various secondary metabolites, particularly chromenes, terpenoids, flavonoids and coumarins. The possible mechanism of action of different secondary metabolites of the plant against fungal pathogens is also discussed briefly. However, it was found that only a few studies have been performed to demonstrate the plant’s dosage and safety profile in humans. Considered all together, A. conyzoides extract and its constituents may act as a promising biosource for the development of effective antifungal formulations for clinical use. However, in order to establish safety and efficacy, additional scientific research is required to explore chronic toxicological effects of ageratum, to determine the probability of interactions when used with different herbs, and to identify safe dosage. The particulars presented here not only bridge this gap but also furnish future research strategies for the investigators in microbiology, ethno-pharmacology, and drug discovery.

Identification and Predictions Regarding the Biosynthesis Pathway of Polyene Macrolides Produced by Streptomyces roseoflavus Men-myco-93-63

A group of polyene macrolides mainly composed of two constituents was isolated from the fermentation broth of Streptomyces roseoflavus Men-myco-93-63, which was isolated from soil where potato scabs were repressed naturally. One of these macrolides was roflamycoin, which was first reported in 1968, and the other was a novel compound named Men-myco-A, which had one methylene unit more than roflamycoin. Together, they were designated RM. This group of antibiotics exhibited broad-spectrum antifungal activities in vitro against 17 plant-pathogenic fungi, with 50% effective concentrations (EC₅₀) of 2.05 to 7.09 μg/ml and 90% effective concentrations (EC₉₀) of 4.32 to 54.45 μg/ml, which indicates their potential use in plant disease control. Furthermore, their biosynthetic gene cluster was identified, and the associated biosynthetic assembly line was proposed based on a module and domain analysis of polyketide synthases (PKSs), supported by findings from gene inactivation experiments.IMPORTANCE Streptomyces roseoflavus Men-myco-93-63 is a biocontrol strain that has been studied in our laboratory for many years and exhibits a good inhibitory effect in many crop diseases. Therefore, the identification of antimicrobial metabolites is necessary and our main objective. In this work, chemical, bioinformatic, and molecular biological methods were combined to identify the structures and biosynthesis of the active metabolites. This work provides a new alternative agent for the biological control of plant diseases and is helpful for improving both the properties and yield of the antibiotics via genetic engineering.

Azole resistance mechanisms in pathogenic M. furfur

Malassezia are emerging fungal pathogens causing opportunistic skin and severe systemic infection. Nosocomial outbreaks are associated with azole resistance and understanding of the underlying mechanisms are limited to knowledge from other fungal species. Herein, we identified distinct antifungal susceptibility patterns in 26 Malassezia furfur isolates derived from healthy and diseased individuals. A Y67F CYP51 mutation was identified in five isolates of M. furfur However, this mutation alone was insufficient to induce reduce azole susceptibility in the wild type strain. RNA-seq and differential gene analysis of healthy and disease derived strains exposed to clotrimazole in vitro identified several key metabolic pathways and transporter proteins which are involved in reduce azole susceptibility. The pleiotropic drug transporter PDR10 was the single most highly upregulated transporter gene in multiple strains of M. furfur after azole treatment and increased expression of PDR10 is associated with reduced azole susceptibility in some systemic disease isolates of M. furfur Deletion of PDR10 in a pathogenic M. furfur strain with reduced susceptibility reduced MIC values to the level of that in susceptible isolates. The current dearth of antifungal technologies, globally emerging multi-azole resistance, and broad agriculture and consumer care use of azoles means improved understanding of the mechanisms underlying intrinsic and acquired azole resistance in Malassezia is crucial for development of antibiotic stewardship and antifungal treatment strategies.

Chemical composition of essential oil and antifungal activity of Artemisia persica Boiss. from Iran

Artemisia is the largest and most diverse genus from the Asteraceae family that named locally "Dermaneh" in Iran. This study was conducted to determine, the chemical compounds of Artemisia persica Boiss essential oil and its antifungal effect, toward six toxigenic fungal strains in vitro. The yield of essential oil from the aerial parts of this plant species, using hydrodistillation method obtained 0.18% (v/w). The results of GC/MS analysis identified 31 components in the essential oil that laciniata furanone E (17.1%), artedouglasia oxide C (13.2%), Trans-pinocarveol (10.2%), pinocarvone (8.5%), and α-pinene (5.8%) were the major compounds. The results of the antifungal activity showed that the most sensitive fungal strains to A. persica Boiss. essential oil were Aspergillus ochraceus and Aspergillus parasiticus with lower minimal fungicidal concentration (MFC) of 1.25 μl/ml (v/v). Also the strong fungicidal effect was observed against Aspergillus flavus and Aspergillus nidulans at a MFC value of 2.5 μl/ml, while the fungicidal activity against Aspergillus fumigatus and Aspergillus niger observed in the 10 μl/ml oil concentration. According to the results A. persica Boiss essential oil has a acceptable antifungal activity against Aspergillus strains and can be used to prevent food crops from fungal contaminations.

Mechanisms of Candida Resistance to Antimycotics and Promising Ways to Overcome It: The Role of Probiotics

Pathogenic Candida and infections caused by those species are now considered as a serious threat to public health. The treatment of candidiasis is significantly complicated by the increasing resistance of pathogenic strains to current treatments and the stagnant development of new antimycotic drugs. Many species, such as Candida auris, have a wide range of resistance mechanisms. Among the currently used synthetic and semi-synthetic antifungal drugs, the most effective are azoles, echinocandins, polyenes, nucleotide analogs, and their combinations. However, the use of probiotic microorganisms and/or the compounds they produce is quite promising, although underestimated by modern pharmacology, to control the spread of pathogenic Candida species.

