Development of a Luminex-based multiplex assay for detection of mutations conferring resistance to Echinocandins in Candida glabrata

High-Throughput Monitoring of Pathogenic Fungal Growth Using Whole Slide Imaging for Rapid Antifungal Susceptibility Assessment

Invasive fungal infections are a major health threat with high morbidity and mortality, highlighting the urgent need for rapid diagnostic tools to detect antifungal resistance. Traditional culture-based antifungal susceptibility testing (AFST) methods often fall short due to their lengthy process. In our previous research, we developed a whole-slide imaging (WSI) technique for the high-throughput assessment of bacterial antibiotic resistance. Building on this foundation, this study expands the application of WSI by adapting it for rapid AFST through high-throughput monitoring of the growth of hundreds of individual fungi. Due to the distinct "budding" growth patterns of fungi, we developed a unique approach that utilizes specific cell number change to determine fungi replication, instead of cell area change used for bacteria in our previous study, to accurately determine the growth rates of individual fungal cells. This method not only accelerates the determination of antifungal resistance by directly observing individual fungal cell growth, but also yields accurate results. Employing Candida albicans as a representative model organism, reliable minimum inhibitory concentration (MIC) of fluconazole inhibiting 100% cells of Candida albicans (denoted as MIC100) was obtained within 3h using the developed method, while the modified broth dilution method required 72h for the similar reliable result. In addition, our approach was effectively utilized to test blood culture samples directly, eliminating the need to separate the fungi from whole blood samples spiked with Candida albicans. These features indicate the developed method holds great potential serving as a general tool in rapid antifungal susceptibility testing and MIC determination.

Molecular Mechanisms Associated with Antifungal Resistance in Pathogenic Candida Species

Candidiasis is a highly pervasive infection posing major health risks, especially for immunocompromised populations. Pathogenic Candida species have evolved intrinsic and acquired resistance to a variety of antifungal medications. The primary goal of this literature review is to summarize the molecular mechanisms associated with antifungal resistance in Candida species. Resistance can be conferred via gain-of-function mutations in target pathway genes or their transcriptional regulators. Therefore, an overview of the known gene mutations is presented for the following antifungals: azoles (fluconazole, voriconazole, posaconazole and itraconazole), echinocandins (caspofungin, anidulafungin and micafungin), polyenes (amphotericin B and nystatin) and 5-fluorocytosine (5-FC). The following mutation hot spots were identified: (1) ergosterol biosynthesis pathway mutations (ERG11 and UPC2), resulting in azole resistance; (2) overexpression of the efflux pumps, promoting azole resistance (transcription factor genes: tac1 and mrr1; transporter genes: CDR1, CDR2, MDR1, PDR16 and SNQ2); (3) cell wall biosynthesis mutations (FKS1, FKS2 and PDR1), conferring resistance to echinocandins; (4) mutations of nucleic acid synthesis/repair genes (FCY1, FCY2 and FUR1), resulting in 5-FC resistance; and (5) biofilm production, promoting general antifungal resistance. This review also provides a summary of standardized inhibitory breakpoints obtained from international guidelines for prominent Candida species. Notably, N. glabrata, P. kudriavzevii and C. auris demonstrate fluconazole resistance.

Rapid Antifungal Susceptibility Testing Based on Single-Cell Metabolism Analysis Using Stimulated Raman Scattering Imaging

Rapid antifungal susceptibility testing (AFST) is urgently needed in clinics to treat invasive fungal infections with the appropriate antifungal drugs and to slow the emergence of antifungal resistance. However, current AFST methods are time-consuming (24-48 h) due to the slow growth of fungal cells and the methods not being able to work directly for clinical samples. Here, we demonstrate rapid AFST by measuring the metabolism in single fungal cells using stimulated Raman scattering imaging and deuterium probing. Distinct metabolic responses were observed in Candida albicans to different classes of antifungal drugs: while the metabolism was inhibited by amphotericin B, it was stimulated by azoles (fluconazole and voriconazole) and micafungin. Accordingly, we propose metabolism change as a biomarker for rapid AFST. The results were obtained in 4 h with 100% categorical agreement with the gold standard broth microdilution test. In addition, a protocol was developed for direct AFST from positive blood cultures. This method overcomes the limitation of slow growth in conventional methods and has the potential for the rapid diagnosis of candidemia and other clinical fungal infections.

Tackling the emerging threat of antifungal resistance to human health

Invasive fungal infections pose an important threat to public health and are an under-recognized component of antimicrobial resistance, an emerging crisis worldwide. Across a period of profound global environmental change and expanding at-risk populations, human-infecting pathogenic fungi are evolving resistance to all licensed systemic antifungal drugs. In this Review, we highlight the main mechanisms of antifungal resistance and explore the similarities and differences between bacterial and fungal resistance to antimicrobial control. We discuss the research and innovation topics that are needed for risk reduction strategies aimed at minimizing the emergence of resistance in pathogenic fungi. These topics include links between the environment and One Health, surveillance, diagnostics, routes of transmission, novel therapeutics and methods to mitigate hotspots for fungal adaptation. We emphasize the global efforts required to steward our existing antifungal armamentarium, and to direct the research and development of future therapies and interventions.

