Notable Increasing Trend in Azole Non-susceptible Candida tropicalis Causing Invasive Candidiasis in China (August 2009 to July 2014): Molecular Epidemiology and Clinical Azole Consumption

Candidaemia: A 9-Year Retrospective Analysis of Epidemiology and Antimicrobial Susceptibility in Tertiary Care Hospitals in Western China

Purpose

This investigation endeavors to scrutinize the resistance profiles to antifungal agents, alongside the clinical distribution of Candida isolates that yielded positive results in blood cultures at Suining Central Hospital spanning the years 2015 to 2023. The objective is to provide crucial epidemiological insights that may aid in early clinical intervention and judicious deployment of antifungal therapies.

Methods

This retrospective analysis analyses data on 182 different Candida strains with positive clinical blood cultures obtained from the Microbiology Laboratory of Suining Central Hospital over a period of nine consecutive years. The study involved identification of Candida species and assessment of resistance patterns to fungal drugs.

Results

Our analysis revealed that the median age of patients diagnosed with Candidaemia from the 182 strains was 62 years, with a distribution of 63.7% females and 36.3% males. Within the cohort of 182 Candida strains, Candida albicans constituted 32.4%, while non-albicans Candida species comprised 67.6% of the cases. Specifically, Candida tropicalis represented 37.4%, Candida glabrata 12.1%, Candida parapsilosis 11.0%,Candida guilliermondii 3.8%, and both Candida krusei and Candida Dublin accounted for 1.6% each. These Candida species were predominantly identified in intensive care units (ICU), hematology, gastroenterology, neurology centers, and endocrine metabolism units.

Conclusion

The findings of this investigation suggest a shift in the prevalence of non-Candida albicans species, notably C. tropicalis, as the predominant cause of Candidaemia at Suining Central Hospital, surpassing C. albicans. Although instances of antifungal resistance are infrequent, there has been a notable rise in resistance to azoles. This study provides important insights into the local epidemiology, which will be essential for informing the selection of empirical antifungal therapy and contributing to the global surveillance of antifungal resistance.

Epidemiology of Invasive Candidiasis

Invasive candidiasis (IC) is an increasingly prevalent, costly, and potentially fatal infection brought on by the opportunistic yeast, Candida. Previously, IC has predominantly been caused by C. albicans which is often drug susceptible. There has been a global trend towards decreasing rates of infection secondary to C. albicans and a rise in non-albicans species with a corresponding increase in drug resistance creating treatment challenges. With advances in management of malignancies, there has also been an increase in the population at risk from IC along with a corresponding increase in incidence of breakthrough IC infections. Additionally, the emergence of C. auris creates many challenges in management and prevention due to drug resistance and the organism's ability to transmit rapidly in the healthcare setting. While the development of novel antifungals is encouraging for future management, understanding the changing epidemiology of IC is a vital step in future management and prevention.

Epidemiology and Risk Factors of Candidemia a 8-Year Retrospective Study from a Teaching Hospital in China

Purpose

We investigated the Epidemiology, risk factors and outcomes of Candida bloodstream infection.

Methods

The electronic laboratory records data of patients with candidemia (2015-2022) were collected. We used univariate and multivariate logistic regression to determine the risk factors of candidemia.

Results

Of the 134 patients with candidemia, the most prevalent species were Candida albicans (37.2%), followed by Candida glabrata (27.7%), Candida parapsilosis (18.9%), and others. The mean annual incidence was 0.33/1000 admissions. The overall resistance rate of Candida spp. against fluconazole and voriconazole were 4.9% (7/142) and 5.9% (6/101), while Candida tropicalis showed high resistance to fluconazole (38.8%) and voriconazole (27.8%). The 30-day mortality rate was 32.8%. On multivariate analysis, age ≥ 65 (odds ratio [OR] = 3.874, 95% confidence interval [CI]: 1.146, 13.092; P = 0.029), high Acute Physiology and Chronic Health Evaluation II (APACHE II) score (OR = 12.384, 95% CI: 2.963, 51.762; P = 0.001), shock (OR = 3.428, 95% CI: 1.097, 10.719; P = 0.034), initial antifungal therapy (OR = 0.057, 95% CI: 0.011, 0.306; P = 0.001) and White blood cells (OR = 1.129, 95% CI: 1.016, 1.255; P = 0.024) were the independent risk factors with mortality within 30 day in patients with candidemia.

Conclusion

The incidence rate and the mortality rate of candidemia are high, and lower azole susceptibility was found in Candida tropicalis. Age≥65 years, Shock, high APACHE II score, Antifungal therapy and White blood cells count were independently associated with 30-day mortality.

The Impact of the Fungal Priority Pathogens List on Medical Mycology: A Northern European Perspective

Fungal diseases represent a considerable global health concern, affecting >1 billion people annually. In response to this growing challenge, the World Health Organization introduced the pivotal fungal priority pathogens list (FPPL) in late 2022. The FPPL highlights the challenges in estimating the global burden of fungal diseases and antifungal resistance (AFR), as well as limited surveillance capabilities and lack of routine AFR testing. Furthermore, training programs should incorporate sufficient information on fungal diseases, necessitating global advocacy to educate health care professionals and scientists. Established international guidelines and the FPPL are vital in strengthening local guidance on tackling fungal diseases. Future iterations of the FPPL have the potential to refine the list further, addressing its limitations and advancing our collective ability to combat fungal diseases effectively. Napp Pharmaceuticals Limited (Mundipharma UK) organized a workshop with key experts from Northern Europe to discuss the impact of the FPPL on regional clinical practice.

Candida tropicalis-A systematic review to inform the World Health Organization of a fungal priority pathogens list

In response to the growing global burden of fungal infections with uncertain impact, the World Health Organization (WHO) established an Expert Group to identify priority fungal pathogens and establish the WHO Fungal Priority Pathogens List for future research. This systematic review aimed to evaluate the features and global impact of invasive candidiasis caused by Candida tropicalis. PubMed and Web of Science were searched for studies reporting on criteria of mortality, morbidity (defined as hospitalization and disability), drug resistance, preventability, yearly incidence, diagnostics, treatability, and distribution/emergence from 2011 to 2021. Thirty studies, encompassing 436 patients from 25 countries were included in the analysis. All-cause mortality due to invasive C. tropicalis infections was 55%-60%. Resistance rates to fluconazole, itraconazole, voriconazole and posaconazole up to 40%-80% were observed but C. tropicalis isolates showed low resistance rates to the echinocandins (0%-1%), amphotericin B (0%), and flucytosine (0%-4%). Leukaemia (odds ratio (OR) = 4.77) and chronic lung disease (OR = 2.62) were identified as risk factors for invasive infections. Incidence rates highlight the geographic variability and provide valuable context for understanding the global burden of C. tropicalis infections. C. tropicalis candidiasis is associated with high mortality rates and high rates of resistance to triazoles. To address this emerging threat, concerted efforts are needed to develop novel antifungal agents and therapeutic approaches tailored to C. tropicalis infections. Global surveillance studies could better inform the annual incidence rates, distribution and trends and allow informed evaluation of the global impact of C. tropicalis infections.

Carbon substrates promotes stress resistance and drug tolerance in clinical isolates of Candida tropicalis

Candida tropicalis is a human pathogen and one of the most prevalent non-Candida albicans Candida (NCAC) species causing invasive infections. Azole antifungal resistance in C. tropicalis is also gradually increasing with the increasing incidence of infections. The pathogenic success of C. tropicalis depends on its effective response in the host microenvironment. To become a successful pathogen, cellular metabolism, and physiological status determine the ability of the pathogen to counter diverse stresses inside the host. However, to date, limited knowledge is available on the impact of carbon substrate metabolism on stress adaptation and azole resistance in C. tropicalis. In this study, we determined the impact of glucose, fructose, and sucrose as the sole carbon source on the fluconazole resistance and osmotic (NaCl), oxidative (H2O2) stress adaptation in C. tropicalis clinical isolates. We confirmed that the abundance of carbon substrates influences or increases drug resistance and osmotic and oxidative stress tolerance in C. tropicalis. Additionally, both azole-resistant and susceptible isolates showed similar stress adaptation phenotypes, confirming the equal efficiency of becoming successful pathogens irrespective of drug susceptibility profile. To the best of our knowledge, our study is the first on C. tropicalis to demonstrate the direct relation between carbon substrate metabolism and stress tolerance or drug resistance.

Clinical Distribution and Drug Susceptibility Characterization of Invasive Candida Isolates in a Tertiary Hospital of Xinjiang Province

Objective

This study aims to investigate the clinical distribution characteristics and drug susceptibility profiles of invasive Candida isolates in a tertiary hospital in Urumqi.

Methods

The examination was conducted on samples obtained from patients who were clinically diagnosed with invasive candidiasis in this hospital. A total of 109 strains of Candida strains were identified through the use of internal transcribed spacer (ITS) sequencing and fungal cultivation methods.The clinical distribution of the strains was analyzed. Antifungal drug susceptibility tests were performed using the Sensititre YO10 fungal drug susceptibility plate based on the micro-broth dilution method.