Inhibitory Effect of Resveratrol on Candida albicans Biofilm Formation

Candida albicans is the primary candidiasis-causing fungal pathogen in humans, and one of its most important virulence factors is the ability to form biofilms. Moreover, these biofilms are often resistant to antifungal agents, so there is a need to develop alternative elimination strategies and therapeutic agents for such infections. The antifungal activity of resveratrol, a phytoalexin polyphenolic compound, impairs the morphological transition of C. albicans under various hypha-inducing conditions and inhibits growth of the yeast-form and mycelia. The purpose of this study was to investigate the effect of resveratrol against C. albicans biofilm formation. The developmental, sustained, and mature stages of biofilm formation were affected or inhibited by resveratrol. Exposure to resveratrol at the developmental stage inhibited growth of C. albicans in a dose-dependent manner. A >30% reduction was observed in sustained biofilm growth in the presence of 200 μg/ml resveratrol in comparison with in its absence. In terms of disruption of matured biofilm, 6.25-100 μg/ml resveratrol significantly reduced cell viability of C. albicans compared with in a control sample (p<0.05). The present results indicate that resveratrol has the potential to serve as an anti-Candida treatment and preventive tool which functions by inhibiting existing or under-forming C. albicans biofilms.

Molecular Markers of Antifungal Resistance: Potential Uses in Routine Practice and Future Perspectives

Antifungal susceptibility testing (AST) has come to establish itself as a mandatory routine in clinical practice. At the same time, the mycological diagnosis seems to have headed in the direction of non-culture-based methodologies. The downside of these developments is that the strains that cause these infections are not able to be studied for their sensitivity to antifungals. Therefore, at present, the mycological diagnosis is correctly based on laboratory evidence, but the antifungal treatment is undergoing a growing tendency to revert back to being empirical, as it was in the last century. One of the explored options to circumvent these problems is to couple non-cultured based diagnostics with molecular-based detection of intrinsically resistant organisms and the identification of molecular mechanisms of resistance (secondary resistance). The aim of this work is to review the available molecular tools for antifungal resistance detection, their limitations, and their advantages. A comprehensive description of commercially available and in-house methods is included. In addition, gaps in the development of these molecular technologies are discussed.

Antifungal Properties of Essential Oils and Their Compounds for Application in Skin Fungal Infections: Conventional and Nonconventional Approaches

Essential oils (EOs) are known to have varying degrees of antimicrobial properties that are mainly due to the presence of bioactive compounds. These include antiviral, nematicidal, antifungal, insecticidal and antioxidant properties. This review highlights the potential of EOs and their compounds for application as antifungal agents for the treatment of skin diseases via conventional and nonconventional approaches. A search was conducted using three databases (Scopus, Web of Science, Google Scholar), and all relevant articles from the period of 2010-2020 that are freely available in English were extracted. In our findings, EOs with a high percentage of monoterpenes showed strong ability as potential antifungal agents. Lavandula sp., Salvia sp., Thymus sp., Citrus sp., and Cymbopogon sp. were among the various species found to show excellent antifungal properties against various skin diseases. Some researchers developed advanced formulations such as gel, semi-solid, and ointment bases to further evaluate the effectiveness of EOs as antifungal agents. To date, most studies on the application of EOs as antifungal agents were performed using in vitro techniques, and only a limited number pursued in vivo and intervention-based research.

Expect the unexpected: fungemia caused by uncommon Candida species in a Turkish University Hospital

Fungemia caused by uncommon Candida species (UCS) (other than C.albicans, C.glabrata, C.parapsilosis, C.tropicalis, C.krusei) is a rare but emerging threat with their potential to exhibit reduced susceptibility or resistance to antifungal agents. We identified 25 patients with UCS fungemia (9 C.kefyr, 8 C.lusitaniae, 4 C.dubliniensis, 2 C.guilliermondii, 1 C.pelliculosa, 1 C.rugosa) through January 2011 and August 2018. Echinocandins were the most common administered agents, followed by fluconazole. Overall mortality was 44%. Echinocandins and voriconazole showed sufficient activity against all tested isolates. High fluconazole MICs among C.guilliermondii, C.pelliculosa, and C.rugosa were determined. MIC value of C.pelliculosa was above the epidemiological cut-off proposed for fluconazole.

Invasive Fungal Infection After Lung Transplantation: Epidemiology in the Setting of Antifungal Prophylaxis

BACKGROUND

Lung transplant recipients commonly develop invasive fungal infections (IFIs), but the most effective strategies to prevent IFIs following lung transplantation are not known.

METHODS

We prospectively collected clinical data on all patients who underwent lung transplantation at a tertiary care academic hospital from January 2007-October 2014. Standard antifungal prophylaxis consisted of aerosolized amphotericin B lipid complex during the transplant hospitalization. For the first 180 days after transplant, we analyzed prevalence rates and timing of IFIs, risk factors for IFIs, and data from IFIs that broke through prophylaxis.

RESULTS

In total, 156 of 815 lung transplant recipients developed IFIs (prevalence rate, 19.1 IFIs per 100 surgeries, 95% confidence interval [CI] 16.4-21.8%). The prevalence rate of invasive candidiasis (IC) was 11.4% (95% CI 9.2-13.6%), and the rate of non-Candida IFIs was 8.8% (95% CI 6.9-10.8%). First episodes of IC occurred a median of 31 days (interquartile range [IQR] 16-56 days) after transplant, while non-Candida IFIs occurred later, at a median of 86 days (IQR 40-121 days) after transplant. Of 169 IFI episodes, 121 (72%) occurred in the absence of recent antifungal prophylaxis; however, IC and non-Candida breakthrough IFIs were observed, most often representing failures of micafungin (n = 16) and aerosolized amphotericin B (n = 24) prophylaxis, respectively.