Antifungal Susceptibility Testing: A Primer for Clinicians

Clinicians treating patients with fungal infections may turn to susceptibility testing to obtain information regarding the activity of different antifungals against a specific fungus that has been cultured. These results may then be used to make decisions regarding a patient's therapy. However, for many fungal species that are capable of causing invasive infections, clinical breakpoints have not been established. Thus, interpretations of susceptible or resistant cannot be provided by clinical laboratories, and this is especially true for many molds capable of causing severe mycoses. The purpose of this review is to provide an overview of susceptibility testing for clinicians, including the methods used to perform these assays, their limitations, how clinical breakpoints are established, and how the results may be put into context in the absence of interpretive criteria. Examples of when susceptibility testing is not warranted are also provided.

Paving the Way to Overcome Antifungal Drug Resistance: Current Practices and Novel Developments for Rapid and Reliable Antifungal Susceptibility Testing

The past year has established the link between the COVID-19 pandemic and the global spread of severe fungal infections; thus, underscoring the critical need for rapid and realizable fungal disease diagnostics. While in recent years, health authorities, such as the Centers for Disease Control and Prevention, have reported the alarming emergence and spread of drug-resistant pathogenic fungi and warned against the devastating consequences, progress in the diagnosis and treatment of fungal infections is limited. Early diagnosis and patient-tailored therapy are established to be key in reducing morbidity and mortality associated with fungal (and cofungal) infections. As such, antifungal susceptibility testing (AFST) is crucial in revealing susceptibility or resistance of these pathogens and initiating correct antifungal therapy. Today, gold standard AFST methods require several days for completion, and thus this much delayed time for answer limits their clinical application. This review focuses on the advancements made in developing novel AFST techniques and discusses their implications in the context of the practiced clinical workflow. The aim of this work is to highlight the advantages and drawbacks of currently available methods and identify the main gaps hindering their progress toward clinical application.

Can We Improve Antifungal Susceptibility Testing?

Systemic antifungal agents are increasingly used for prevention or treatment of invasive fungal infections, whose prognosis remains poor. At the same time, emergence of resistant or even multi-resistant strains is of concern as the antifungal arsenal is limited. Antifungal susceptibility testing (AFST) is therefore of key importance for patient management and antifungal stewardship. Current AFST methods, including reference and commercial types, are based on growth inhibition in the presence of an antifungal, in liquid or solid media. They usually enable Minimal Inhibitory Concentrations (MIC) to be determined with direct clinical application. However, they are limited by a high turnaround time (TAT). Several innovative methods are currently under development to improve AFST. Techniques based on MALDI-TOF are promising with short TAT, but still need extensive clinical validation. Flow cytometry and computed imaging techniques detecting cellular responses to antifungal stress other than growth inhibition are also of interest. Finally, molecular detection of mutations associated with antifungal resistance is an intriguing alternative to standard AFST, already used in routine microbiology labs for detection of azole resistance in Aspergillus and even directly from samples. It is still restricted to known mutations. The development of Next Generation Sequencing (NGS) and whole-genome approaches may overcome this limitation in the near future. While promising approaches are under development, they are not perfect and the ideal AFST technique (user-friendly, reproducible, low-cost, fast and accurate) still needs to be set up routinely in clinical laboratories.

Emergence of resistant Candida glabrata in Germany

Background

Candida glabrata is the second leading fungal pathogen causing candidaemia and invasive candidiasis in Europe. This yeast is recognized for its rapid ability to acquire antifungal drug resistance.

Objectives

We systematically evaluated 176 C. glabrata isolates submitted to the German National Reference Center for Invasive Fungal Infections (NRZMyk) between 2015 and 2019 with regard to echinocandin and fluconazole susceptibility.

Methods

Susceptibility testing was performed using a reference protocol (EUCAST) and a range of commercial assays. Hot spot regions of the echinocandin target FKS genes were sequenced using Sanger sequencing.

Results

In total, 84 of 176 isolates were initially classified as anidulafungin-resistant based on EUCAST testing. Of those, 71 harboured mutations in the glucan synthase encoding FKS genes (13% in FKS1, 87% in FKS2). Significant differences in anidulafungin MICs were found between distinct mutation sites. 11 FKS wild-type (WT) isolates initially classified as resistant exhibited anidulafungin MICs fluctuating around the interpretation breakpoint upon re-testing with multiple assays. Two FKS WT isolates consistently showed high anidulafungin MICs and thus must be considered resistant despite the absence of target gene mutations. Over one-third of echinocandin-resistant strains displayed concomitant fluconazole resistance. Of those, isolates linked to bloodstream infection carrying a change at Ser-663 were associated with adverse clinical outcome.

Conclusions

Resistant C. glabrata strains are emerging in Germany. Phenotypic echinocandin testing can result in misclassification of susceptible strains. FKS genotyping aids in detecting these strains, however, echinocandin resistance may occur despite a wild-type FKS genotype.

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.