Results

Candida albicans had the highest percentage (51.38%) among 109 Candida isolates, followed by C. glabrata (18.35%) and C. tropicalis (15.60%). The isolates were predominantly found in the respiratory department (41.28%), intensive care unit (ICU) (31.19%), and infection department (9.17%).The results of drug susceptibility tests indicated that amphotericin B, 5-fluorocytosine, and echinocandins exhibited good in vitro antifungal activity, with a susceptibility rate of over 96%. However, the azoles demonstrated low antifungal activity, especially posaconazole and voriconazole, which had high resistance rates of 64.71% for C. tropicalis and 70% for C. glabrata, respectively.

Conclusion

In our hospital, Candida albicans was identified as the primary causal agent of invasive candidiasis. In terms of in vitro antifungal activity, echinocandins, amphotericin B, and 5-fluorocytosine demonstrated efficacy against invasive Candida infections. However, it was important to note that C. glabrata and C. tropicalis exhibited low susceptibility to azoles.

Tandem gene duplications contributed to high-level azole resistance in a rapidly expanding Candida tropicalis population

Invasive diseases caused by the globally distributed commensal yeast Candida tropicalis are associated with mortality rates of greater than 50%. Notable increases of azole resistance have been observed in this species, particularly within Asia-Pacific regions. Here, we carried out a genetic population study on 1571 global C. tropicalis isolates using multilocus sequence typing (MLST). In addition, whole-genome sequencing (WGS) analysis was conducted on 629 of these strains, comprising 448 clinical invasive strains obtained in this study and 181 genomes sourced from public databases. We found that MLST clade 4 is the predominant azole-resistant clone. WGS analyses demonstrated that dramatically increasing rates of azole resistance are associated with a rapid expansion of cluster AZR, a sublineage of clade 4. Cluster AZR isolates exhibited a distinct high-level azole resistance, which was induced by tandem duplications of the ERG11A395T gene allele. Ty3/gypsy-like retrotransposons were found to be highly enriched in this population. The alarming expansion of C. tropicalis cluster AZR population underscores the urgent need for strategies against growing threats of antifungal resistance.

Transcriptional Reprogramming of Candida tropicalis in Response to Isoespintanol Treatment

Candida tropicalis, an opportunistic pathogen, ranks among the primary culprits of invasive candidiasis, a condition notorious for its resistance to conventional antifungal drugs. The urgency to combat these drug-resistant infections has spurred the quest for novel therapeutic compounds, with a particular focus on those of natural origin. In this study, we set out to evaluate the impact of isoespintanol (ISO), a monoterpene derived from Oxandra xylopioides, on the transcriptome of C. tropicalis. Leveraging transcriptomics, our research aimed to unravel the intricate transcriptional changes induced by ISO within this pathogen. Our differential gene expression analysis unveiled 186 differentially expressed genes (DEGs) in response to ISO, with a striking 85% of these genes experiencing upregulation. These findings shed light on the multifaceted nature of ISO's influence on C. tropicalis, spanning a spectrum of physiological, structural, and metabolic adaptations. The upregulated DEGs predominantly pertained to crucial processes, including ergosterol biosynthesis, protein folding, response to DNA damage, cell wall integrity, mitochondrial activity modulation, and cellular responses to organic compounds. Simultaneously, 27 genes were observed to be repressed, affecting functions such as cytoplasmic translation, DNA damage checkpoints, membrane proteins, and metabolic pathways like trans-methylation, trans-sulfuration, and trans-propylamine. These results underscore the complexity of ISO's antifungal mechanism, suggesting that it targets multiple vital pathways within C. tropicalis. Such complexity potentially reduces the likelihood of the pathogen developing rapid resistance to ISO, making it an attractive candidate for further exploration as a therapeutic agent. In conclusion, our study provides a comprehensive overview of the transcriptional responses of C. tropicalis to ISO exposure. The identified molecular targets and pathways offer promising avenues for future research and the development of innovative antifungal therapies to combat infections caused by this pathogenic yeast.

Clonal aggregation of fluconazole-resistant Candida tropicalis isolated from sterile body fluid specimens from patients in Hefei, China

Candida tropicalis, a human conditionally pathogenic yeast, is distributed globally, especially in Asia-Pacific. The increasing morbidity and azole resistance of C. tropicalis have made clinical treatment difficult. The correlation between clonality and antifungal susceptibility of clinical C. tropicalis isolates has been reported. To study the putative correlation in C. tropicalis isolated from normally sterile body fluid specimens and explore the distinct clonal complex (CC) in Hefei, 256 clinical C. tropicalis isolates were collected from four teaching hospitals during 2016-2019, of which 30 were fluconazole-resistant (FR). Genetic profiles of 63 isolates, including 30 FR isolates and 33 fluconazole-susceptible (FS) isolates, were characterized using multilocus sequence typing (MLST). Phylogenetic analysis of the data was conducted using UPGMA (unweighted pair group method with arithmetic averages) and the minimum spanning tree algorithm. MLST clonal complexes (CCs) were analyzed using the goeBURST package. Among 35 differentiated diploid sequence types (DSTs), 16 DSTs and 1 genotype were identified as novel. A total of 35 DSTs were assigned to five major CCs based on goeBURST analysis. CC1 (containing DST376, 505, 507, 1221, 1222, 1223, 1226, and 1229) accounted for 86.7% (26/30) of the FR isolates. However, the genetic relationships among the FS isolates were relatively decentralized. The local FR CC1 belongs to a large fluconazole non-susceptible CC8 in global isolates, of which the putative founder genotype was DST225. The putative correlation between MLST types and antifungal susceptibility of clinical C. tropicalis isolates in Hefei showed that DSTs are closely related to FR clones.

Biofilm Formation in Medically Important Candida Species

Worldwide, the number of infections caused by biofilm-forming fungal pathogens is very high. In human medicine, there is an increasing proportion of immunocompromised patients with prolonged hospitalization, and patients with long-term inserted drains, cannulas, catheters, tubes, or other artificial devices, that exhibit a predisposition for colonization by biofilm-forming yeasts. A high percentage of mortality is due to candidemia caused by medically important Candida species. Species of major clinical significance include C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, and C. auris. The association of these pathogenic species in the biofilm structure is a serious therapeutic problem. Candida cells growing in the form of a biofilm are able to resist persistent therapy thanks to a combination of their protective mechanisms and their ability to disseminate to other parts of the body, thus representing a threat from the perspective of a permanent source of infection. The elucidation of the key mechanisms of biofilm formation is essential to progress in the understanding and treatment of invasive Candida infections.

Expression of ERG11, ERG3, MDR1 and CDR1 genes in Candida tropicalis

INTRODUCTION

Drug resistance to azoles is a growing problem in the Candida genus.

OBJECTIVE

To analyze molecularly the genes responsible for fluconazole resistance in Candida tropicalis strains.

MATERIALS AND METHODS

Nineteen strains, with and without exposure to fluconazole, were selected for this study. The expression of MDR1, CDR1, ERG11, and ERG3 genes was analyzed in sensitive, dose-dependent sensitive, and resistant strains exposed to different concentrations of the antifungal drug.

RESULTS

MDR1, ERG11 and ERG3 genes were significantly overexpressed in the different sensitivity groups. CDR1 gene expression was not statistically significant among the studied groups. Seven of the eight fluconazole-resistant strains showed overexpression of one or more of the analyzed genes. In some dose-dependent sensitive strains, we found overexpression of CDR1, ERG11, and ERG3.

CONCLUSION

The frequency of overexpression of ERG11 and ERG3 genes indicates that they are related to resistance. However, the finding of dose-dependent resistant/sensitive strains without overexpression of these genes suggests that they are not exclusive to this phenomenon. More basic research is needed to study other potentially involved genes in the resistance mechanism to fluconazole.

High prevalence of fluconazole resistant Candida tropicalis among candiduria samples in China: An ignored matter of concern

Introduction

The rapid rise of azole resistance in Candida tropicalis causing invasive infections has become a public health concern; however, the prevalence of resistant isolates in urine samples was not well studied, because the clinical significance of candiduria was not unambiguous due to possible host colonization.

Methods

We performed a 12-year laboratory-based surveillance study of C. tropicalis causing either invasive infection or candiduria and studied their susceptibility profiles to common antifungal drugs. The complete coding domain sequence of the ERG11 gene was amplified in all fluconazole resistant isolates, and aligned with the wild-type sequence to detect nucleotide mutations.