CONCLUSIONS

Lung transplant recipients at our hospital had high rates of IFIs, despite receiving prophylaxis with aerosolized amphotericin B lipid complex during the transplant hospitalization. These data suggest benefit in providing systemic antifungal prophylaxis targeting Candida for up to 90 days after transplant and extending mold-active prophylaxis for up to 180 days after surgery.

Candida Pathogenicity and Interplay with the Immune System

Candida species are opportunistic fungal pathogens that are part of the normal skin and mucosal microflora. Overgrowth of Candida can cause infections such as thrush or life-threatening invasive candidiasis in immunocompromised patients. Though Candida albicans is highly prevalent, several non-albicans species are also isolated from nosocomial infections. Candida sp. are over presented in the gut of people with Crohn's disease and certain types of neurological disorders, with hyphal form and biofilms being the most virulent states. In addition, Candida uses several secreted and cell surface molecules such as pH related antigen 1, High affinity glucose transporter, Phosphoglycerate mutase 1 and lipases to establish pathogenicity. A strong innate immune response is elicited against Candida via dendritic cells, neutrophils and macrophages. All three complement pathways are also activated. Production of proinflammatory cytokines IL-10 and IL-12 signal differentiation of CD4⁺ cells into Th1 and Th2 cells, whereas IL-6, IL-17 and IL-23 induce Th17 cells. Importance of T-lymphocytes is reflected in depleted T-cell count patients being more prone to Candidiasis. Anti- Candida antibodies also play a role against candidiasis using various mechanisms such as targeting virulent enzymes and exhibiting direct candidacidal activity. However, the significance of antibody response during infection remains controversial. Furthermore, some of the Candida strains have evolved molecular strategies to evade the sophisticated host attack by proteolysis of components of immune system and interfering with immune signalling pathways. Emergence of several non-albicans species that are resistant to current antifungal agents makes treatment more difficult. Therefore, deeper insight into interactions between Candida and the host immune system is required for discovery of novel therapeutic options.

A comparative study on production of extracellular hydrolytic enzymes of Candida species isolated from patients with surgical site infection and from healthy individuals and their co-relation with antifungal drug resistance

BACKGROUND

Surgical site infection (SSI) is a crucial dilemma of surgery. Patients with SSIs not only face difficulty in treatment but also bear extra cost with high mortality rate. Resistant strains of Candida have emerged as an important nosocomial pathogen. Proteinase and phospholipase are exo- enzymes of Candida species, have importance with respect to their contribution in diseases. This study focused on prevalence of Candida species in surgical wound, their resistance to antifungal drugs, co-relation of these resistance with virulence potential of Candida species and comparison of production level of exo-enzymes of Candida species isolated from patients with SSIs and healthy individuals to highlights their role in SSIs.

RESULTS

A total of (n = 555) swab samples were investigated. (n = 450) samples were collected from patients with SSIs and (n = 105) were collected from healthy individuals. Samples were subjected for the identification of Candida species which were subsequently investigated for antifungal susceptibility, MICs and enzymatic activity of Candida species. Out of 128 strains of Candida spp. isolated from SSIs, 54(42.18%) were identified as C. albicans followed by C. glabrata 32(25%), C. parapsilosis 17(13.28%), C. krusei 13(10.16%) and C. tropicalis 12(9.38%). C. albicans isolates showed 100% susceptibility to voriconazole and amphotericin B followed by itraconazole 98% and fluconazole 89%. Out of 6 fluconazole resistant C. albicans 5(83.33%) were able to produce phospholipase while out of 48 fluconazole-susceptible strains 17(35.42%) were found to be phospholipase producer. Out of 54 C. albicans isolated from surgical wound 46(85.18%) and 49(90.74%) were found to be phospholipase and proteinase producer respectively, whereas out of 20 C. albicans isolates from healthy subjects 14(70%) produce proteinase and 12(60%) produce phospholipase. There were significant statistical differences found between the level of enzyme production by C. albicans, in relation to both sites (P = 0.014).

CONCLUSION

Study revealed that prevalence of Candida species is high in SSIs. Phospholipase and proteinase activity were more pronounced in Candida Species from surgical wound in contrast to species from healthy individuals suggests these enzymes may have been responsible for the severity of infection in surgical wound patients.

Preclinical Evaluation of Acylhydrazone SB-AF-1002 as a Novel Broad-Spectrum Antifungal Agent

The incidence of invasive fungal infections is rising due to the increase in susceptible populations. Current clinically available drugs have therapeutic limitations due to toxicity, a narrow spectrum of activity, and, more importantly, the consistent rise of fungal species that are intrinsically resistant or that develop resistance due to prolonged therapy. Thus, there is an urgent need for new broad-spectrum antifungal agents with low toxicity and a novel mechanism of action. We previously reported a new class of potent antifungal compounds, acylhydrazones, that target the fungal sphingolipid pathway. Based upon our initial lead molecules, (E)-N'-(5-bromo-2-hydroxybenzylidene)-2-methylbenzohydrazide and D13, we performed a structure-activity relationship study, synthesizing ca. 300 new compounds. Of these, 5 compounds were identified to be the most promising for further studies, based on their broad-spectrum activity and low toxicity in mammalian cells lines. Among these top 5 lead compounds, we report here the impressive in vivo activity of 2,4-dibromo-N'-(5-bromo-2-hydroxybenzylidene)benzohydrazide (SB-AF-1002) in several models of systemic fungal infection. Our data show that SB-AF-1002 is efficacious and outperforms current standard-of-care drugs in models of invasive fungal infections, such as cryptococcosis, candidiasis, and aspergillosis. Specifically, animals treated with SB-AF-1002 not only survived the infection but also showed a clearing of fungal cells from key organs. Moreover, SB-AF-1002 was very effective in an aspergillosis model as a prophylactic therapy. SB-AF-1002 also displayed acceptable pharmacokinetic properties in mice, similar to those of the parent compound, D13. These results clearly indicate that our novel acylhydrazones constitute a new class of highly potent and efficacious antifungal agents which warrant further development for the treatment of invasive fungal infections.

