Mechanisms of azole resistance in 52 clinical isolates of Candida tropicalis in China

Elucidation of the mechanisms of fluconazole resistance and repurposing treatment options against urinary Candida spp. isolated from hospitalized patients in Alexandria, Egypt

BACKGROUND

The incidence of fungal urinary tract infections (UTIs) has dramatically increased in the past decades, with Candida arising as the predominant etiological agent. Managing these infections poses a serious challenge to clinicians, especially with the emergence of fluconazole-resistant (FLC-R) Candida species. In this study, we aimed to determine the mechanisms of fluconazole resistance in urinary Candida spp. isolated from hospitalized patients in Alexandria, Egypt, assess the correlation between fluconazole resistance and virulence, and explore potential treatment options for UTIs caused by FLC-R Candida strains.

RESULTS

Fluconazole susceptibility testing of 34 urinary Candida isolates indicated that 76.5% were FLC-R, with a higher prevalence of resistance recorded in non-albicans Candida spp. (88.9%) than in Candida albicans (62.5%). The calculated Spearman's correlation coefficients implied significant positive correlations between fluconazole minimum inhibitory concentrations and both biofilm formation and phospholipase production. Real-time PCR results revealed that most FLC-R isolates (60%) significantly overexpressed at least one efflux pump gene, while 42.3% significantly upregulated the ERG11 gene. The most prevalent mutation detected upon ERG11 sequencing was G464S, which is conclusively linked to fluconazole resistance. The five repurposed agents: amikacin, colistin, dexamethasone, ketorolac, and sulfamethoxazole demonstrated variable fluconazole-sensitizing activities in vitro, with amikacin, dexamethasone, and colistin being the most effective. However, the fluconazole/colistin combination produced a notable reduction (49.1%) in bladder bioburden, a 50% decrease in the inflammatory response, and tripled the median survival span relative to the untreated murine models.

CONCLUSIONS

The fluconazole/colistin combination offers a promising treatment option for UTIs caused by FLC-R Candida, providing an alternative to the high-cost, tedious process of novel antifungal drug discovery in the battle against antifungal resistance.

Deletion of PMP3 increases ketoconazole resistance by affecting plasma membrane potential in Candida albicans

Ketoconazole is a classical antifungal drug commonly used in the clinic. With the increased use of ketoconazole in recent years, an increasing number of drug-resistant strains have emerged during clinical treatment. It is well known that fungi acquire drug resistance in multiple ways, while the molecular mechanisms underlying ketoconazole resistance remain for comprehensive exploration. In this study, we found that the expression of the small plasma membrane protein-encoding gene PMP3 was significantly down-regulated in several clinically isolated ketoconazole-resistant strains, indicating the relationship between PMP3 expression and ketoconazole resistance. By knocking out the PMP3, we found that the absence of the Pmp3 resulted in a significant increase in resistance of Candida albicans to ketoconazole, which was also confirmed in a systemic infection model in mice. We further demonstrated that various physiological properties, such as cell membrane fluidity, plasma membrane potential, permeability and ergosterol distribution were altered in the pmp3Δ/Δ mutant, which is associated with the enhanced cellular resistance to ketoconazole. In addition, overexpression rather than deletion of PMP3 alters the hyphal development and biofilm formation capacity in C. albicans. This study reveals the contribution of Pmp3 to alteration of drug resistance in fungal pathogens, which may guide the development of novel antifungal strategies.

Case Commentary: Extending our therapeutic range against multidrug-resistant Candida

Deep-seated Candida spp. infections may necessitate extended durations of antifungal therapy. Increasing resistance to first-line antifungals threatens the most common options for long-term treatment. In this issue, Ponta et al. (Antimicrob Agents Chemother 68:e00750-24, 2024, https://doi.org/10.1128/aac.00750-24) present cases in which they used rezafungin, a novel long-acting echinocandin antifungal, for extended durations. While excellent clinical evidence supports the short-term safety of rezafungin, these cases demonstrate that rezafungin may additionally have a role in long-term suppressive therapy for antifungal-resistant Candida spp. infections.