Results

A total of 519 unique C. tropicalis strains isolates, 69.9% of which were isolated from urine samples and remaining 30.1% were invasive strains. Overall, 16.5% isolates were confirmed to be resistant to fluconazole, of which 91.9% were cross-resistant voriconazole. Of note, at the beginning of surveillance (2010-2011), the fluconazole resistance rates were low in both candiduria and invasive groups (6.8% and 5.9%, respectively). However, the resistant rate in the candiduria group significantly increased to 29.5% since 2012-2013 (p = 0.001) and stayed high since then, whilst the resistance rate in the invasive group only showed a gradually increasing trends till 2021 (p > 0.05). Sequence analysis of ERG11 from fluconazole-resistant strains revealed the prevalence of A395T/W mutations were relatively low (16.7%) in the beginning but reached 87.5-100% after 2014. Moreover, the A395W heterozygous mutation isolates became predominant (>60% of resistant strains) after 2016, and indeed isolates carrying corresponding amino acid substitution (Y132F) was highly resistant to fluconazole with MIC₅₀ exceeded 256 μg/ml.

Conclusion

Our study revealed high azole resistant rate in candiduria with its increasing trends observed much earlier than stains causing invasive infections. Given antimicrobial resistance as a critical "One Health" issue, the emergence of antifungal resistance in Candida species that are common commensal colonizers in the human body should be concerned.

Non-albicans Candida Species: Immune Response, Evasion Mechanisms, and New Plant-Derived Alternative Therapies

Fungal infections caused by Candida species have become a constant threat to public health, especially for immunocompromised patients, who are considered susceptible to this type of opportunistic infections. Candida albicans is known as the most common etiological agent of candidiasis; however, other species, such as Candida tropicalis, Candida parapsilosis, Nakaseomyces glabrata (previously known as Candida glabrata), Candida auris, Candida guilliermondii, and Pichia kudriavzevii (previously named as Candida krusei), have also gained great importance in recent years. The increasing frequency of the isolation of this non-albicans Candida species is associated with different factors, such as constant exposure to antifungal drugs, the use of catheters in hospitalized patients, cancer, age, and geographic distribution. The main concerns for the control of these pathogens include their ability to evade the mechanisms of action of different drugs, thus developing resistance to antifungal drugs, and it has also been shown that some of these species also manage to evade the host's immunity. These biological traits make candidiasis treatment a challenging task. In this review manuscript, a detailed update of the recent literature on the six most relevant non-albicans Candida species is provided, focusing on the immune response, evasion mechanisms, and new plant-derived compounds with antifungal properties.

Distribution and antifungal susceptibility pattern of Candida species from mainland China: A systematic analysis

Antifungal resistance to Candida pathogens increases morbidity and mortality of immunosuppressive patients, an emerging crisis worldwide. Understanding the Candida prevalence and antifungal susceptibility pattern is necessary to control and treat candidiasis. We aimed to systematically analyse the susceptibility profiles of Candida species published in the last ten years (December 2011 to December 2021) from mainland China. The studies were collected from PubMed, Google Scholar, and Science Direct search engines. Out of 89 included studies, a total of 44,716 Candida isolates were collected, mainly comprising C. albicans (49.36%), C. tropicalis (21.89%), C. parapsilosis (13.92%), and C. glabrata (11.37%). The lowest susceptibility was detected for azole group; fluconazole susceptibilities against C. parapsilosis, C. albicans, C. glabrata, C. tropicalis, C. guilliermondii, C. pelliculosa, and C. auris were 93.25%, 91.6%, 79.4%, 77.95%, 76%, 50%, and 0% respectively. Amphotericin B and anidulafungin were the most susceptible drugs for all Candida species. Resistance to azole was mainly linked with mutations in ERG11, ERG3, ERG4, MRR1-2, MSH-2, and PDR-1 genes. Mutation in FKS-1 and FKS-2 in C. auris and C. glabrata causing resistance to echinocandins was stated in two studies. Gaps in the studies' characteristics were detected, such as 79.77%, 47.19 %, 26.97%, 7.86%, and 4.49% studies did not mention the mortality rates, age, gender, breakpoint reference guidelines, and fungal identification method, respectively. The current study demonstrates the overall antifungal susceptibility pattern of Candida species, gaps in surveillance studies and risk-reduction strategies that could be supportive in candidiasis therapy and for the researchers in their future studies.

Multilocus sequence typing (MLST) analysis reveals many novel genotypes and a high level of genetic diversity in Candida tropicalis isolates from Italy and Africa

BACKGROUND

Candida tropicalis is a human pathogenic yeast frequently isolated in Latin America and Asian-Pacific regions, although recent studies showed that it is also becoming increasingly widespread throughout several African and south-European countries. Nevertheless, relatively little is known about its global patterns of genetic variation as most of existing multilocus sequence typing (MLST) data come from Asia and there are no genotyped African isolates.

OBJECTIVES

We report detailed genotyping data from a large set of C. tropicalis isolates recovered from different clinical sources in Italy, Egypt and Cameroon in order to expand the allele/genotype library of MLST database (https://pubmlst.org/ctropicalis), and to explore the genetic diversity in this species.

METHODS

A total of 103 C. tropicalis isolates were genotyped using the MLST scheme developed for this species. All isolates were also tested for in vitro susceptibility to various antifungals to assess whether certain genotypes were associated with drug-resistance.

RESULTS AND CONCLUSIONS

A total of 104 different alleles were detected across the MLST-loci investigated. The allelic diversity found at these loci resulted in 51 unique MLST genotypes of which 36 (70.6%) were novel. Global optimal eBURST analysis identified 18 clonal complexes (CCs) and confirm the existence of a specific Italian-cluster (CC36). Three CCs were also statistically associated with fluconazole resistance, which was elevated in Cameroon and Egypt. Our data show high genetic diversity in our isolates suggesting that the global population structure of C. tropicalis is still poorly understood. Moreover, its clinical impact in Italy, Egypt and Cameroon appears to be relevant and should be carefully considered.

Time to Positivity Facilitates an Early Differential Diagnosis of Candida tropicalis from Other Candida species

Background

Candidemia caused by Candida tropicalis has more serious adverse consequences and an even higher mortality. Time to positivity (TTP) has been widely used to identify microbial species, resistant microorganisms and distinguish real pathogens and pollutants. However, few studies have demonstrated TTP as a presumptive diagnosis of C. tropicalis in patients with candidemia.

Patients and Methods

A retrospective study of 136 episodes of candidemia and simulated blood cultures with 314 episodes of confirmed Candida strains were applied to explore the role of TTPs in diagnosing C. tropicalis. TTPs were recorded as the shorter one if both aerobic and anaerobic vials were positive. Lastly, relationships were tested between TTPs and resistance and initial inocula concentration.

Results

For the retrospective study, the mean of TTPs for C. tropicalis from 136 patients with candidemia was significantly shorter than other Candida species. The area under the receiver operating characteristics (ROC) curve was 0.8896 ± 0.030 with a sensitivity of 92.86% and a specificity of 77.87%, respectively, indicating TTPs with a cut-off value of <25.50 h had a strong diagnostic power for C. tropicalis in patients with candidemia. Moreover, TTPs from 314 simulated blood cultures showed similar results as the retrospective study, demonstrating TTP is a powerful diagnostic tool in early diagnosing C. tropicalis in patients with candidemia. Additionally, our results showed no statistical significance between TTPs and initial inocula concentration and resistance of Candida species, suggesting initial inocula concentration does not impact TTPs, and TTPs may not be promising in predicting the resistance of all Candida species.

Conclusion

TTP can be employed to early distinguish C. tropicalis from other Candida species in patients with candidemia, which is extremely helpful to initiate empiric antifungal treatments to improve clinical outcomes.

Mechanisms of azole antifungal resistance in clinical isolates of Candida tropicalis

This study was designed to understand the molecular mechanisms of azole resistance in Candida tropicalis using genetic and bioinformatics approaches. Thirty-two azole-resistant and 10 azole-susceptible (S) clinical isolates of C. tropicalis were subjected to mutation analysis of the azole target genes including ERG11. Inducible expression analysis of 17 other genes potentially associated with azole resistance was also evaluated. Homology modeling and molecular docking analysis were performed to study the effect of amino acid alterations in mediating azole resistance. Of the 32 resistant isolates, 12 (37.5%) showed A395T and C461T mutations in the ERG11 gene. The mean overexpression of CDR1, CDR3, TAC1, ERG1, ERG2, ERG3, ERG11, UPC2, and MKC1 in resistant isolates without mutation (R-WTM) was significantly higher (p<0.05) than those with mutation (R-WM) and the sensitive isolates (3.2-11 vs. 0.2-2.5 and 0.3-2.2 folds, respectively). Although the R-WTM and R-WM had higher (p<0.05) CDR2 and MRR1 expression compared to S isolates, noticeable variation was not seen among the other genes. Protein homology modelling and molecular docking revealed that the mutations in the ERG11 gene were responsible for structural alteration and low binding efficiency between ERG11p and ligands. Isolates with ERG11 mutations also presented A220C in ERG1 and together T503C, G751A mutations in UPC2. Nonsynonymous mutations in the ERG11 gene and coordinated overexpression of various genes including different transporters, ergosterol biosynthesis pathway, transcription factors, and stress-responsive genes are associated with azole resistance in clinical isolates of C. tropicalis.