Evaluation of Surveyor nuclease for rapid identification of FKS genes mutations in Candida glabrata

INTRODUCTION

Infections with Candida glabrata have recently gained worldwide attention owing to its association with long hospitalizations and high mortality rates. This problem is highlighted when the infection is associated with echinocandin resistance, which is used for first-line therapy. Echinocandin resistance is exclusively attributed to functional mutations in FKS genes, and especially in hot spot (HS) regions. Unfortunately, few studies have focused on the rapid identification of FKS mutations associated with echinocandin resistance in C. glabrata. This study was intended to evaluate and validate the use of Surveyor nuclease assay (SN) for detection of FKS gene mutations.

METHODS

SN was evaluated against three segments of FKS1 and FKS2 genes including whole gene, regions including all HSs, and the region including only HS1.

RESULTS

Our results showed that SN results are basically dependent on the type of gene as well as the segment type. Interestingly, SN can detect mutations in the region containing HS1 in both FKS1 and FKS2 genes. Furthermore, SN can detect mutations in the segment containing all HS regions for FKS1 but not FKS2. SN was unable to detect mutations in the whole FKS1 and FKS2 genes.

CONCLUSIONS

As far as we know, this is the first study to validate SN for rapid identification of FKS gene mutations. This assay could be used as a sample for rapid identification of mutations associated with HS1 region in FKS genes, which have a predominant role for echinocandin resistance induction in C. glabrata.

Molecular Diagnosis of Yeast Infections

PURPOSE OF REVIEW

The use of molecular tests to aid the diagnosis of invasive yeast infection, in particular invasive candidosis, has been described for over two decades, yet widespread application is limited, and diagnosis remains heavily dependent on classical microbiology. This article will review developments from the past decade in attempt to build on existing knowledge. It will highlight clinical performance and limitations while reviewing developments on recognized procedures; it will also provide insight into novel approaches incorporated in response to clinical demand (e.g. C. auris and antifungal resistance) or technological advances (e.g. next-generation sequencing).

RECENT FINDINGS

Limited methodological standardization and, until recently, unavailability of commercial options have hindered the integration of molecular diagnostics for yeasts. The development of certain, novel commercial methods has received considerable evaluation allowing a greater understanding of individual assay performance, but widespread multicentre evaluation of most commercial kits is lacking. The detection of emerging pathogens (e.g. C. auris) has been enhanced by the development of molecular tests. Molecular methods are providing a better understanding of the mycobiome, mechanisms of resistance and epidemiology/phylogeny.

SUMMARY

Despite over two decades of use, the incorporation of molecular methods to enhance the diagnosis of yeast infections remains limited to certain specialist centres. While the development of commercial tests will provide stimulus for broader application, further validation and reduced costs are required. Over the same period of time, Aspergillus PCR has become more widely accepted driven by international efforts to standardize methodology; it is critical that yeast PCR follows suit. Next-generation sequencing will provide significant information on the mycobiome, antifungal resistance mechanism and even broad-range detection directly from the specimen, which may be critical for the molecular detection of yeasts other than Candida species, which is currently limited.

Antifungal Resistance in Candida auris: Molecular Determinants

Since Candida auris integrates strains resistant to multiple antifungals, research has been conducted focused on knowing which molecular mechanisms are involved. This review aims to summarize the results obtained in some of these studies. A search was carried out by consulting websites and online databases. The analysis indicates that most C. auris strains show higher resistance to fluconazole, followed by amphotericin B, and less resistance to 5-fluorocytosine and caspofungin. In C. auris, antifungal resistance to amphotericin B has been linked to an overexpression of several mutated ERG genes that lead to reduced ergosterol levels; fluconazole resistance is mostly explained by mutations identified in the ERG11 gene, as well as a higher number of copies of this gene and the overexpression of efflux pumps. For 5-fluorocytosine, it is hypothesized that the resistance is due to mutations in the FCY2, FCY1, and FUR1 genes. Resistance to caspofungin has been associated with a mutation in the FKS1 gene. Finally, resistance to each antifungal is closely related to the type of clade to which the strain belongs.

Antifungal Susceptibility Testing: Current Approaches

Although not as ubiquitous as antibacterial susceptibility testing, antifungal susceptibility testing (AFST) is a tool of increasing importance in clinical microbiology laboratories. The goal of AFST is to reliably produce MIC values that may be used to guide patient therapy, inform epidemiological studies, and track rates of antifungal drug resistance. There are three methods that have been standardized by standards development organizations: broth dilution, disk diffusion, and azole agar screening for Aspergillus Other commonly used methods include gradient diffusion and the use of rapid automated instruments. Novel methodologies for susceptibility testing are in development. It is important for laboratories to consider not only the method of testing but also the interpretation (or lack thereof) of in vitro data.

Echinocandin resistance among Candida isolates at an academic medical centre 2005-15: analysis of trends and outcomes

Objectives

To identify the frequency of micafungin resistance among clinically significant isolates of Candida stored at our institution from 2005 to 2015. Chart review of patients with resistant isolates then informed the clinical setting and outcomes associated with these infections.