In vitro and ex vivo biofilms of dermatophytes: a new panorama for the study of antifungal drugs

This study describes an ex vivo model that creates an environment for dermatophyte biofilm growth, with features that resemble those of in vivo conditions, designing a new panorama for the study of antifungal susceptibility. Regarding planktonic susceptibility, MIC ranges were 0.125-1 µg ml^-1 for griseofulvin and 0.000097-0.25 µg ml^-1 for itraconazole and terbinafine. sMIC50 ranges were 2->512 µg ml^-1 for griseofulvin and 0.25->64 µg ml^-1 for itraconazole and terbinafine. CLSM images demonstrated a reduction in the amount of cells within the biofilm, but hyphae and conidia were still observed and biofilm biomass was maintained. SEM analysis demonstrated a retraction in the biofilm matrix, but fungal structures and water channels were preserved. These results show that ex vivo biofilms are more tolerant to antifungal drugs than in vitro biofilms, suggesting that environmental and nutritional conditions created by this ex vivo model favor biofilm growth and robustness, and hence drug tolerance.

Antifungal Resistance Regarding Malassezia pachydermatis: Where Are We Now?

Malassezia pachydermatis is a yeast inhabiting the skin and ear canals in healthy dogs. In the presence of various predisposing conditions it can cause otitis and dermatitis, which are treated with multiple antifungal agents, mainly azole derivatives. This manuscript aims to review the available evidence regarding the occurrence of resistance phenomena in this organism. Various findings support the capacity of M. pachydermatis for developing resistance. These include some reports of treatment failure in dogs, the reduced antifungal activity found against yeast isolates sampled from dogs with exposure to antifungal drugs and strains exposed to antifungal agents in vitro, and the description of resistance mechanisms. At the same time, the data reviewed may suggest that the development of resistance is a rare eventuality in canine practice. For example, only three publications describe confirmed cases of treatment failure due to antifungal resistance, and most claims of resistance made by past studies are based on interpretive breakpoints that lack sound support from the clinical perspective. However, it is possible that resistant cases are underreported in literature, perhaps due to the difficulty of obtaining a laboratory confirmation given that a standard procedure for susceptibility testing of M. pachydermatis is still unavailable. These considerations highlight the need for maintaining surveillance for the possible emergence of clinically relevant resistance, hopefully through a shared strategy put in place by the scientific community.

Antifungal Activity of Capric Acid, Nystatin, and Fluconazole and Their In Vitro Interactions Against Candida Isolates from Neonatal Oral Thrush

Due to the increasing resistance of various Candida species to azole drugs, particularly fluconazole, it would be of significant importance to look for alternative therapies. The aim of this study was to investigate the antifungal activity of capric acid and its in vitro interactions with nystatin and fluconazole against Candida isolates. A total of 40 Candida isolates (C. albicans, 36; C. kefyr, 2; C. tropicalis, 1; C. glabrata, 1) collected from the oral cavity of neonates with oropharyngeal candidiasis and a reference strain of C. albicans (ATCC 10231) were used in this study. Antifungal activity of capric acid and two comparator antifungal drugs, namely fluconazole and nystatin, was tested according to CLSI M27-A3/M60 method. The in vitro interaction between capric acid with fluconazole and nystatin was determined following a checkerboard method and results were interpreted using fractional inhibitory concentration index. Nystatin had the lowest minimum inhibitory concentrations (range, 0.125-8 μg/mL; geometric mean [GM], 0.6229 μg/mL) followed by fluconazole (range, 0.5-16 μg/mL; GM, 1.9011 μg/mL) and capric acid (range, 128-2,048 μg/mL; GM, 835.9756 μg/mL). When tested in combination, capric acid with fluconazole demonstrated synergistic, indifferent, and antagonistic interactions in 3 (7.317%), 24 (58.536%), and 14 (34.146%) cases, respectively. For combination of capric acid with nystatin, synergistic, indifferent, and antagonistic interactions were observed in 1 (2.439%), 19 (46.341%), and 21 (51.219%) cases, respectively. All cases of synergistic interactions were against resistant or susceptible dose-dependent isolates. Fluconazole, nystatin, and capric acid seem to be more effective when they are used alone compared with their combination. However, their combination might be effective on resistant isolates.

Mecanismos de resistencia a fluconazol expresados por Candida glabrata: una situación para considerar en la terapéutica

Introducción: Los esfuerzos terapéuticos orientados a atender las micosis por Candida spp. se han enfocado en el empleo de azoles; sin embargo, en la literatura científica se discute su beneficio, por los amplios y descritos mecanismos de resistencia. Objetivo: Describir los mecanismos de resistencia al fluconazol expresados por la especie Candida glabrata, con la intención de que sean considerados dentro de las variables de elegibilidad para la intervención. Método: Se realizó una revisión integrativa utilizando la pregunta orientadora: ¿cuáles son los mecanismos de resistencia al fluconazol expresados por la especie Candida glabrata? Veintinueve estudios obtenidos de la base de datos PubMed cumplieron los criterios del análisis crítico propuesto por el instrumento PRISMA, utilizado para la selección de los artículos incluidos para su revisión en este manuscrito. Las categorías bajo las cuales se organizaron los elementos de análisis fueron: sobrexpresión de bombas de eflujo y modificaciones en la enzima lanosterol 14-alfa-desmetilasa. Resultados: Los mecanismos de resistencia al fluconazol expresados por Candida glabrata están determinados principalmente por la regulación a la alza de bombas de adenosina-trifosfato Binding Cassette (ABC) y por la modificación del punto de unión con su blanco farmacológico: la enzima lanosterol 14-alfa-desmetilasa. Conclusión: Los mecanismos de resistencia expresados por Candida glabrata se asocian con la modificación estructural de la diana farmacológica y la sobreexpresión de bombas de eflujo de manera diferencial a otras especies. Se sugiere que Candida glabrata es intrínsecamente menos susceptible al fluconazol.