Epidemiology, Clinical Characteristics, Risk Factors, and Outcomes of Candidemia in a Large Tertiary Teaching Hospital in Western China: A Retrospective 5-Year Study from 2016 to 2020

The aim of this study was to investigate the current status of candidemia and evaluate the clinical characteristics, risk factors and outcomes among different species. We conducted a retrospective study by univariate and multivariate analysis between Candida albicans and non-albicans Candida (NAC) species in a Chinese national medical center from 2016 to 2020. Among the 259 episodes, C. albicans (38.6%) was the leading species, followed by C. tropicalis (24.3%), C. parapsilosis (20.5%), and C. glabrata (12.4%). Most C. albicans and C. parapsilosis were susceptible to nine tested antifungal agents, whereas C. tropicalis showed 30.2~65.9% resistance/non-wild-type to four azoles with great cross-resistance, indicating that fluconazole should not be used for empirical antifungal treatment. In multivariable models, the factor related to an increased risk of NAC was glucocorticoid exposure, whereas gastrointestinal hemorrhage and thoracoabdominal drainage catheters were associated with an increased risk in C. albicans. Subgroup analysis revealed leukemia and lymphoma, as well as glucocorticoid exposure, to be factors independently associated with C. tropicalis in comparison with C. albicans candidemia. No significant differences in 7-day mortality or 30-day mortality were observed between C. albicans and NAC. This study may provide useful information with respect to choosing empirical antifungal agents and exploring differences in molecular mechanisms.

Collateral consequences of agricultural fungicides on pathogenic yeasts: A One Health perspective to tackle azole resistance

Candida and Cryptococcus affect millions of people yearly, being responsible for a wide array of clinical presentations, including life-threatening diseases. Interestingly, most human pathogenic yeasts are not restricted to the clinical setting, as they are also ubiquitous in the environment. Recent studies raise concern regarding the potential impact of agricultural use of azoles on resistance to medical antifungals in yeasts, as previously outlined with Aspergillus fumigatus. Thus, we undertook a narrative review of the literature and provide lines of evidence suggesting that an alternative, environmental route of azole resistance, may develop in pathogenic yeasts, in addition to patient route. However, it warrants sound evidence to support that pathogenic yeasts cross border between plants, animals and humans and that environmental reservoirs may contribute to azole resistance in Candida or other yeasts for humans. As these possibilities could concern public health, we propose a road map for future studies under the One Health perspective.

Is Natural Population of Candida tropicalis Sexual, Parasexual, and/or Asexual?

Candida tropicalis is one of the most common opportunistic yeast pathogens of humans, especially prevalent in tropical and subtropical regions. This yeast has broad ecological distributions, can be found in both terrestrial and aquatic ecosystems, including being associated with a diversity of trees, animals, and humans. Evolutionary theory predicts that organisms thriving in diverse ecological niches likely have efficient mechanisms to generate genetic diversity in nature. Indeed, abundant genetic variations have been reported in natural populations (both environmental and clinical) of C. tropicalis. However, at present, our understanding on how genetic diversity is generated in natural C. tropicalis population remains controversial. In this paper, I review the current understanding on the potential modes of reproduction in C. tropicalis. I describe expectations of the three modes of reproduction (sexual, parasexual, and asexual) and compare them with the observed genotypic variations in natural populations. Though sexual and parasexual reproduction cannot be excluded, the analyses suggest asexual reproduction alone could explain all the observations reported so far. The results here have implications for understanding the evolution and epidemiology of C. tropicalis and other related human fungal pathogens.

Azole and echinocandin resistance mechanisms and genotyping of Candida tropicalis in Japan: cross-boundary dissemination and animal-human transmission of C. tropicalis infection

OBJECTIVES

To assess the prevalence and genetic basis of antifungal resistance mechanisms as well as the genotyping of Candida tropicalis from clinical and non-clinical sources in Japan.

METHODS

Eighty C. tropicalis isolates, including 32 clinical isolates recovered from 29 patients and 48 non-clinical isolates recovered from 24 different sources (animals and the environment) were evaluated. All isolates were tested phenotypically for resistance to a wide range of antifungals and genotypically for resistance mechanisms to azole and echinocandin. Furthermore, all the isolates were genotyped by multilocus sequence typing (MLST).

RESULTS

Phenotypically, 30.2% (16/53) of the isolates were azole-resistant, with high levels of azole resistance among clinical isolates (51.7%; 15/29) and low levels (4.2%; 1/24) among non-clinical isolates. None of the isolates were reported as echinocandin resistant, with 60.4% (32/53) of the isolates intermediate to caspofungin. Azole resistance was basically attributed to high expression levels of drug efflux transporter genes (CDR2 and CDR3), transcription factors (TAC1 and UPC2) and ergosterol biosynthesis pathway HMG gene. No FKS1 hot spot 1 (HS1) or HS2 missense mutations were detected in any of the isolates. MLST analysis revealed 36 different sequence types (STs), with the first identification of 23 new STs. Phylogenetic analysis confirmed the close relationship between the clinical and non-clinical isolates, with identifications of ST232 and ST933 among patients and marine mammals.

CONCLUSION

Our results confirmed the emergence of azole resistance in C. tropicalis in Japan. Furthermore, phylogenetic analysis confirmed the transboundary dissemination and cross-transmission of C. tropicalis between humans and animals.

Population pharmacokinetic model-guided optimization of intravenous voriconazole dosing regimens in critically ill patients with liver dysfunction

STUDY OBJECTIVES

This study aimed to establish a population pharmacokinetic (PPK) model of intravenous voriconazole (VRC) in critically ill patients with liver dysfunction and to explore the optimal dosing strategies in specific clinical scenarios for invasive fungal infections (IFIs) caused by common Aspergillus and Candida species.

DESIGN

Prospective pharmacokinetics study.

SETTING

The intensive care unit in a tertiary-care medical center.

PATIENTS

A total of 297 plasma VRC concentrations from 26 critically ill patients with liver dysfunction were included in the PPK analysis.

METHODS

Model-based simulations with therapeutic range of 2-6 mg/L as the plasma trough concentration (C_min ) target and the free area under the concentration-time curve from 0 to 24 h (ƒAUC₂₄ ) divided by the minimum inhibitory concentration (MIC) (ie, ƒAUC₂₄ /MIC) ≥25 as the effective target were performed to optimize VRC dosing regimens for Child-Pugh class A and B (CP-A/B) and Child-Pugh class C (CP-C) patients.

RESULTS

A two-compartment model with first-order elimination adequately described the data. Significant covariates in the final model were body weight on both central and peripheral distribution volume and Child-Pugh class on clearance. Intravenous VRC loading dose of 5 mg/kg every 12 h (q12h) for the first day was adequate for CP-A/B and CP-C patients to attain the C_min target at 24 h. The maintenance dose regimens of 100 mg q12h or 200 mg q24h for CP-A/B patients and 50 mg q12h or 100 mg q24h for CP-C patients could obtain the probability of effective target attainment of >90% at an MIC ≤0.5 mg/L and achieve the cumulative fraction of response of >90% against C. albicans, C. parapsilosis, C. glabrata, C. krusei, A. fumigatus, and A. flavus. Additionally, the daily VRC doses could be increased by 50 mg for CP-A/B and CP-C patients at an MIC of 1 mg/L, with plasma C_min monitored closely to avoid serious adverse events. It is recommended that an appropriate alternative antifungal agent or a combination therapy could be adopted when an MIC ≥2 mg/L is reported, or when the infection is caused by C. tropicalis but the MIC value is not available.

CONCLUSIONS

For critically ill patients with liver dysfunction, the loading dose of intravenous VRC should be reduced to 5 mg/kg q12h. Additionally, based on the types of fungal pathogens and their susceptibility to VRC, the adjusted maintenance dose regimens with lower doses or longer dosing intervals should be considered for CP-A/B and CP-C patients.

Virulence Factors and Azole-Resistant Mechanism of Candida Tropicalis Isolated from Candidemia

BACKGROUND

Limited knowledge exists on the virulence factors of Candida tropicalis and the mechanisms of azole resistance that lead to an intensified pathogenicity and treatment failure. We aimed to evaluate the virulence factors and molecular mechanisms of azole resistance among C. tropicalis isolated from patients with candidemia.

MATERIALS AND METHODS

Several virulence factors, including extracellular enzymatic activities, cell surface hydrophobicity (CSH), and biofilm formation, were evaluated. Antifungal susceptibility pattern and expression level of ERG11, UPC2, MDR1, and CDR1 genes of eight (4 fluconazole resistance and 4 fluconazole susceptible) clinical C. tropicalis isolates were assessed. The correlation between the virulence factors and antifungal susceptibility patterns was analyzed.