Analysis of CDR1 and MDR1 Gene Expression and ERG11 Substitutions in Clinical Candida tropicalis Isolates from Alexandria, Egypt

INTRODUCTION

Candida tropicalis is a common non-albicans Candida (NAC) species that causes numerous fungal infections. Increasing antifungal resistance to azoles in NAC is becoming a major health problem worldwide; however, in Egypt, almost no data is available regarding fluconazole resistance mechanisms in C. tropicalis. The current study aims to investigate two possible important molecular mechanisms involved in fluconazole resistance in C. tropicalis isolates.

MATERIALS

Fifty-four clinical C. tropicalis isolates were included. Identification and antifungal susceptibility profiles of the isolates were carried out using the VITEK 2 compact system. The molecular investigation of fluconazole resistance included the expression of the CDR1 and MDR1 genes by quantitative real-time RT-PCR as well as the sequence analysis of the ERG11 gene.

RESULTS

Antifungal susceptibility testing identified 30 fluconazole-non-susceptible isolates. Statistically, CDR1 gene expression in fluconazole-non-susceptible isolates was significantly higher than that in fluconazole-susceptible isolates, with MDR1 gene expression levels that were similar in both non-susceptible and susceptible isolates. Sequence analysis of the ERG11 gene of 26 fluconazole-resistant isolates identified two missense mutations: A395T (Y132F) and G1390A (G464S).

CONCLUSIONS

This study has highlighted the role of overexpression of the CDR1 gene and ERG11 gene mutations in fluconazole non-susceptibility. Further studies in Egypt are required to investigate other possible molecular mechanisms involved in azole resistance.

Antifungal resistance, combinations and pipeline: oh my!

Invasive fungal infections are a strong contributor to healthcare costs, morbidity and mortality, especially amongst hospitalized patients. Historically, Candida was responsible for approximately 15% of all nosocomial bloodstream infections. In the past 10 years, the epidemiology of Candida species has altered, with increasing prevalence of resistant species. With rising fungal resistance, especially in Candida spp., the demand for novel antifungal therapies has exponentially increased over the last decade. Newer antifungal agents have become an attractive option for patients needing long-term therapy for infections or those requiring antifungal prophylaxis. Despite advances in coverage of non-Candida pathogens with newer agents, clinical scenarios involving multidrug-resistant fungal pathogens continue to arise in practice. Combination antifungal therapy can lead to a host of side-effects, some of which can be drug limiting. Additional antifungal therapies with enhanced fungal spectrum of activity and decreased rates of adverse effects are warranted. Fosmanogepix, ibrexafungerp, olorofim and rezafungin may help fill some of these gaps in the antifungal armamentarium. This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

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.

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.

In Vivo Microevolutionary Analysis of a Fatal Case of Rhinofacial and Disseminated Mycosis Due to Azole-Drug-Resistant Candida Species

Ten Candida species strains were isolated from the first known fatal case of rhinofacial and rhino-orbital-cerebral candidiasis. Among them, five strains of Candida parapsilosis complex were isolated during the early stage of hospitalization, while five strains of Candida tropicalis were isolated in the later stages of the disease. Using whole-genome sequencing, we distinguished the five strains of C. parapsilosis complex as four Candida metapsilosis strains and one Candida parapsilosis strain. Antifungal susceptibility testing showed that the five strains of C. parapsilosis complex were susceptible to all antifungal drugs, while five C. tropicalis strains had high minimum inhibitory concentrations to azoles, whereas antifungal-drug resistance gene analysis revealed the causes of azole resistance in such strains. For the first time, we analyzed the microevolutionary characteristics of pathogenic fungi in human hosts and inferred the infection time and parallel evolution of C. tropicalis strains. Molecular clock analysis revealed that azole-resistant C. tropicalis infection occurred during the first round of therapy, followed by divergence via parallel evolution in vivo. The presence/absence variations indicated a potential decrease in the virulence of genomes in strains isolated following antifungal drug treatment, despite the absence of observed clinical improvement in the conditions of the patient. These results suggest that genomic analysis could serve as an auxiliary tool in guiding clinical diagnosis and treatment.