Antimicrobial Metal Nanomaterials: From Passive to Stimuli-Activated Applications

The development of antimicrobial drug resistance among pathogenic bacteria and fungi is one of the most significant health issues of the 21st century. Recently, advances in nanotechnology have led to the development of nanomaterials, particularly metals that exhibit antimicrobial properties. These metal nanomaterials have emerged as promising alternatives to traditional antimicrobial therapies. In this review, a broad overview of metal nanomaterials, their synthesis, properties, and interactions with pathogenic micro-organisms is first provided. Secondly, the range of nanomaterials that demonstrate passive antimicrobial properties are outlined and in-depth analysis and comparison of stimuli-responsive antimicrobial nanomaterials are provided, which represent the next generation of microbiocidal nanomaterials. The stimulus applied to activate such nanomaterials includes light (including photocatalytic and photothermal) and magnetic fields, which can induce magnetic hyperthermia and kinetically driven magnetic activation. Broadly, this review aims to summarize the currently available research and provide future scope for the development of metal nanomaterial-based antimicrobial technologies, particularly those that can be activated through externally applied stimuli.

The yeast, the antifungal, and the wardrobe: a journey into antifungal resistance mechanisms of Candida tropicalis

Candida tropicalis is a prominent non-Candida albicans Candida species involved in cases of candidemia, mainly causing infections in patients in intensive care units and (or) those presenting neutropenia. In recent years, several studies have reported an increase in the recovery rates of azole-resistant C. tropicalis isolates. Understanding C. tropicalis resistance is of great importance, since resistant strains are implicated in persistent or recurrent and breakthrough infections. In this review, we address the main mechanisms underlying C. tropicalis resistance to the major antifungal classes used to treat candidiasis. The main genetic basis involved in C. tropicalis antifungal resistance is discussed. A better understanding of the epidemiology of resistant strains and the mechanisms involved in C. tropicalis resistance can help improve diagnosis and assessment of the antifungal susceptibility of this Candida species to improve clinical management.

Prevalence and Therapeutic Challenges of Fungal Drug Resistance: Role for Plants in Drug Discovery

Antimicrobial resistance is a global issue that threatens the effective practice of modern medicine and global health. The emergence of multidrug-resistant (MDR) fungal strains of Candida auris and azole-resistant Aspergillus fumigatus were highlighted in the Centers for Disease Control and Prevention’s (CDC) 2019 report, Antibiotic Resistance Threats in the United States. Conventional antifungals used to treat fungal infections are no longer as effective, leading to increased mortality. Compounding this issue, there are very few new antifungals currently in development. Plants from traditional medicine represent one possible research path to addressing the issue of MDR fungal pathogens. In this commentary piece, we discuss how medical ethnobotany—the study of how people use plants in medicine—can be used as a guide to identify plant species for the discovery and development of novel antifungal therapies.

Análisis cuantitativo de la expresión de genes de resistencia a fluconazol en cepas de Candida albicans aisladas al ingreso de adultos mayores a una unidad de cuidados intensivos de Manizales, Colombia

Introducción.

Las infecciones oportunistas asociadas con Candida albicans han tenido gran repercusión en la salud pública por la mortalidad que generan en determinados grupos poblacionales. Aunque existen tratamientos farmacológicos disponibles, es evidente el aumento de la resistencia desarrollada por el agente patógeno, por lo que la determinación de los mecanismos de resistencia de las cepas presentes en las áreas hospitalarias es importante, ya que permitiría plantear mejores esquemas de tratamiento.

Objetivo.

Analizar la expresión de los genes ERG11, CDR1 y MDR1 en cepas de C. albicans aisladas de adultos mayores a su ingreso en la unidad de cuidados intensivos del Hospital Santa Sofía de Manizales, Colombia.

Materiales y métodos.

Se seleccionaron 29 muestras (21 resistentes y 8 sensibles) y se conformaron dos grupos de trabajo, uno de muestras con exposición al fluconazol y el otro sin esta. El ARN extraído se cuantificó mediante reacción en cadena de la polimerasa con transcriptasa inversa en tiempo real (RT-qPCR).

Resultados.

Se encontraron diferencias significativas en la expresión del gen MDR1 en el grupo de cepas de C. albicans resistentes. Dos de las cepas resistentes (104 y 62-2) expuestas al antifúngico presentaron valores muy elevados en la expresión de este gen. La expresión del ERG11 y del CDR1 no fue significativa en los grupos estudiados.

Conclusión.

El aumento de sobreexpresión del gen MDR1 indica que este puede ser el responsable de la resistencia; sin embargo, algunas cepas resistentes no sobreexpresaron los genes analizados, lo que indica que puede haber otros genes involucrados en la resistencia de las cepas estudiadas.