Methods

Clinical Candida isolates had been stored at -80°C in Brucella broth with 20% glycerol from 2005. Isolates were tested using broth microdilution to determine micafungin MICs. All Candida glabrata isolates and all isolates demonstrating decreased susceptibility to micafungin were screened for FKS mutations using a Luminex assay.

Results

In total, 3876 Candida isolates were tested for micafungin resistance, including 832 C. glabrata isolates. Of those, 33 isolates from 31 patients were found to have either decreased susceptibility to micafungin and/or an FKS mutation. C. glabrata accounted for the majority of these isolates. While bloodstream infections were found to have a very high mortality rate, isolates from other sites were uncommonly associated with 30-day mortality. Overall resistance rates were very low.

Conclusions

Echinocandin resistance in C. glabrata has been increasingly reported but rates at our institution remain very low. We hypothesize that a focus on antifungal stewardship may have led to these observations. Knowledge of local resistance patterns is key to appropriate empirical treatment strategies.

Recent trends in molecular diagnostics of yeast infections: from PCR to NGS

The incidence of opportunistic yeast infections in humans has been increasing over recent years. These infections are difficult to treat and diagnose, in part due to the large number and broad diversity of species that can underlie the infection. In addition, resistance to one or several antifungal drugs in infecting strains is increasingly being reported, severely limiting therapeutic options and showcasing the need for rapid detection of the infecting agent and its drug susceptibility profile. Current methods for species and resistance identification lack satisfactory sensitivity and specificity, and often require prior culturing of the infecting agent, which delays diagnosis. Recently developed high-throughput technologies such as next generation sequencing or proteomics are opening completely new avenues for more sensitive, accurate and fast diagnosis of yeast pathogens. These approaches are the focus of intensive research, but translation into the clinics requires overcoming important challenges. In this review, we provide an overview of existing and recently emerged approaches that can be used in the identification of yeast pathogens and their drug resistance profiles. Throughout the text we highlight the advantages and disadvantages of each methodology and discuss the most promising developments in their path from bench to bedside.

Anidulafungin Susceptibility Testing of Candida glabrata Isolates from Blood Cultures by the MALDI Biotyper Antibiotic (Antifungal) Susceptibility Test Rapid Assay

Echinocandins are the recommended first-line antifungals for treatment of invasive candidiasis. The increasing number of Candida glabrata strains resistant against echinocandins is an emerging health care concern. The rapid detection of resistant C. glabrata isolates is an urgent requirement for clinical laboratories. In this study, we developed the MALDI Biotyper antibiotic (antifungal) susceptibility test rapid assay (MBT ASTRA) for the rapid detection of anidulafungin-resistant C. glabrata isolates directly from positive blood cultures. Of 100 C. glabrata strains, MBT ASTRA classified 69 as susceptible and 29 as resistant. Microdilution assays performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines, used as a standard reference, identified 65 susceptible, 9 intermediate, and 26 resistant isolates. Sequencing of hot spot 1 and hot spot 2 regions of the FKS1 and FKS2 genes classified 86 susceptible and 14 resistant isolates. The MBT ASTRA had sensitivity and specificity of 80% and 95%, respectively, compared to the microdilution method. Positive and negative agreement of MBT ASTRA was calculated at 100% and 80%, respectively, compared with the molecular sequencing approach. Together, these results revealed a high accuracy of MBT ASTRA compared to microdilution according to the CLSI and PCR analysis, resulting in a categorical agreement of 90% and 83%, respectively. The validity of MBT ASTRA was 98%. Importantly, MBT ASTRA provided antifungal susceptibility testing (AFST) within 6 h that was both accurate and reliable compared to the other two approaches, which require at least 24 h or are costly. Therefore, this method has the potential to facilitate clinical AFST rapidly at low sample costs for clinical labs already equipped with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).

Drug susceptibility profile of Candida glabrata clinical isolates from Iran and genetic resistant mechanisms to caspofungin

BACKGROUND

Candida glabrata is a yeast that can cause hazardous fungal infections with high mortality and drug resistance.

AIMS

The aim of this study was to determine the profile of drug susceptibility in clinical isolates of C. glabrata and review the resistance mechanisms to caspofungin.

METHODS

A total of 50 C. glabrata clinical isolates from Iran were tested for in vitro susceptibilities to amphotericin B, caspofungin, fluconazole and voriconazole. To investigate the mechanism of resistance to caspofungin, hotspot areas of FKS1 and FKS2 genes were sequenced and gene expression profile was evaluated.

RESULTS

All the isolates were susceptible to amphotericin B and caspofungin. Fluconazole resistance was exhibited in four isolates. In addition, only one isolate was resistant to voriconazole. FKS2 with 12 point mutations showed more mutations compared to FKS1 that had only two mutations. All substitutions were synonymous. FKS genes were expressed at comparable levels (no statistical significance) in caspofungin-treated and non-treated cultures.

CONCLUSIONS

The silent mutations in the hotspot areas of FKS genes and inconsiderable changes in gene expression were not associated with increased MIC (0.25μg/ml). Other mechanisms of resistance which include mutations outside the hotspot area of FKS genes could be involved in a slight increase of MIC, and they should be identified through complete FKS gene sequencing.