RESULTS

During a 4 year study, forty-five C. tropicalis isolates were recovered from candidemia patients. The isolates expressed different frequencies of virulence determinants as follows: coagulase 4 (8.9%), phospholipase 5 (11.1%), proteinase 31 (68.9%), esterase 43 (95.6%), hemolysin 44 (97.8%), biofilm formation 45 (100%) and CSH 45(100%). All the isolates were susceptible to amphotericin B and showed the highest resistance to voriconazole. There was a significant positive correlation between micafungin minimum inhibitory concentrations (MICs) and hemolysin production (r_s = 0.316). However, we found a negative correlation between fluconazole MICs and esterase production (r_s = -0.383). We observed the high expression of ERG11 and UPC2 genes in fluconazole-resistant C. tropicalis isolates.

CONCLUSION

C. tropicalis isolated from candidemia patients extensively displayed capacities for biofilm formation, hemolysis, esterase activity, and hydrophobicity. In addition, the overexpression of ERG11 and UPC2 genes was considered one of the possible mechanisms of azole resistance.

Species Distribution, Antifungal Susceptibility, and Molecular Epidemiology of Candida Species Causing Candidemia in a Tertiary Care Hospital in Bangkok, Thailand

Candida species represent a common cause of bloodstream infection (BSI). Given the emergence of non-albicans Candida (NAC) associated with treatment failure, investigations into the species distribution, fungal susceptibility profile, and molecular epidemiology of pathogens are necessary to optimize the treatment of candidemia and explore the transmission of drug resistance for control management. This study evaluated the prevalence, antifungal susceptibility, and molecular characteristics of Candida species causing BSI in a tertiary-level hospital in Bangkok, Thailand. In total, 54 Candida isolates were recovered from 49 patients with candidemia. C. tropicalis was the most prevalent species (33.3%), followed by C. albicans (29.6%). Most Candida species were susceptible to various antifungal agents, excluding C. glabrata and C. tropicalis, which had increased rates of non-susceptibility to azoles. Most C. glabrata isolates were non-susceptible to echinocandins, especially caspofungin. The population structure of C. albicans was highly diverse, with clade 17 predominance. GoeBURST analysis of C. tropicalis revealed associations between genotype and fluconazole resistance in a particular clonal complex. The population structure of C. glabrata appeared to have a low level of genetic diversity in MLST loci. Collectively, these data might provide a fundamental database contributing to the development of novel antifungal agents and diagnostic tests.

Continual Decline in Azole Susceptibility Rates in Candida tropicalis Over a 9-Year Period in China

Background

There have been reports of increasing azole resistance in Candida tropicalis, especially in the Asia-Pacific region. Here we report on the epidemiology and antifungal susceptibility of C. tropicalis causing invasive candidiasis in China, from a 9-year surveillance study.

Methods

From August 2009 to July 2018, C. tropicalis isolates (n = 3702) were collected from 87 hospitals across China. Species identification was carried out by mass spectrometry or rDNA sequencing. Antifungal susceptibility was determined by Clinical and Laboratory Standards Institute disk diffusion (CHIF-NET10-14, n = 1510) or Sensititre YeastOne (CHIF-NET15-18, n = 2192) methods.

Results

Overall, 22.2% (823/3702) of the isolates were resistant to fluconazole, with 90.4% (744/823) being cross-resistant to voriconazole. In addition, 16.9 (370/2192) and 71.7% (1572/2192) of the isolates were of non-wild-type phenotype to itraconazole and posaconazole, respectively. Over the 9 years of surveillance, the fluconazole resistance rate continued to increase, rising from 5.7 (7/122) to 31.8% (236/741), while that for voriconazole was almost the same, rising from 5.7 (7/122) to 29.1% (216/741), with no significant statistical differences across the geographic regions. However, significant difference in fluconazole resistance rate was noted between isolates cultured from blood (27.2%, 489/1799) and those from non-blood (17.6%, 334/1903) specimens (P-value < 0.05), and amongst isolates collected from medical wards (28.1%, 312/1110) versus intensive care units (19.6%, 214/1092) and surgical wards (17.9%, 194/1086) (Bonferroni adjusted P-value < 0.05). Although echinocandin resistance remained low (0.8%, 18/2192) during the surveillance period, it was observed in most administrative regions, and one-third (6/18) of these isolates were simultaneously resistant to fluconazole.

Conclusion

The continual decrease in the rate of azole susceptibility among C. tropicalis strains has become a nationwide challenge in China, and the emergence of multi-drug resistance could pose further threats. These phenomena call for effective efforts in future interventions.

Development and Application of a Multiple Cross Displacement Amplification Combined With Nanoparticle-Based Lateral Flow Biosensor Assay to Detect Candida tropicalis

Candida tropicalis is an increasingly opportunistic pathogen that causes serious invasive candidiasis threatening a patient’s life. Traditional methods to detect C. tropicalis infection depends on time-consuming, culture-based gold-standard methods. So, we sought to establish a new method that could detect target pathogens quickly, accurately, and straightforwardly. Herein, a combination of multiple cross displacement amplification (MCDA) and lateral flow biosensors (LFB) was employed to detect C. tropicalis. In the MCDA system, 10 primers were designed to identify the specific genes of C. tropicalis and amplify the genes in an isothermal amplification device. Then, MCDA amplification reaction products could be identified visibly by color change, and all the amplification products would be tested by LFB with no special equipment. The results demonstrated that the optimal reaction condition of C. tropicalis-MCDA assay was 64°C within 30 min, and only 10 fg DNA was required in each reaction. No cross-reaction was found between C. tropicalis strains and non-C. tropicalis strains. For 300 sputum samples, the results showed that MCDA-LFB assay could rapidly and successfully detect all of the C. tropicalis-positive (28/300) samples detected by the gold-standard method. The entire procedure, including specimen processing (40 min), isothermal reaction (30 min) and result reporting (within 2 min), could be completed within 75 min. Briefly, the study results demonstrated that the detection ability of C. tropicalis-MCDA-LFB assay was better than culture methods with more simplicity, rapidity, sensitivity and specificity. Hence, MCDA-LFB strategy is an effective tool to rapidly detect C. tropicalis in clinical samples, especially in resource-poor areas.

Activity and Mechanism of Action of Antifungal Peptides from Microorganisms: A Review

Harmful fungi in nature not only cause diseases in plants, but also fungal infection and poisoning when people and animals eat food derived from crops contaminated with them. Unfortunately, such fungi are becoming increasingly more resistant to traditional synthetic antifungal drugs, which can make prevention and control work increasingly more difficult to achieve. This means they are potentially very harmful to human health and lifestyle. Antifungal peptides are natural substances produced by organisms to defend themselves against harmful fungi. As a result, they have become an important research object to help deal with harmful fungi and overcome their drug resistance. Moreover, they are expected to be developed into new therapeutic drugs against drug-resistant fungi in clinical application. This review focuses on antifungal peptides that have been isolated from bacteria, fungi, and other microorganisms to date. Their antifungal activity and factors affecting it are outlined in terms of their antibacterial spectra and effects. The toxic effects of the antifungal peptides and their common solutions are mentioned. The mechanisms of action of the antifungal peptides are described according to their action pathways. The work provides a useful reference for further clinical research and the development of safe antifungal drugs that have high efficiencies and broad application spectra.

Antifungal susceptibility, genotyping, resistance mechanism, and clinical profile of Candida tropicalis blood isolates

Candida tropicalis is one of the major candidaemia agents, associated with the highest mortality rates among Candida species, and developing resistance to azoles. Little is known about the molecular mechanisms of azole resistance, genotypic diversity, and the clinical background of C. tropicalis infections. Consequently, this study was designed to address those questions. Sixty-four C. tropicalis bloodstream isolates from 62 patients from three cities in Iran (2014–2019) were analyzed. Strain identification, antifungal susceptibility testing, and genotypic diversity analysis were performed by MALDI-TOF MS, CLSI-M27 A3/S4 protocol, and amplified fragment length polymorphism (AFLP) fingerprinting, respectively. Genes related to drug resistance (ERG11, MRR1, TAC1, UPC2, and FKS1 hotspot9s) were sequenced. The overall mortality rate was 59.6% (37/62). Strains were resistant to micafungin [minimum inhibitory concentration (MIC) ≥1 μg/ml, 2/64], itraconazole (MIC > 0.5 μg/ml, 2/64), fluconazole (FLZ; MIC ≥ 8 μg/ml, 4/64), and voriconazole (MIC ≥ 1 μg/ml, 7/64). Pan-azole and FLZ + VRZ resistance were observed in one and two isolates, respectively, while none of the patients were exposed to azoles. MRR1 (T255P, 647S), TAC1 (N164I, R47Q), and UPC2 (T241A, Q340H, T381S) mutations were exclusively identified in FLZ-resistant isolates. AFLP fingerprinting revealed five major and seven minor genotypes; genotype G4 was predominant in all centers. The increasing number of FLZ-R C. tropicalis blood isolates and acquiring FLZ-R in FLZ-naive patients limit the efficiency of FLZ, especially in developing countries. The high mortality rate warrants reaching a consensus regarding the nosocomial mode of C. tropicalis transmission.