Elevated minimum inhibitory concentrations to antifungal drugs prevail in 14 rare species of candidemia-causing Saccharomycotina yeasts

Antifungal susceptibility profiles of rare Saccharomycotina yeasts remain missing, even though an increase in prevalence of such rare Candida species was reported in candidemia. Majority of these rare yeast species carry intrinsic resistances against at least one antifungal compound. Some species are known to be cross-resistant (against multiple drugs of the same drug class) or even multi-drug resistant (against multiple drugs of different drug classes). We performed antifungal susceptibility testing (AFST) according to EUCAST broth microdilution for 14 rare species (Clavispora lusitaniae, Candida intermedia, Candida auris, Diutina rugosa, Wickerhamiella pararugosa, Yarrowia lipolytica, Pichia norvegensis, Candida nivariensis, Kluyveromyces marxianus, Wickerhamomyces anomalus, Candida palmioleophila, Meyerozyma guilliermondii, Meyerozyma caribbica, and Debaryomyces hansenii) known to cause candidemia. In total, 234 isolates were tested for amphotericin B, fluconazole, itraconazole, voriconazole, posaconazole, anidulafungin, micafungin, and caspofungin. Amphothericin B had the broadest efficiency against the 14 tested rare yeast species, while high minimum inhibitory concentrations (MICs) against azole drugs and echinocandins were common. Voriconazole was the most efficient azole drug. Multidrug resistance was observed for the species C. auris and K. marxianus. Multidrug resistant individual isolates were found for Y. lipolytica and M. caribbica. In conclusion, the observed high MIC values of the rare Saccharomycotina species tested limit antifungal treatment options, complicating the management of such infections.

Chemical diversity and mode of action of natural products targeting lipids in the eukaryotic cell membrane

Covering: up to 2019Nature furnishes bioactive compounds (natural products) with complex chemical structures, yet with simple, sophisticated molecular mechanisms. When natural products exhibit their activities in cells or bodies, they first have to bind or react with a target molecule in/on the cell. The cell membrane is a major target for bioactive compounds. Recently, our understanding of the molecular mechanism of interactions between natural products and membrane lipids progressed with the aid of newly-developed analytical methods. New technology reconnects old compounds with membrane lipids, while new membrane-targeting molecules are being discovered through the screening for antimicrobial potential of natural products. This review article focuses on natural products that bind to eukaryotic membrane lipids, and includes clinically important molecules and key research tools. The chemical diversity of membrane-targeting natural products and the molecular basis of lipid recognition are described. The history of how their mechanism was unveiled, and how these natural products are used in research are also mentioned.

Virulence and biofilms as promising targets in developing antipathogenic drugs against candidiasis

Candida albicans has remained the main etiological agent of candidiasis, challenges clinicians with high mortality and morbidity. The emergence of resistance to antifungal drugs, toxicity and lower efficacy have all contributed to an urgent need to develop alternative drugs aiming at novel targets in C. albicans. Targeting the production of virulence factors, which are essential processes for infectious agents, represents an attractive substitute for the development of newer anti-infectives. The present review highlights the recent developments made in the understanding of the pathogenicity of C. albicans. Production of hydrolytic enzymes, morphogenesis and biofilm formation, along with their molecular and metabolic regulation in Candida are discussed with regard to the development of novel antipathogenic drugs against candidiasis.

Over the last decade, candidiasis has remained a major problematic disease worldwide. In spite of the existence of many antifungal drugs, the treatment of such diseases has still remained unsuccessful due to drug inefficacy. Therefore, there is a need to discover antifungals with different modes of action, such as antipathogenic drugs against Candida albicans. Here, we describe how various types of virulence factors such as proteinase, phospholipase, hemolysin, adhesion, morphogenesis and biofilm formation, could be targeted to develop novel therapeutics. We can inhibit production of these virulence factors by controlling their molecular/metabolic regulation.

Candida albicans Antifungal Resistance and Tolerance in Bloodstream Infections: The Triad Yeast-Host-Antifungal

Candida albicans represents the most frequent isolated yeast from bloodstream infections. Despite the remarkable progress in diagnostic and therapeutic approaches, these infections continue to be a critical challenge in intensive care units worldwide. The economic cost of bloodstream fungal infections and its associated mortality, especially in debilitated patients, remains unacceptably high. Candida albicans is a highly adaptable microorganism, being able to develop resistance following prolonged exposure to antifungals. Formation of biofilms, which diminish the accessibility of the antifungal, selection of spontaneous mutations that increase expression or decreased susceptibility of the target, altered chromosome abnormalities, overexpression of multidrug efflux pumps and the ability to escape host immune defenses are some of the factors that can contribute to antifungal tolerance and resistance. The knowledge of the antifungal resistance mechanisms can allow the design of alternative therapeutically options in order to modulate or revert the resistance. We have focused this review on the main factors that are involved in antifungal resistance and tolerance in patients with C. albicans bloodstream infections.

Genome-wide screening and in silico gene knockout to predict potential candidates for drug designing against Candida albicans

C. albicans infections are increasingly becoming a threat to public health with emergence of drug resistant strains. It emphasizes the need to look for alternate drug targets through genome-wide screening. In the present study, whole proteome of C. albicans SC5314 was analyzed in single click target mining workflow of TiDv2. A protein-protein interaction network (PPI) for the resulting putative targets was generated based on String database. Ninety four proteins with higher connectivity (degree ≥ 10) in the network are noted as hub genes. Among them, 24 are observed to be known targets while 70 are novel ones. Further, chokepoint analysis revealed FAS2, FOL1 and ERG5 as chokepoint enzymes in their respective pathways. Subsequently, the chokepoints were selected as prior interest for in silico gene knockout via MATLAB and COBRA Toolbox. In silico gene knockout pointed that FAS2 inhibition reduced the growth rate of pathogen from 0.2879 mmol.gDW^-1.h^-1 to zero. Furthermore, enzyme inhibition assay of FAS2 with cerulenin strengthen the computational outcome with MIC 1.25 μg/mL. Hence, the study establishes FAS2 as a promising target to design therapeutics against C. albicans.