Emerging multidrug-resistant Candida species

PURPOSE OF REVIEW

To describe the epidemiology, strategies for early detection, and clinical management of infections caused by the most commonly found multidrug-resistant (MDR) Candida spp.

RECENT FINDINGS

Increasing numbers of reports describing invasive infections by MDR Candida auris and Candida glabrata has been reported in medical centers worldwide.

SUMMARY

We checked all papers published along the last 10 years describing epidemiological, diagnostic, and clinical aspects of infections by MDR Candida spp., with emphasis on C. auris and C. glabrata spp. C. auris has been reported in 15 countries and multidrug resistance rates is usually above 30%. Horizontal transmission is a great concern regarding C. auris. C. glabrata ranks the second most reported Candida spp. in deep-seated infections from United States and some European Centers, although multidrug resistance rates above 10% are restricted to some US centers. Candida haemulonii complex isolates with poor susceptibility to azoles and amphotericin B have been isolated in superficial and deep-seated infections, whereas Candida guilliiermondii complex isolates with poor susceptibility to azoles and echinocandins have been recovered from catheter-related bloodstream infections. Other potential MDR Candida species are Candida krusei, Candida lusitaniae, Candida kefyr, Yarrowia (Candida) lypolitica, and Candida rugosa.

Culture-Independent Molecular Methods for Detection of Antifungal Resistance Mechanisms and Fungal Identification

Resistance to azoles and echinocandins has emerged as a significant factor affecting the clinical management of patients with invasive fungal infections. Immunosuppressed patients at high risk for invasive fungal infections often have prolonged or repeated exposure to antifungals resulting in either the well-documented selection of naturally occurring, less susceptible fungal species, or the in situ development of specific resistance mechanisms. Nucleic acid-based molecular diagnostics are particularly well suited for the rapid detection of low-abundance fungal pathogens and identification of the infecting pathogen to the genus and species levels, as well as assessment of resistance mechanisms. A wide range of molecular probing technologies involving real-time polymerase chain reaction (PCR) assays that facilitate direct analysis of a single infecting genome in a sterile blood specimen are available and have recently been commercialized (eg, Roche LightCycler SeptiFast and T2 Biosystems T2Candida). One of the exciting applications of molecular technology is the direct detection of specific resistance mechanisms that evolve during therapy. In principle, the detection of resistance mechanisms that have been independently validated to cause resistance provides a culture-independent biomarker for potential therapeutic failure. The emergence of real-time PCR assays utilizing allele-specific molecular detection technology that is highly sensitive, robust, and high-throughput has the potential to improve patient care by providing faster detection of drug-resistant infecting strains and to help inform therapeutic management.

Yeasts

Yeasts are unicellular organisms that reproduce mostly by budding and less often by fission. Most medically important yeasts originate from Ascomycota or Basidiomycota. Here, we review taxonomy, epidemiology, disease spectrum, antifungal drug susceptibility patterns of medically important yeast, laboratory diagnosis, and diagnostic strategies.

New approaches for antifungal susceptibility testing

BACKGROUND

Invasive fungal diseases, including those caused by (multi)drug-resistant Candida and Aspergillus species, still represent global public health concerns. Information about the antifungal susceptibility testing (AFST) of fungal isolates must be quickly produced to help clinicians in administrating appropriate antifungal therapies. Unfortunately, reference AFST methods, albeit accurate, are labour-intensive and take several hours before patients' results can be available to the treating clinicians.

AIMS AND SOURCES

This review is a blend of evidence obtained from PubMed literature searches, clinical laboratory experience and the author's opinions that is aimed to summarize recent significant advances and ongoing challenges in the AFST area.

CONTENT

Particular attention is given to the new approaches based on genetic or phenotypic recognition of antifungal resistance that are destined to enhance the clinical usefulness of AFST in the near future. Following short-term exposures of fungal cells to antifungal drugs, new antifungal susceptibility end-points have been established, and novel diagnostic assay platforms have been proposed for the genotyping assessment of fungal isolates with resistance-associated mutations. Overall, new approaches provide a rapid, reliable means of identifying those fungal isolates with phenotypically detectable acquired resistance mechanisms, independently from the clinical susceptibility categorization of the isolates as obtained in a classical AFST way.

IMPLICATIONS

Despite holding promise as a surrogate diagnostic method to better direct antifungal therapy, the AFST approaches described in this review need to be evaluated in multicentre laboratory studies to enable their standardization and refinement.