Genomic epidemiology of human candidaemia isolates in a tertiary hospital

Invasive candida infections are significant infections that may occur in vulnerable patients with high rates of mortality or morbidity. Drug-resistance rates also appear to be on the rise which further complicate treatment options and outcomes. The aims of this study were to describe the prevalence, molecular epidemiology, and genetic features of Candida bloodstream isolates in a hospital setting. The resistance mechanisms towards the two most commonly administered antifungals, fluconazole and anidulafungin, were determined. Blood culture isolates between 1 January 2018 and 30 June 2021 positive for Candida spp. were included. Susceptibility testing was performed using Etest. Whole-genome-sequencing was performed using Illumina NovaSeq with bioinformatics analysis performed. A total of 203 isolates were sequenced: 56 C. glabrata, 53 C. tropicalis, 44 C. albicans, 36 C. parapsilosis complex (consisting of C. parapsilosis, C. orthopsilosis, and C. metapsilosis), six C. krusei, five C. dubliniensis, and three C. auris. A single cluster of azole-resistant C. tropicalis, and four clusters of C. parapsilosis isolates were observed, suggesting possible transmission occurring over several years. We found 11.3%, and 52.7 % of C. tropicalis and C. parapsilosis, respectively, clustered with other isolates, suggesting exogenous sources may play a significant role of transmission, particularly for C. parapsilosis. The clusters spanned over several years suggesting the possibility of environmental reservoirs contributing to the spread. Limited clonality was seen for C. albicans. Several sequence types appeared to be dominant for C. glabrata, however the SNP differences varied widely, indicating absence of sustained transmission.

Anti-Candida albicans Effects and Mechanisms of Theasaponin E1 and Assamsaponin A

Candida albicans is an opportunistic human fungal pathogen, and its drug resistance is becoming a serious problem. Camellia sinensis seed saponins showed inhibitory effects on resistant Candida albicans strains, but the active components and mechanisms are unclear. In this study, the effects and mechanisms of two Camellia sinensis seed saponin monomers, theasaponin E1 (TE1) and assamsaponin A (ASA), on a resistant Candida albicans strain (ATCC 10231) were explored. The minimum inhibitory concentration and minimum fungicidal concentration of TE1 and ASA were equivalent. The time-kill curves showed that the fungicidal efficiency of ASA was higher than that of TE1. TE1 and ASA significantly increased the cell membrane permeability and disrupted the cell membrane integrity of C. albicans cells, probably by interacting with membrane-bound sterols. Moreover, TE1 and ASA induced the accumulation of intracellular ROS and decreased the mitochondrial membrane potential. Transcriptome and qRT-PCR analyses revealed that the differentially expressed genes were concentrated in the cell wall, plasma membrane, glycolysis, and ergosterol synthesis pathways. In conclusion, the antifungal mechanisms of TE1 and ASA included the interference with the biosynthesis of ergosterol in fungal cell membranes, damage to the mitochondria, and the regulation of energy metabolism and lipid metabolism. Tea seed saponins have the potential to be novel anti-Candida albicans agents.

Characterization of Virulence Factors in Candida Species Causing Candidemia in a Tertiary Care Hospital in Bangkok, Thailand

Candidemia is often associated with high mortality, and Candida albicans, Candida tropicalis, Candida glabrata, and Candida parapsilosis are common causes of this disease. The pathogenicity characteristics of specific Candida spp. that cause candidemia in Thailand are poorly understood. This study aimed to characterize the virulence factors of Candida spp. Thirty-eight isolates of different Candida species from blood cultures were evaluated for their virulence properties, including exoenzyme and biofilm production, cell surface hydrophobicity, tissue invasion, epithelial cell damage, morphogenesis, and phagocytosis resistance; the identity and frequency of mutations in ERG11 contributing to azole-resistance were also determined. C. albicans had the highest epithelial cell invasion rate and phospholipase activity, with true hyphae formation, whereas C. tropicalis produced the most biofilm, hydrophobicity, protease activity, and host cell damage and true hyphae formation. ERG11 mutations Y132F and S154F were observed in all azole-resistant C. tropicalis. C. glabrata had the most hemolytic activity while cell invasion was low with no morphologic transition. C. glabrata was more easily phagocytosed than other species. C. parapsilosis generated pseudohyphae but not hyphae and did not exhibit any trends in exoenzyme production. This knowledge will be crucial for understanding the pathogenicity of Candida spp. and will help to explore antivirulence-based treatment.