Candida tropicalis distribution and drug resistance is correlated with ERG11 and UPC2 expression

Background

Candida tropicalis (C. tropicalis) is an important opportunistic pathogenic Candida species that can cause nosocomial infection. In this study, we analyzed the distribution and drug susceptibility of C. tropicalis and the relationship between ERG11 and UPC2 expression and resistance to azole antifungal agents.

Methods

C. tropicalis was cultured and identified by Sabouraud Agar Medium, CHROM Agar Candida and ATB tests (Bio-Mérieux, France). Total RNA was extracted from the collected strains, and the ERG11 and UPC2 mRNA expression levels were analyzed by quantitative real-time PCR.

Results

In total, 2872 clinical isolates of Candida, including 319 strains of C. tropicalis, were analyzed herein; they were mainly obtained from the Departments of Respiratory Medicine and ICU. The strains were predominantly isolated from airway secretion samples, and the detection trend in four years was mainly related to the type of department and specimens. The resistance rates of C. tropicalis to fluconazole, itraconazole and voriconazole had been increasing year by year. The mRNA expression levels of ERG11 and UPC2 in the fluconazole-resistant group were significantly higher than they were in the susceptible group. In addition, there was a significant positive linear correlation between these two genes in the fluconazole-resistant group.

Conclusions

Overexpression of the ERG11 and UPC2 genes in C. tropicalis could increase resistance to azole antifungal drugs. The routine testing for ERG11 and UPC2 in high-risk patients in key departments would provide a theoretical basis for the rational application of azole antifungal drugs.

Population genomics of the pathogenic yeast Candida tropicalis identifies hybrid isolates in environmental samples

Candida tropicalis is a human pathogen that primarily infects the immunocompromised. Whereas the genome of one isolate, C. tropicalis MYA-3404, was originally sequenced in 2009, there have been no large-scale, multi-isolate studies of the genetic and phenotypic diversity of this species. Here, we used whole genome sequencing and phenotyping to characterize 77 isolates of C. tropicalis from clinical and environmental sources from a variety of locations. We show that most C. tropicalis isolates are diploids with approximately 2-6 heterozygous variants per kilobase. The genomes are relatively stable, with few aneuploidies. However, we identified one highly homozygous isolate and six isolates of C. tropicalis with much higher heterozygosity levels ranging from 36-49 heterozygous variants per kilobase. Our analyses show that the heterozygous isolates represent two different hybrid lineages, where the hybrids share one parent (A) with most other C. tropicalis isolates, but the second parent (B or C) differs by at least 4% at the genome level. Four of the sequenced isolates descend from an AB hybridization, and two from an AC hybridization. The hybrids are MTLa/α heterozygotes. Hybridization, or mating, between different parents is therefore common in the evolutionary history of C. tropicalis. The new hybrids were predominantly found in environmental niches, including from soil. Hybridization is therefore unlikely to be associated with virulence. In addition, we used genotype-phenotype correlation and CRISPR-Cas9 editing to identify a genome variant that results in the inability of one isolate to utilize certain branched-chain amino acids as a sole nitrogen source.

Rapid detection of ERG11 polymorphism associated azole resistance in Candida tropicalis

Increasing reports of azole resistance in Candida tropicalis, highlight the development of rapid resistance detection techniques. Nonsynonymous mutations in the lanosterol C14 alpha-demethylase (ERG11) gene is one of the predominant mechanisms of azole resistance in C. tropicalis. We evaluated the tetra primer-amplification refractory mutation system-PCR (T-ARMS-PCR), restriction site mutation (RSM), and high-resolution melt (HRM) analysis methods for rapid resistance detection based on ERG11 polymorphism in C. tropicalis. Twelve azole-resistant and 19 susceptible isolates of C. tropicalis were included. DNA sequencing of the isolates was performed to check the ERG11 polymorphism status among resistant and susceptible isolates. Three approaches T-ARMS-PCR, RSM, and HRM were evaluated and validated for the rapid detection of ERG11 mutation. The fluconazole MICs for the 12 resistant and 19 susceptible isolates were 32–256 mg/L and 0.5–1 mg/L, respectively. The resistant isolates showed A339T and C461T mutations in the ERG11 gene. The T-ARMS-PCR and RSM approaches discriminated all the resistant and susceptible isolates, whereas HRM analysis differentiated all except one susceptible isolate. The sensitivity, specificity, analytical sensitivity, time, and cost of analysis suggests that these three methods can be utilized for the rapid detection of ERG11 mutations in C. tropicalis. Additionally, an excellent concordance with DNA sequencing was noted for all three methods. The rapid, sensitive, and inexpensive T-ARMS-PCR, RSM, and HRM approaches are suitable for the detection of azole resistance based on ERG11 polymorphism in C. tropicalis and can be implemented in clinical setups for batter patient management.

Multilocus Sequence Typing Reveals Clonality of Fluconazole-Nonsusceptible Candida tropicalis: A Study From Wuhan to the Global

Candida tropicalis is a globally distributed human pathogenic yeast, and its increasing resistance to azoles makes clinical treatment difficult. In this study, we investigated the clinical features, azole resistance and genetic relatedness of 87 C. tropicalis isolates from central China and combined with the global database to explore the relationship between genetic information and fluconazole susceptibility. Of the 55 diploid sequence types (DSTs) identified by multilocus sequence typing (MLST), 27 DSTs were new to the C. tropicalis MLST database. Fluconazole-nonsusceptible (FNS) isolates were genetically closely related. goeBURST analysis showed that DST225, DST376, DST506, and DST546 formed a distinct and unique FNS clonal complex (CC) in Wuhan. The local FNS CC belongs to the large FNS CC (CC2) in China, in which the putative founder DST225 has been reported from the environment. The three most prevalent types (DST506, DST525, and DST546) in Wuhan had high minimum inhibitory concentrations (MICs) for antifungal azoles, and the six possible nosocomial transmissions we captured were all FNS strains, most of which were from CC2. Unique FNS CCs have been found in Singapore (CC8) and India (CC17) and are close to China's CC2 in the minimum spanning tree. There were no FNS CCs outside Asia. This study is the first to reveal a significant correlation between genetic information and fluconazole susceptibility worldwide and to trace geographical locations, which is of great value for molecular epidemiological surveillance and azole-resistance study of C. tropicalis globally.

Changes in Adhesion of Candida tropicalis Clinical Isolates Exhibiting Switch Phenotypes to Polystyrene and HeLa Cells

BACKGROUND

Candida tropicalis is an important human pathogen that can undergo multiple forms of phenotypic switching.

AIM

We aimed to evaluate the effect of phenotypic switching on the adhesion ability of C. tropicalis.

METHODS

C. tropicalis morphotypes included parental phenotypes (clinical isolates) and switch phenotypes (crepe, revertant of crepe-CR, rough, revertant of rough-RR, irregular center and revertant of irregular center-ICR). Adhesion to polystyrene and HeLa cells was determined by crystal violet assay. The percentage of HeLa cells with adhered yeasts and the number of adhered yeasts per HeLa cell were determined by light microscopy. Filamentation among adhered cells was assessed by direct counting.

RESULTS

On polystyrene, 60% of the switch strains showed difference (p < 0.05) on adhesion ability compared to their parental counterpart strains, and altered thickness of adhered cells layers. Filamentation was increased among adhered cells of the switched strains compared to parental strains. A positive correlation was observed between adhesion on polystyrene and filamentation for morphotypes of the system 49.07. The majority of the switched strains showed higher adhesion capability to HeLa cells in comparison to the adherence of the clinical strains. All revertant strains showed a higher number of yeast cells per HeLa cell compared to their variant counterparts (p < 0.05), with exception of the ICR.

CONCLUSIONS

Our findings indicate that switching events in C. tropicalis affect adhesion and filamentation of adhered cells on polystyrene and HeLa cells. The rise of switch strains with increased adhesion ability may contribute to the success of infection associated with C. tropicalis.

Molecular epidemiology of Candida tropicalis isolated from urogenital tract infections

Candida tropicalis is a common human pathogenic yeast, and its molecular typing is important for studying the population structure and epidemiology of this opportunistic yeast, such as epidemic genotype, population dynamics, nosocomial infection, and drug resistance surveillance. In this study, the antifungal susceptibility test and multilocus sequence typing (MLST) analysis were carried out on C. tropicalis from central China. Among 64 urogenital isolates, 45 diploid sequence types (DST) were found, of which 20 DSTs (44.4%) were new to the central database. The goeBURST analysis showed that CC1 (clonal complex) was the only azole‐resistant (100%, 10/10) cluster in Wuhan, which was composed of DST546, DST225, DST376, and DST506, and most of the strains (90%, 9/10) were isolated from the urinary tract. Potential nosocomial infections were mainly caused by CC1 strains. The azole resistance rate of urinary isolates (50.0%, 21/42) was higher than that of vaginal isolates (27.3%, 6/22). The genotype diversity and novelty of vaginal isolates were higher than those of urinary isolates. C. tropicalis population in Wuhan was genetically diverse and divergent from that seen in other countries. In this study, there were significant differences in genotype and azole susceptibility between urine and vaginal strains. The azole‐resistant cluster (CC1) found in urine is of great significance for the clinical treatment and prevention of nosocomial infection. The newly discovered DSTs will contribute to further study the similarity, genetic relationship, and molecular epidemiology of C. tropicalis worldwide.