Antifungal Therapy: New Advances in the Understanding and Treatment of Mycosis

The high rates of morbidity and mortality caused by fungal infections are associated with the current limited antifungal arsenal and the high toxicity of the compounds. Additionally, identifying novel drug targets is challenging because there are many similarities between fungal and human cells. The most common antifungal targets include fungal RNA synthesis and cell wall and membrane components, though new antifungal targets are being investigated. Nonetheless, fungi have developed resistance mechanisms, such as overexpression of efflux pump proteins and biofilm formation, emphasizing the importance of understanding these mechanisms. To address these problems, different approaches to preventing and treating fungal diseases are described in this review, with a focus on the resistance mechanisms of fungi, with the goal of developing efficient strategies to overcoming and preventing resistance as well as new advances in antifungal therapy. Due to the limited antifungal arsenal, researchers have sought to improve treatment via different approaches, and the synergistic effect obtained by the combination of antifungals contributes to reducing toxicity and could be an alternative for treatment. Another important issue is the development of new formulations for antifungal agents, and interest in nanoparticles as new types of carriers of antifungal drugs has increased. In addition, modifications to the chemical structures of traditional antifungals have improved their activity and pharmacokinetic parameters. Moreover, a different approach to preventing and treating fungal diseases is immunotherapy, which involves different mechanisms, such as vaccines, activation of the immune response and inducing the production of host antimicrobial molecules. Finally, the use of a mini-host has been encouraging for in vivo testing because these animal models demonstrate a good correlation with the mammalian model; they also increase the speediness of as well as facilitate the preliminary testing of new antifungal agents. In general, many years are required from discovery of a new antifungal to clinical use. However, the development of new antifungal strategies will reduce the therapeutic time and/or increase the quality of life of patients.

Rapid Detection of FKS-Associated Echinocandin Resistance in Candida glabrata

A novel and highly accurate diagnostic assay platform was established for rapid identification of FKS mutations associated with echinocandin resistance in Candida glabrata The assay platform uses allele-specific molecular beacon and DNA melt analysis following asymmetric PCR. A dual assay for FKS1 and FKS2 was developed to identify within 3 h the most common and clinically relevant resistance-associated mutations, including 8 FKS1 HS1 (wild type [WT], S629P, F625S, D632Y, D632E [T1896G], D632E [T1896A], I634V, and F625F) and 7 FKS2 HS1 (WT, F659del, F659S, F659V, F659L, S663P, and S663F) genotypes. A blinded panel of 188 C. glabrata clinical isolates was tested by both assays. The molecular diagnostic results from the dual assay were 100% concordant with data obtained from DNA sequencing. This platform has the potential to overcome the deficiencies of existing in vitro susceptibility-based assays to identify echinocandin-resistant C. glabrata and holds promise as a surrogate diagnostic method to better direct echinocandin therapy.

Clinical perspectives on echinocandin resistance among Candida species

PURPOSE OF REVIEW

We review and offer our clinical perspectives on the emergence of echinocandin-resistant Candida.

RECENT FINDINGS

Candida FKS gene mutations attenuate echinocandin activity, but overall mutation rates among clinical isolates remain low (Candida glabrata, ∼4%; other species, <1%). Rates are higher with prior echinocandin exposure, exceeding 50% among C. glabrata or Candida albicans isolates causing breakthrough invasive candidiasis. The median duration of prior echinocandin exposure among FKS mutant isolates is ∼100 days. The clinical usefulness of echinocandin susceptibility testing is limited by the low overall prevalence of resistance, and uncertainties surrounding testing methods and interpretation of minimum inhibitory concentrations (MICs). In single-center studies, caspofungin resistance (defined using institution-specific MIC breakpoints) was 32-53% sensitive and 75-95% specific for predicting treatment outcomes of C. glabrata invasive candidiasis; corresponding values for the presence of an FKS mutation were 35-41% and 90-98%. Results were similar using anidulafungin and micafungin MICs. Clinical data are scarce for non-C. glabrata species.

SUMMARY

Echinocandins remain preferred agents against invasive Candida infections. Susceptibility testing and FKS genotypic testing do not have roles in routine clinical practice, but may be useful in newly-diagnosed patients who are echinocandin-experienced or those who have not responded to echinocandin treatment.

Update from the Laboratory: Clinical Identification and Susceptibility Testing of Fungi and Trends in Antifungal Resistance

Despite the availability of new diagnostic assays and broad-spectrum antifungal agents, invasive fungal infections remain a significant challenge to clinicians and are associated with marked morbidity and mortality. In addition, the number of etiologic agents of invasive mycoses has increased accompanied by an expansion in the immunocompromised patient populations, and the use of molecular tools for fungal identification and characterization has resulted in the discovery of several cryptic species. This article reviews various methods used to identify fungi and perform antifungal susceptibility testing in the clinical laboratory. Recent developments in antifungal resistance are also discussed.

Epidemiology and Risk Factors for Echinocandin Nonsusceptible Candida glabrata Bloodstream Infections: Data From a Large Multisite Population-Based Candidemia Surveillance Program, 2008-2014

Background. Echinocandins are first-line treatment for Candida glabrata candidemia. Echinocandin resistance is concerning due to limited remaining treatment options. We used data from a multisite, population-based surveillance program to describe the epidemiology and risk factors for echinocandin nonsusceptible (NS) C glabrata candidemia.

Methods. The Centers for Disease Control and Prevention's Emerging Infections Program conducts population-based laboratory surveillance for candidemia in 4 metropolitan areas (7.9 million persons; 80 hospitals). We identified C glabrata cases occurring during 2008–2014; medical records of cases were reviewed, and C glabrata isolates underwent broth microdilution antifungal susceptibility testing. We defined echinocandin-NS C glabrata (intermediate or resistant) based on 2012 Clinical and Laboratory Standards Institute minimum inhibitory concentration breakpoints. Independent risk factors for NS C glabrata were determined by stepwise logistic regression.