Oxadiazolylthiazoles as novel and selective antifungal agents

Studying the structure-activity relationships (SAR) of oxadiazolylthiazole antibiotics unexpectedly led us to identify ethylenediamine- and propylenediamine-analogs as potential antimycotic novel lead structures. Replacement of the ethylenediamine moiety for the lead compound 7 with cis-diaminocyclohexyl group (compound 18) significantly enhanced the antifungal activity. In addition to the high safety margin of 18 against mammalian cells, it showed highly selective broad-spectrum activity against fungal cells without inhibiting the human normal microbiota. The antifungal activity of 18 was investigated against 20 drug-resistant clinically important fungi, including Candida species, Cryptococcus, and Aspergillus fumigatus strains. In addition to the low MIC values that mostly ranged between 0.125 and 2.0 μg/mL, compound 18 outperformed fluconazole in disrupting mature Candida biofilm.

Blue light therapy to treat candida vaginitis with comparisons of three wavelengths: an in vitro study

Anti-fungal blue light (ABL) therapies have been widely studied to treat various microbial infections in the literature. The blue light with wavelengths ranging from 400 to 470 nm has been reported to be effective to inhibit various kinds of bacteria and fungi. The existing studies usually report the viability rates of the pathogens under the irradiation of the blue light with different dosage parameters. However, to the best of our knowledge, there is still no work especially focusing on studying the effect of ABL therapies on treating candida vaginitis, where it is important to study the viability of both the Candida albicans (C. albicans) and the human vaginal epithelial cells. It is the purpose of this work to conduct ABL experiments on both of these two cells, analyze the effects, and determine the best ABL wavelength out of three candidates, i.e., 405-nm, 415-nm, and 450-nm wavelength. The viability rates of the C. albicans and the human vaginal epithelial cells irradiated by the three blue LED light sources were measured, whose irradiance (power density) were all set to 50 mW/cm². The dynamic viability models of the C. albicans and the epithelial cells were built based on the experimental data. Moreover, in this work, we also built a functional relationship between the viability of these two types of cells, by which we further compared the effects of the blue light irradiation on both the C. albicans and vaginal epithelial cells. The experimental data showed that when an approximately 80% inhibiting rate of the C. albicans was achieved, the survival rates of the epithelial cells were 0.6700, 0.7748, and 0.6027, respectively for the treatment by the 405-nm, 415-nm, and 450-nm wavelength light. On the other hand, by simulating the functional relationship between the viability of the two types of cells, the survival rates of the epithelial cells became 0.5783, 0.6898, and 0.1918 respectively using the 405-nm, 415-nm and 450-nm wavelength light, when the C. albicans was completely inhibited. Therefore, both the experimental data and the model simulation results have demonstrated that the 415-nm light has a more effective anti-fungal result with less damage to the epithelial cells than the 405-nm and 450-nm light.

In vitro activity of four triazole antifungal drugs against clinically common and uncommon yeast species

Background and Purpose:

Incidence of fungal infections caused by opportunistic fungal pathogens, such as yeasts and yeast-like species, has undergone an increase in otherwise healthy individuals. These pathogens account for high mortality and show reduced susceptibility to the routine antifungal drugs. Accordingly, antifungal susceptibility testing is an urgent need in the determination of the susceptibility spectrum of antifungals and selection of appropriate antifungal agents for the management of patients with fungal infection.

Materials and Methods:

The present study was conducted on 110 yeast strains belonging to 15 species recovered from clinical specimens. Susceptibility of the isolates to four antifungal drugs (i.e., fluconazole, itraconazole, voriconazole, and posaconazole) was tested according to the Clinical and Laboratory Standards Institute guidelines M27-A3 and M27-S4.

Results:

Fluconazole exhibited no activity against 4.3% (n=2) of C. albicans isolates, whereas the remaining 44 isolates had a minimum inhibitory concentration (MIC) range of 0.125-4 μg/ml. Voriconazole had the lowest geometric mean MIC (0.03 µg/ml) against all isolated yeast species, followed by posaconazole (0.07 µg/ml), itraconazole (0.10 µg/ml), and fluconazole (0.60 µg/ml). Overall, all of the isolates had reduced voriconazole MICs with a MIC range of 0.016-0.5 μg/ml, except for one isolate of C. albicans that had a MIC of 1 μg/ml. Candida haemulonii as a multidrug-resistant fungus showed a fluconazole MIC of > 64 μg/ml.

Conclusion:

The current study provides insight into the antifungal susceptibility profiles of clinically common and uncommon yeast species to four triazole antifungal agents. According to our findings, voriconazole was the most active agent. Awareness about antifungal susceptibility patterns is highly helpful in the selection of appropriate antifungal drugs and identification of the efficiency of the currently used agents.

Quinine Improves the Fungicidal Effects of Antimicrobial Blue Light: Implications for the Treatment of Cutaneous Candidiasis

BACKGROUND AND OBJECTIVE

Candida albicans is an opportunistic fungal pathogen of clinical importance and is the primary cause of fungal-associated wound infections, sepsis, or pneumonia in immunocompromised individuals. With the rise in antimicrobial resistance, it is becoming increasingly difficult to successfully treat fungal infections using traditional antifungals, signifying that alternative non-traditional approaches must be explored for their efficacy.

STUDY DESIGN/MATERIALS AND METHODS

We investigated the combination of antimicrobial blue light (aBL) and quinine hydrochloride (Q-HCL) for improved inactivation of C. albicans, in vitro and in vivo, relative to either monotherapy. In addition, we evaluated the safety of this combination therapy in vivo using the TUNEL assay.