The Quiet and Underappreciated Rise of Drug-Resistant Invasive Fungal Pathogens

Human fungal pathogens are attributable to a significant economic burden and mortality worldwide. Antifungal treatments, although limited in number, play a pivotal role in decreasing mortality and morbidities posed by invasive fungal infections (IFIs). However, the recent emergence of multidrug-resistant Candida auris and Candida glabrata and acquiring invasive infections due to azole-resistant C. parapsilosis, C. tropicalis, and Aspergillus spp. in azole-naïve patients pose a serious health threat considering the limited number of systemic antifungals available to treat IFIs. Although advancing for major fungal pathogens, the understanding of fungal attributes contributing to antifungal resistance is just emerging for several clinically important MDR fungal pathogens. Further complicating the matter are the distinct differences in antifungal resistance mechanisms among various fungal species in which one or more mechanisms may contribute to the resistance phenotype. In this review, we attempt to summarize the burden of antifungal resistance for selected non-albicansCandida and clinically important Aspergillus species together with their phylogenetic placement on the tree of life. Moreover, we highlight the different molecular mechanisms between antifungal tolerance and resistance, and comprehensively discuss the molecular mechanisms of antifungal resistance in a species level.

Species Distribution and Antifungal Susceptibility of Invasive Candidiasis: A 2016-2017 Multicenter Surveillance Study in Beijing, China

OBJECTIVE

Invasive candidiasis (IC), a life-threatening fungal infection prevalent among hospitalized patients, has highly variable regional epidemiology. We conducted a multicenter surveillance study to investigate recent trends in species distribution and antifungal susceptibility patterns among IC-associated Candida spp. in Beijing, China, from 2016 to 2017.

MATERIALS AND METHODS

A total of 1496 non-duplicate Candida isolates, recovered from blood and other sterile body fluids of IC patients, were identified using matrix-assisted laser desorption/ionization time of flight mass spectrometry combined with ribosomal DNA internal transcribed spacer (ITS) region sequencing. Broth microdilution-based susceptibility testing using six antifungal agents was also conducted.

RESULTS

Candida albicans was the most frequently isolated species (49.9%), followed by Candida tropicalis (15.5%), Candida glabrata (14.7%) and Candida parapsilosis (14.2%). No significant differences in species distribution were observed when compared with a 2012-2013 dataset. Overall, the rates of susceptibility to fluconazole and voriconazole were high among C. albicans (98% and 97.2%, respectively) and C. parapsilosis species complex (91.1% and 92%, respectively) isolates but low among C. tropicalis (81.5% and 81.1%, respectively) isolates. In addition, the rate of azole resistance among C. tropicalis isolates increased significantly (1.8-fold, P<0.05) compared with that observed in 2012-2013, while micafungin resistance rates were <5% for all tested Candida species.

CONCLUSION

Our results suggest that species distribution has remained stable among IC-associated Candida isolates in Beijing. Resistance to micafungin was rare, but increased azole resistance among C. tropicalis isolates was noted. Our study provides information on local epidemiology that will be important for the selection of empirical antifungal agents and contributes to global assessments of antifungal resistance.

Echinocandins versus Amphotericin B Against Candida tropicalis Fungemia in Adult Hematological Patients with Neutropenia: A Multicenter Retrospective Cohort Study

Background

Candida tropicalis is the most common non-albicans Candida species identified in immunocompromised patients, which often appears with high mortality. However, data on the outcomes of treatment for Candida tropicalis fungemia in patients with neutropenia remain limited.

Methods

In the present study, 90 neutropenic adult patients with proven Candida tropicalis fungemia, who received initial antifungal therapy, were retrospectively analyzed.

Results

These results revealed that the overall 8-day and 30-day mortality among patients in the entire data set were 22.2% and 33.3%, respectively. However, there was no significant difference between the survival and death group, in terms of baseline characteristics. The univariate analysis of risk factors identified the treatment with azole as a predictor of mortality, while treatments that containing amphotericin B were associated with reduced mortality. In addition, the survival rate on day 30 was observed in 60.7% (17/28) of patients who were initially treated with echinocandins, while this was observed in 86.4% (19/22, P=0.039) and 100% (13/13, P=0.024) of patients treated with amphotericin B plus echinocandins and amphotericin B, respectively.

Conclusion

These data indicate for the first time that the initial therapy with amphotericin B-based agents was associated with a better survival rate and could be assessed as the optimal strategy for the treatment of Candida tropicalis fungemia in patients with neutropenia.

Prevalence and Antifungal Susceptibility of Pathogenic Yeasts in China: A 10-Year Retrospective Study in a Teaching Hospital

To determine the dynamic changes of pathogenic yeast prevalence and antifungal susceptibility patterns in tertiary hospitals in China, we analyzed 527 yeast isolates preserved in the Research Center for Medical Mycology at Peking University, Beijing, China, between Jan 2010 and Dec 2019 and correctly identified 19 yeast species by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and ribosomal DNA sequencing. Antifungal susceptibility testing was performed following a Sensititre YeastOne colorimetric microdilution panel with nine clinically available antifungals. The Clinical and Laboratory Standards Institute (CLSI)-approved standard M27-A3 (S4) and newly revised clinical breakpoints or species-specific and method-specific epidemiological cutoff values were used for the interpretation of susceptibility test data. In this study, although Candida albicans was the predominant single species, non-C. albicans species constituted >50% of isolates in 6 out of 10 years, and more rare species were present in the recent 5 years. The non-C. albicans species identified most frequently were Candida parapsilosis sensu stricto, Candida tropicalis, and Candida glabrata. The prevalence of fluconazole and voriconazole resistance in the C. parapsilosis sensu stricto population was <3%, but C. tropicalis exhibited decreased susceptibility to fluconazole (42, 57.5%) and voriconazole (31, 42.5%), and 22 (30.1%) C. tropicalis isolates exhibited wild-type minimum inhibitory concentrations (MICs) to posaconazole. Furthermore, fluconazole and voriconazole cross-resistance prevalence in C. tropicalis was 19 (26.1%). The overall prevalence of fluconazole resistance in the C. glabrata population was 14 (26.9%), and prevalence of isolates exhibiting voriconazole non-wild-type MICs was 33 (63.5%). High-level echinocandin resistance was mainly observed in C. glabrata, and the prevalence rates of isolate resistance to anidulafungin, micafungin, and caspofungin were 5 (9.6%), 5 (9.6%), and 4 (7.7%), respectively. Moreover, one C. glabrata isolate showed multidrug resistant to azoles, echinocandins, and flucytosine. Overall, the 10-year surveillance study showed the increasing prevalence of non-C. albicans species over time; the emergence of azole resistance in C. tropicalis and multidrug resistance in C. glabrata over the years reinforced the need for epidemiological surveillance and monitoring.

An Association of an eBURST Group With Triazole Resistance of Candida tropicalis Blood Isolates

Candidemia, a bloodstream infection caused by genus Candida, has a high mortality rate. Candida albicans was previously reported to be the most common causative species among candidemia patients. However, during the past 10 years in Thailand, Candida tropicalis has been recovered from blood more frequently than C. albicans. The cause of this shift in the prevalence of Candida spp. remains unexplored. We conducted in vitro virulence studies and antifungal susceptibility profiles of 48 C. tropicalis blood isolates collected during 2015-2017. To compare to global isolates of C. tropicalis, multilocus sequence typing (MLST), a minimum spanning tree, and an eBURST analysis were also conducted. C. tropicalis and C. albicans were the most (47-48.7%) and second-most (21.5-33.9%) common species to be isolated from candidemia patients, respectively. Of the C. tropicalis blood isolates, 29.2, 0, 100, and 93.8% exhibited proteinase activity, phospholipase activity, hemolytic activity, and biofilm formation, respectively. Moreover, 20.8% (10/48) of the isolates were resistant to voriconazole and fluconazole, and also showed high minimum inhibitory concentrations (MICs) to posaconazole and itraconazole. In contrast, most of the isolates were susceptible to anidulafungin (97.9%), micafungin (97.9%), and caspofungin (97.9%), and showed low MICs to amphotericin B (100%) and 5-flucytosine (100%). The MLST identified 22 diploid sequence types. Based on the eBURST analysis and minimum spanning tree, 9 out of 13 members (69.2%) of an eBURST group 3 were resistant to voriconazole and fluconazole, and also showed high MICs to posaconazole and itraconazole. Association analysis revealed the eBURST group 3 was significantly associated with the four triazole resistance (p < 0.001). In conclusion, the eBURST group 3 was associated with the triazole resistance and resistance to many antifungal drugs might be collectively responsible for the prevalence shift.