Results. Of 1385 C glabrata cases, 83 (6.0%) had NS isolates (19 intermediate and 64 resistant); the proportion of NS isolates rose from 4.2% in 2008 to 7.8% in 2014 (P < .001). The proportion of NS isolates at each hospital ranged from 0% to 25.8%; 3 large, academic hospitals accounted for almost half of all NS isolates. In multivariate analysis, prior echinocandin exposure (adjusted odds ratio [aOR], 5.3; 95% CI, 2.6–1.2), previous candidemia episode (aOR, 2.5; 95% CI, 1.2–5.1), hospitalization in the last 90 days (aOR, 1.9; 95% CI, 1.0–3.5, and fluconazole resistance [aOR, 3.6; 95% CI, 2.0–6.4]) were significantly associated with NS C glabrata. Fifty-nine percent of NS C glabrata cases had no known prior echinocandin exposure.

Conclusion. The proportion of NS C glabrata isolates rose significantly during 2008–2014, and NS C glabrata frequency differed across hospitals. In addition to acquired resistance resulting from prior drug exposure, occurrence of NS C glabrata without prior echinocandin exposure suggests possible transmission of resistant organisms.

Molecular diagnostic methods for invasive fungal disease: the horizon draws nearer?

Rapid, accurate diagnostic laboratory tests are needed to improve clinical outcomes of invasive fungal disease (IFD). Traditional direct microscopy, culture and histological techniques constitute the 'gold standard' against which newer tests are judged. Molecular diagnostic methods, whether broad-range or fungal-specific, have great potential to enhance sensitivity and speed of IFD diagnosis, but have varying specificities. The use of PCR-based assays, DNA sequencing, and other molecular methods including those incorporating proteomic approaches such as matrix-assisted laser desorption ionisation-time of flight mass spectroscopy (MALDI-TOF MS) have shown promising results. These are used mainly to complement conventional methods since they require standardisation before widespread implementation can be recommended. None are incorporated into diagnostic criteria for defining IFD. Commercial assays may assist standardisation. This review provides an update of molecular-based diagnostic approaches applicable to biological specimens and fungal cultures in microbiology laboratories. We focus on the most common pathogens, Candida and Aspergillus, and the mucormycetes. The position of molecular-based approaches in the detection of azole and echinocandin antifungal resistance is also discussed.

Development of a Multilocus Sequence Typing System for Medically Relevant Bipolaris Species

Multilocus sequence typing (MLST) is the gold standard genotyping technique for many microorganisms. This classification approach satisfies the requirements for a high-resolution, standardized, and archivable taxonomic system. Here, we describe the development of a novel MLST system to assist with the investigation of an unusual cluster of surgical site infections caused by Bipolaris spp. in postoperative cardiothoracic surgery (POCS) patients during January 2008 to December 2013 in the southeastern United States. We also used the same MLST system to perform a retrospective analysis on isolates from a 2012 Bipolaris endophthalmitis outbreak caused by a contaminated product. This MLST system showed high intraspecies discriminatory power for Bipolaris spicifera, B. hawaiiensis, and B. australiensis. Based on the relatedness of the isolates, the MLST data supported the hypothesis that infections in the POCS cluster were from different environmental sources while confirming that the endophthalmitis outbreak resulted from a point source, which was a contaminated medication.

Echinocandin resistance: an emerging clinical problem?

PURPOSE OF REVIEW

Echinocandin resistance in Candida is a great concern, as the echinocandin drugs are recommended as first-line therapy for patients with invasive candidiasis. Here, we review recent advances in our understanding of the epidemiology, underlying mechanisms, methods for detection and clinical implications.

RECENT FINDINGS

Echinocandin resistance has emerged over the recent years. It has been found in most clinically relevant Candida spp., but is most common in C. glabrata with rates exceeding 10% at selected institutions. It is most commonly detected after 3-4 weeks of treatment and is associated with a dismal outcome. An extensive list of mutations in hot spot regions of the genes encoding the target has been characterized and associated with species and drug-specific loss of susceptibility. The updated antifungal susceptibility testing reference methods identify echinocandin-resistant isolates reliably, although the performance of commercial tests is somewhat more variable. Alternative technologies are being developed, including molecular detection and matrix-assisted laser desorption ionization-time of flight.

SUMMARY

Echinocandin resistance is increasingly encountered and its occurrence makes susceptibility testing essential, particularly in patients with prior exposure. The further development of rapid and user-friendly commercially available susceptibility platforms is warranted. Antifungal stewardship is important in order to minimize unnecessary selection pressure.