The Interkingdom Interaction with Staphylococcus Influences the Antifungal Susceptibility of the Cutaneous Fungus Malassezia

The skin is a dynamic ecosystem on which diverse microbes reside. The interkingdom interaction between microbial species in the skin microbiota is thought to influence the health and disease of the skin although the roles of the intra- and interkingdom interactions remain to be elucidated. In this context, the interactions between Malassezia and Staphylococcus, the most dominant microorganisms in the skin microbiota, have gained attention. This study investigated how the interaction between Malassezia and Staphylococcus affected the antifungal susceptibility of the fungus to the azole antifungal drug ketoconazole. The susceptibility was significantly decreased when Malassezia was co-cultured with Staphylococcus. We found that acidification of the environment by organic acids produced by Staphylococcus influenced the decrease of the ketoconazole susceptibility of M. restricta in the co-culturing condition. Furthermore, our data demonstrated that the significant increased ergosterol content and cell membrane and wall thickness of the M. restricta cells grown in the acidic environment may be the main cause of the altered azole susceptibility of the fungus. Overall, our study suggests that the interaction between Malassezia and Staphylococcus influences the antifungal susceptibility of the fungus and that pH has a critical role in the polymicrobial interaction in the skin environment.

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.

Similarities and Differences among Species Closely Related to Candida albicans: C. tropicalis, C. dubliniensis, and C. auris

Although Candida species are widespread commensals of the microflora of healthy individuals, they are also among the most important human fungal pathogens that under certain conditions can cause diseases (candidiases) of varying severity ranging from mild superficial infections of the mucous membranes to life-threatening systemic infections. So far, the vast majority of research aimed at understanding the molecular basis of pathogenesis has been focused on the most common species—Candida albicans. Meanwhile, other closely related species belonging to the CTG clade, namely, Candida tropicalis and Candida dubliniensis, are becoming more important in clinical practice, as well as a relatively newly identified species, Candida auris. Despite the close relationship of these microorganisms, it seems that in the course of evolution, they have developed distinct biochemical, metabolic, and physiological adaptations, which they use to fit to commensal niches and achieve full virulence. Therefore, in this review, we describe the current knowledge on C. tropicalis, C. dubliniensis, and C. auris virulence factors, the formation of a mixed species biofilm and mutual communication, the environmental stress response and related changes in fungal cell metabolism, and the effect of pathogens on host defense response and susceptibility to antifungal agents used, highlighting differences with respect to C. albicans. Special attention is paid to common diagnostic problems resulting from similarities between these species and the emergence of drug resistance mechanisms. Understanding the different strategies to achieve virulence, used by important opportunistic pathogens of the genus Candida, is essential for proper diagnosis and treatment.

Fluconazole-resistant Candida parapsilosis: A new emerging threat in the fungi arena