Diclofenac exhibits synergism with azoles against planktonic cells and biofilms of Candida tropicalis

This study aimed to evaluate the effect of diclofenac on minimum inhibitory concentrations of antifungals against planktonic cells and biofilms of Candida tropicalis. Susceptibility testing of planktonic cells was evaluated using the broth microdilution assay and checkerboard method. Biofilm formation by C. tropicalis in the presence of diclofenac, alone or in combination with antifungals, was also evaluated, and scanning electron microscope (SEM) and confocal microscope (CLSM) analyses were performed. Diclofenac showed an MIC of 1024 μg ml^-1 against planktonic cells. The MICs of fluconazole and voriconazole against azole-resistant isolates were reduced 8- to 32-fold and 16- to 256-fold, respectively, when in combination with diclofenac. When in combination with fluconazole or voriconazole, diclofenac reduced the antifungal concentration necessary to inhibit C. tropicalis biofilm formation. In conclusion, diclofenac presents synergism with fluconazole and voriconazole against resistant C. tropicalis strains and improves the activity of these azole drugs against biofilm formation.

Dynamics of in vitro development of azole resistance in Candida tropicalis

OBJECTIVES

Increasing incidence of azole resistance in Candida tropicalis, especially to fluconazole, has been seen in Asian countries including India. Limited knowledge is available on the molecular mechanisms associated with the development of azole resistance in C. tropicalis. The present study examined the dynamics of in vitro azole resistance in C. tropicalis after prolonged treatment with fluconazole.

METHODS

Nine fluconazole-susceptible isolates of C. tropicalis were used in this study. Fluconazole resistance was induced experimentally in C. tropicalis isolates. The stability of induced resistance and cross-resistance to other azoles was examined. The molecular mechanisms of azole resistance were assessed by measuring the expression and mutation analysis of different genes.

RESULTS

Varying degrees of resistance [five with minimum inhibitory concentrations (MICs) ≤32 mg/L and four with MICs ≥128 mg/L] were noticed, and the resistance was developed in 3 months. Of the nine resistant isolates, four induced resistant isolates with MICs ≥128 mg/L presented temporal resistance stability up to 10 subcultures. These four isolates presented cross-resistance to other azoles and also an inducible overexpression of transporters (CDR1, CDR2, CDR3 and MDR1), ergosterol biosynthesis pathway genes (ERG1, ERG2, ERG3 and ERG11), transcription factors (TAC1 and UPC2) and stress-responsive genes (HSP90 and MKC1) was noticed. No mutations were seen in any of the four genes (ERG1, ERG3, ERG11 and UPC2) tested.

CONCLUSIONS

Candida tropicalis isolates adapt themselves in the presence of continuous drug exposure and switch back to being susceptible in the absence of the drug. The acquisition of resistance in C. tropicalis is mediated by the overexpression of different resistance-related genes without any molecular alterations.

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.

Candida tropicalis is the most prevalent yeast species causing candidemia in Algeria: the urgent need for antifungal stewardship and infection control measures

Background

Despite being associated with a high mortality and economic burden, data regarding candidemia are scant in Algeria. The aim of this study was to unveil the epidemiology of candidemia in Algeria, evaluate the antifungal susceptibility pattern of causative agents and understand the molecular mechanisms of antifungal resistance where applicable. Furthermore, by performing environmental screening and microsatellite typing we sought to identify the source of infection.

Methods

We performed a retrospective epidemiological-based surveillance study and collected available blood yeast isolates recovered from the seven hospitals in Algiers. To identify the source of infection, we performed environmental screening from the hands of healthcare workers (HCWs) and high touch areas. Species identification was performed by API Auxa-Color and MALDI-TOF MS and ITS sequencing was performed for species not reliably identified by MALDI-TOF MS. Antifungal susceptibility testing followed CLSI M27-A3/S4 and included all blood and environmental yeast isolates. ERG11 sequencing was performed for azole-resistant Candida isolates. Microsatellite typing was performed for blood and environmental Candida species, where applicable.

Results

Candida tropicalis (19/66) was the main cause of candidemia in these seven hospitals, followed by Candida parapsilosis (18/66), Candida albicans (18/66), and Candida glabrata (7/66). The overall mortality rate was 68.6% (35/51) and was 81.2% for C. tropicalis-infected patients (13/16). Fluconazole was the main antifungal drug used (12/51); 41% of the patients (21/51) did not receive any systemic treatment. Candida parapsilosis was isolated mainly from the hands of HCWs (7/28), and various yeasts were collected from high-touch areas (11/47), including Naganishia albida, C. parapsilosis and C. glabrata. Typing data revealed interhospital transmission on two occasions for C. parapsilosis and C. glabrata, and the same clone of C. parapsilosis infected two patients within the same hospital. Resistance was only noted for C. tropicalis against azoles (6/19) and fluconazole-resistant C. tropicalis isolates (≥8 μg/ml) (6/19) contained a novel P56S (5/6) amino acid substitution and a previously reported one (V234F; 1/6) in Erg11p.

Conclusions

Collectively, our data suggest an urgent need for antifungal stewardship and infection control strategies to improve the clinical outcome of Algerian patients with candidemia. The high prevalence of C. tropicalis joined by fluconazole-resistance may hamper the therapeutic efficacy of fluconazole, the frontline antifungal drug used in Algeria.

Distribution and Antifungal Susceptibility of Candida Species Causing Candidemia in China: An Update From the CHIF-NET Study

Background

Candidemia is the most common, serious fungal infection and Candida antifungal resistance is a challenge. We report recent surveillance of candidemia in China.

Methods

The study encompassed 77 Chinese hospitals over 3 years. Identification of Candida species was by mass spectrometry and DNA sequencing. Antifungal susceptibility was determined using the Clinical and Laboratory Standards Institute broth microdilution method.

Results

In total, 4010 isolates were collected from candidemia patients. Although C. albicans was the most common species, non-albicans Candida species accounted for over two-thirds of isolates, predominated C. parapsilosis complex (27.1%), C. tropicalis (18.7%), and C. glabrata complex (12.0%). Most C. albicans and C. parapsilosis complex isolates were susceptible to all antifungal agents (resistance rate &lt;5%). However, there was a decrease in voriconazole susceptibility to C. glabrata sensu stricto over the 3 years and fluconazole resistance rate in C. tropicalis tripled. Amongst less common Candida species, over one-third of C. pelliculosa isolates were coresistant to fluconazole and 5-flucytocine, and &gt;56% of C. haemulonii isolates were multidrug resistance.

Conclusions

Non-albicans Candida species are the predominant cause of candidemia in China. Azole resistance is notable amongst C. tropicalis and C. glabrata. Coresistance and multidrug resistance has emerged in less common Candida species.

Selection and evaluation of appropriate reference genes for RT-qPCR based expression analysis in Candida tropicalis following azole treatment

Candida tropicalis arises as one of the predominant non-Candida albicans Candida (NCAC) species causing invasive candidiasis in Asian countries. A rise in reports of C. tropicalis with a parallel increase in fluconazole resistance has also been observed. The genes and underlying pathways associated with azole antifungal resistance in C. tropicalis is still not properly understood. The RT-qPCR is the most promising approach for expression analysis of target genes to understand the mechanisms of resistance. The reliability and reproducibility of this technique depend on the selection of suitable reference genes for the normalization in expression study. The present study investigated the expression stability levels of ten genes including ACT1, EF1, GAPDH, PGK1, RDN5.8, RDN18, RDN28, SDHA, TUB1, and UBC13 for their suitability in fluconazole treated/untreated C. tropicalis. The stability levels of these genes were examined by the ∆∆CT, ΔCT, Pfaffl methods and five independent software including hkgFinder, geNorm, NormFinder, BestKeeper, and RefFinder software. We report, the EF1 and ACT1 were the most stable reference genes for normalization and can be used for the gene expression analysis in C. tropicalis. To the best of our knowledge, our study is the first to select and validate the reference genes in C. tropicalis for RT-qPCR based expression analysis.

Dear medical mycologists, it is time to look outside the box

Opulente et al. (Opulente DA, Langdon QK, Buh KV et al. Pathogenic budding yeasts isolated outside of clinical settings. FEMS Yeast Res 2019;19:foz032) published early this year a study aiming to investigate the diversity of wild yeast species, by collecting 1000 environmental samples coming from different substrates across the United States of America. The main finding of this work is the recovery of 54 strains of budding yeasts of which several are having a pathogenic potential in the clinical setting, such as Candida albicans, C. parapsilosis, C. tropicalis, Nakaseomyces glabrata and Pichia kudriavzevii. These findings, discussed here in light of other recent studies highlighting the role of fungicides in the rise of antifungal resistance in the clinical setting or the emergence of Candida auris, demonstrate that our environment can represent an alternative niche for several opportunistic fungal pathogens that can be a concern for human health.