Emerging issues with diagnosis and management of fungal infections in solid organ transplant recipients

Invasive fungal infections (IFIs) are being increasingly recognized in solid organ transplant (SOT) recipients, and delayed diagnosis can lead to graft loss and death. Therefore, there is a low threshold for prophylaxis and early initiation of empiric antifungal treatment, in this patient population. Meanwhile, the increasing consumption of antifungals is associated with high cost, medication toxicities and the emergence of resistance in Candida species, all of which call for rational use of antifungal agents. The implementation of fungal biomarkers, molecular diagnostic methods and direct detection of volatile fungal metabolites in breath samples could lead to faster diagnosis, early appropriate treatment and improved clinical outcomes, but also aid in the de-escalation of antifungal treatment. Those novel diagnostic modalities need to be validated specifically in SOT recipients. Infectious diseases consultation can contribute to optimization of care through prompt initiation and appropriate modification of antifungal treatment, management of medication toxicities and drug-drug interactions, as well as source control. In this review, we conceptually summarize recent advances in the diagnosis and management of IFI in SOT recipients, and highlight the importance of early diagnostic tools and good stewardship of antifungal drugs.

Declining incidence of candidemia and the shifting epidemiology of Candida resistance in two US metropolitan areas, 2008-2013: results from population-based surveillance

Background

Recent reports have demonstrated a decline in bacterial bloodstream infections (BSIs) following adherence to central line insertion practices; however, declines have been less evident for BSIs due to Candida species.

Methods

We conducted active, population-based laboratory surveillance for candidemia in metropolitan Atlanta, GA and Baltimore, MD over a 5-year period. We calculated annual candidemia incidence and antifungal drug resistance rates.

Results

We identified 3,848 candidemia cases from 2008–2013. Compared with 2008, candidemia incidence per 100,000 person-years decreased significantly by 2013 in both locations (GA: 14.1 to 9.5, p<0.001; MD: 30.9 to 14.4, p<0.001). A total of 3,255 cases (85%) had a central venous catheter (CVC) in place within 2 days before the BSI culture date. In both locations, the number of CVC-associated cases declined (GA: 473 to 294; MD: 384 to 151). Candida albicans (CA, 36%) and Candida glabrata (CG, 27%) were the most common species recovered. In both locations, the proportion of cases with fluconazole resistance decreased (GA: 8.0% to 7.1%, −10%; MD: 6.6% to 4.9%, −25%), while the proportion of cases with an isolate resistant to an echinocandin increased (GA: 1.2% to 2.9%, +147%; MD: 2.0% to 3.5%, +77%). Most (74%) echinocandin-resistant isolates were CG; 17 (<1%) isolates were resistant to both drug categories (multidrug resistant [MDR], 16/17 were CG). The proportion of CG cases with MDR Candida increased from 1.8% to 2.6%.

Conclusions

We observed a significant decline in the incidence of candidemia over a five-year period, and increases in echinocandin-resistant and MDR Candida. Efforts to strengthen infection control practices may be preventing candidemia among high-risk patients. Further surveillance for resistant Candida is warranted.

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.

Set of classical PCRs for detection of mutations in Candida glabrata FKS genes linked with echinocandin resistance

Clinical echinocandin resistance among Candida glabrata strains is increasing, especially in the United States. Antifungal susceptibility testing is considered mandatory to guide therapeutic decisions. However, these methodologies are not routinely performed in the hospital setting due to their complexity and the time needed to obtain reliable results. Echinocandin failure in C. glabrata is linked exclusively to Fks1p and Fks2p amino acid substitutions, and detection of such substitutions would serve as a surrogate marker to identify resistant isolates. In this work, we report an inexpensive, simple, and quick classical PCR set able to objectively detect the most common mechanisms of echinocandin resistance in C. glabrata within 4 h. The usefulness of this assay was assessed using a blind collection of 50 C. glabrata strains, including 16 FKS1 and/or FKS2 mutants.

Role of FKS Mutations in Candida glabrata: MIC values, echinocandin resistance, and multidrug resistance

Candida glabrata is the second leading cause of candidemia in U.S. hospitals. Current guidelines suggest that an echinocandin be used as the primary therapy for the treatment of C. glabrata disease due to the high rate of resistance to fluconazole. Recent case reports indicate that C. glabrata resistance to echinocandins may be increasing. We performed susceptibility testing on 1,380 isolates of C. glabrata collected between 2008 and 2013 from four U.S. cities, Atlanta, Baltimore, Knoxville, and Portland. Our analysis showed that 3.1%, 3.3%, and 3.6% of the isolates were resistant to anidulafungin, caspofungin, and micafungin, respectively. We screened 1,032 of these isolates, including all 77 that had either a resistant or intermediate MIC value with respect to at least one echinocandin, for mutations in the hot spot regions of FKS1 and FKS2, the major mechanism of echinocandin resistance. Fifty-one isolates were identified with hot spot mutations, 16 in FKS1 and 35 in FKS2. All of the isolates with an FKS mutation except one were resistant to at least one echinocandin by susceptibility testing. Of the isolates resistant to at least one echinocandin, 36% were also resistant to fluconazole. Echinocandin resistance among U.S. C. glabrata isolates is a concern, especially in light of the fact that one-third of those isolates may be multidrug resistant. Further monitoring of U.S. C. glabrata isolates for echinocandin resistance is warranted.