Candida parapsilosis is a leading cause of invasive candidiasis in southern Europe, Latin America and Asia. C. parapsilosis has been mostly considered susceptible to triazoles, but fluconazole resistance is on the rise in some countries. The main mechanism related to fluconazole resistance is the presence of ERG11p substitutions, dominated by the Y132F amino acid substitution. Isolates harbouring this substitution mimic C. auris given that they may cause hospital outbreaks, become endemic, and emerge simultaneously in distant areas around the world. At the moment, Spain is experiencing a brusque emergence of fluconazole resistance in C. parapsilosis; isolates harbouring the Y132F substitution were detected for the first time in 2019. A recent study on Candida spp isolates from blood cultures collected in 16 hospitals located in the Madrid metropolitan area (2019 to 2021) reported that fluconazole resistance in C. parapsilosis reached as high as 13.6%. Resistance rates rose significantly during those three years: 3.8% in 2019, 5.7% in 2020, and 29.1% in 2021; resistant isolates harboured either the dominant Y132F substitution (a single clone found in four hospitals) or G458S (another clone found in a fifth hospital). The COVID-19 pandemic may have increased the number of candidaemia cases. The reason for such an increase might be a consequence of uncontrolled intra-hospital patient-to-patient transmission in some hospitals, as an increase not only in C. parapsilosis candidaemia episodes but also in the spread of clonal fluconazole-resistant isolates might have occurred in other hospitals during the pandemic period. Patients affected with fluconazole-resistant C. parapsilosis harbouring the Y132F substitution presented a mortality rate ranging from 9% to 78%, were mainly admitted to intensive care wards but did not have differential risk factors compared to those infected by susceptible isolates. With scarce exceptions, few patients (≤20%) infected with fluconazole-resistant isolates had previously received fluconazole, thus supporting the fact that, although fluconazole might have been a key factor to promote resistance, the main driver promoting the spread of fluconazole-resistant isolates was patient-to-patient transmission.

Molecular identification, antifungal susceptibility, and resistance mechanisms of pathogenic yeasts from the China antifungal resistance surveillance trial (CARST-fungi) study

To have a comprehensive understanding of epidemiology and antifungal susceptibilities in pathogenic yeasts, the China Antifungal Resistance Surveillance Trial (CARST-fungi) study was conducted. All yeast isolates were identified by ribosomal DNA sequencing. Antifungal susceptibilities were performed using CLSI M27-A4 broth microdilution method. Sequence and expression level of resistant-related genes in resistant/non-wide-type (NWT) Candida isolates were analyzed. Totally 269 nonduplicate yeast isolates from 261 patients were collected. About half of the yeast isolates (127, 47.2%) were recovered from blood, followed by ascetic fluid (46, 17.1%). C. albicans remained the most prevalent (120, 44.6%), followed by C. parapsilosis complex (50, 18.6%), C. tropicalis (40, 14.9%), and C. glabrata (36, 13.4%). Fourteen (11.7%) C. albicans isolates and 1 (2.0%) C. parapsilosis isolate were resistant/NWT to triazoles. Only 42.5% (17/40) C. tropicalis were susceptible/WT to all the triazoles, with 19 (47.5%) isolates NWT to posaconazole and 8 (20%) cross-resistant to triazoles. Among C. glabrata, 20 (55.6%) and 8 (22.2%) isolates were resistant/NWT to voriconazole and posaconazole, respectively, and 4 (10.3%) isolates were cross-resistant to triazoles. Isavuconazole was the most active triazole against common Candida isolates. Except for 2 isolates of C. glabrata cross-resistant to echinocandins which were also NWT to POS and defined as multidrug-resistant, echinocandins exhibit good activity against common Candida species. All isolates were WT to AMB. For less common species, Rhodotorula mucilaginosa exhibited high MICs to echinocandins and FLC, and 1 isolate of Trichosporon asahii showed high MICs to all the antifungals except AMB. Among triazole-resistant Candida isolates, ERG11 mutations were detected in 10/14 C. albicans and 6/23 C. tropicalis, while 21/23 C. tropicalis showed MDR1 overexpression. Overexpression of CDR1, CDR2, and SNQ2 exhibited in 14, 13, and 8 of 25 triazole-resistant C. glabrata isolates, with 5 isolates harboring PDR1 mutations and 2 echinocandins-resistant isolates harboring S663P mutation in FKS2. Overall, the CARST-fungi study demonstrated that although C. albicans remain the most predominant species, non-C. albicans species accounted for a high proportion. Triazole-resistance is notable among C. tropicalis and C. glabrata. Multidrug-resistant isolates of C. glabrata and less common yeast have been emerging.