RESULTS

The combination of aBL (108 J/cm² ) with Q-HCL (1 mg/mL) resulted in a significant improvement in the inactivation of C. albicans planktonic cells in vitro, where a 7.04 log₁₀ colony forming units (CFU) reduction was achieved, compared with aBL alone that only inactivated 3.06 log₁₀ CFU (P < 0.001) or Q-HCL alone which did not result in a loss of viability. aBL + Q-HCL was also effective at inactivating 48-hour biofilms, with an inactivation 1.73 log₁₀ CFU at the dose of 108 J/cm² aBL and 1 mg/mL Q-HCL, compared with only a 0.73 or 0.66 log₁₀ CFU by aBL and Q-HCL alone, respectively (P < 0.001). Transmission electron microscopy revealed that aBL + Q-HCL induced morphological and ultrastructural changes consistent with cell wall and cytoplasmic damage. In addition, aBL + Q-HCL was effective at eliminating C. albicans within mouse abrasion wounds, with a 2.47 log₁₀ relative luminescence unit (RLU) reduction at the dose of 324 J/cm² aBL and 0.4 mg/cm² Q-HCL, compared with a 1.44 log₁₀ RLU reduction by aBL alone. Q-HCL or nystatin alone did not significantly reduce the RLU. The TUNEL assay revealed some apoptotic cells before and 24 hours following treatment with aBL + Q-HCL.

CONCLUSION

The combination of aBL + Q-HCL was effective at eliminating C. albicans both in vitro and in vivo. A comprehensive assessment of toxicity (cytotoxicity and genotoxicity) is required to fully determine the safety of aBL + Q-HCL therapy at different doses. In conclusion, the combination of aBL and Q-HCL may be a viable option for the treatment of cutaneous candidiasis. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Electrochemical Strategy for Eradicating Fluconazole-Tolerant Candida albicans Using Implantable Titanium

A persistent problem in modern health care derives from the overwhelming presence of antibiotic-resistant microbes on biomaterials, more specifically, fungal growth on metal-based implants. This study seeks to investigate the antifungal properties of low-level electrochemical treatments delivered using titanium electrodes against Candida albicans. We show that C. albicans can be readily controlled with electrical currents/potentials, reducing the number of viable planktonic cells by 99.7% and biofilm cells by 96.0-99.99%. Additionally, this study explores the ability of the electrochemical treatments to potentiate fluconazole, a clinically used antifungal drug. We have found that electrochemical treatment substantially enhances fluconazole killing activity. While fluconazole alone exhibits a low efficiency against the stationary phase and biofilm cells of C. albicans, complete eradication corresponding to 7-log killing is achieved when the antifungal drug is provided subsequently to the electrochemical treatment. Further mechanistic analyses have revealed that the sequential treatment shows a complex multimodal action, including the disruption of cell wall integrity and permeability, impaired metabolic functions, and enhanced susceptibility to fluconazole, while altering the biofilm structure. Altogether, we have developed and optimized a new therapeutic strategy to sensitize and facilitate the eradication of fluconazole-tolerant microbes from implantable materials. This work is expected to help advance the use of electrochemical approaches in the treatment of infections caused by C. albicans in both nosocomial and clinical cases.

Anticandidal agent for multiple targets: the next paradigm in the discovery of proficient therapeutics/overcoming drug resistance

Candida albicans is a prominent human fungal pathogen. Current treatments are suffering a massive gap due to emerging resistance against available antifungals. Therefore, there is an ardent need for novel antifungal candidates that essentially have more than one target, as most antifungal repertoires are single-target drugs. Exploration of multiple-drug targeting in antifungal therapeutics is still pending. An extensive literature survey was performed to categorize and comprehend relevant studies and the current therapeutic scenario that led researchers to preferentially consider multitarget drug-based Candida infection therapy. With this article, we identified and compiled a few potent antifungal compounds that are directed toward multiple virulent targets in C. albicans. Such compound(s) provide an optimistic platform of multiple targeting and could leave a substantial impact on the development of effective antifungals.

Prospective CYP2C19-Guided Voriconazole Prophylaxis in Patients With Neutropenic Acute Myeloid Leukemia Reduces the Incidence of Subtherapeutic Antifungal Plasma Concentrations

A risk mitigation strategy was implemented to determine if a higher prophylactic voriconazole dosage in patients with CYP2C19 rapid metabolizer neutropenic acute myeloid leukemia (AML) reduces the incidence of subtherapeutic trough concentrations. Patients with AML (n = 263) were preemptively genotyped for CYP2C19*2, *3, and *17 alleles as part of a single-center prospective, interventional, quality improvement study. CYP2C19 rapid metabolizers (CYP2C19*1/*17) were recommended to receive interventional voriconazole 300 mg twice daily, ultrarapid metabolizers (CYP2C19*17/*17) were recommended to avoid voriconazole, and all others received the standard prophylactic dosage of 200 mg twice daily. In this real-world setting, 202 patients (76.8%) were prescribed prophylactic voriconazole, and of these patients 176 (87.1%) received CYP2C19-guided prophylactic dosing. Voriconazole trough concentrations were obtained for 41 of the 58 (70.7%) CYP2C19 rapid metabolizers prescribed prophylactic voriconazole. Interventional voriconazole resulted in higher plasma trough concentrations (median 2.7 μg/mL) compared with the standard prophylactic dosage (median 0.6 μg/mL; P = 0.001). Subtherapeutic concentrations were avoided in 83.8% of CYP2C19 rapid metabolizers receiving interventional dosage compared to 46.2% receiving standard dosage (P = 0.02). CYP2C19 genotyping to preemptively guide prophylactic voriconazole dosing is feasible and may be a potential strategy for reducing the risk of subtherapeutic trough concentrations that potentiate breakthrough fungal infections.