The Risk Factors and Mechanisms of Azole Resistance of Candida tropicalis Blood Isolates in Thailand: A Retrospective Cohort Study

In recent decades, an epidemiological shift has been observed from Candida infections to non-albicans species and resistance to azoles. We investigated the associated factors and molecular mechanisms of azole-resistant blood isolates of C. tropicalis. Full-length sequencing of the ERG11 gene and quantitative real-time RT-PCR for the ERG11, MDR1, and CDR1 genes were performed. Male sex (odds ratio, 0.38), leukemia (odds ratio 3.15), and recent administration of azole (odds ratio 10.56) were associated with isolates resistant to azole. ERG11 mutations were found in 83% of resistant isolates, with A395T as the most common mutation (53%). There were no statistically significant differences in the expression of the ERG11, MDR1, and CDR1 genes between the groups resistant and susceptible to azole. The prevalence of azole-resistant isolates was higher than the usage of antifungal drugs, suggesting the possibility of environmental transmission in the healthcare setting. The unknown mechanism of the other 17% of the resistant isolates remains to be further investigated.

Whole Genome Sequencing Shows Genetic Diversity, as Well as Clonal Complex and Gene Polymorphisms Associated with Fluconazole Non-Susceptible Isolates of Candida tropicalis

Resistance to azoles in Candida tropicalis is increasing and may be mediated by genetic characteristics. Using whole genome sequencing (WGS), we examined the genetic diversity of 82 bloodstream C. tropicalis isolates from two countries and one ATCC strain in a global context. Multilocus sequence typing (MLST) and single nucleotide polymorphism (SNP)-based phylogenies were generated. Minimum inhibitory concentrations (MIC) for antifungal agents were determined using Sensititre YeastOne YO10. Eleven (13.2%) isolates were fluconazole-resistant and 17 (20.5%) were classified as fluconazole-non susceptible (FNS). Together with four Canadian isolates, the genomes of 12 fluconazole-resistant (18 FNS) and 69 fluconazole-susceptible strains were examined for gene mutations associated with drug resistance. Fluconazole-resistant isolates contained a mean of 56 non-synonymous SNPs per isolate in contrast to 36 SNPs in fluconazole-susceptible isolates (interquartile range [IQR] 46−59 vs. 31−48 respectively; p < 0.001). Ten of 18 FNS isolates contained missense ERG11 mutations (amino acid substitutions S154F, Y132F, Y257H). Two echinocandin-non susceptible isolates had homozygous FKS1 mutations (S30P). MLST identified high genetic diversity with 61 diploid sequence types (DSTs), including 53 new DSTs. All four isolates in DST 773 were fluconazole-resistant within clonal complex 2. WGS showed high genetic variation in invasive C. tropicalis; azole resistance was distributed across different lineages but with DST 773 associated with in vitro fluconazole resistance.

The emerging threat antifungal-resistant Candida tropicalis in humans, animals, and environment

Antifungal resistance in humans, animals, and the environment is an emerging problem. Among the different fungal species that can develop resistance, Candida tropicalis is ubiquitous and causes infections in animals and humans. In Asia and some Latin American countries, C. tropicalis is among the most common species related to candidemia, and mortality rates are usually above 40%. Fluconazole resistance is especially reported in Asian countries and clonal spread in humans and the environment has been investigated in some studies. In Brazil, high rates of azole resistance have been found in animals and the environment. Multidrug resistance is still rare, but recent reports of clinical multidrug-resistant isolates are worrisome. The molecular apparatus of antifungal resistance has been majorly investigated in clinical C. tropicalis isolates, revealing that this species can develop resistance through the conjunction of different adaptative mechanisms. In this review article, we summarize the main findings regarding antifungal resistance and Candida tropicalis through an "One Health" approach.

Importance of Candida infection and fluconazole resistance in women with vaginal discharge syndrome in Namibia

BACKGROUND

Vaginal discharge syndrome (VDS) is a common condition. Clinical management targets sexually transmitted infections (STIs) and bacterial vaginosis (BV); there is limited focus on Candida infection as cause of VDS. Lack of Candida treatment coverage and, if present, antifungal resistance may result in VDS treatment failure. This study aimed to determine the prevalence of Candida infection, antifungal resistance, and coinfections in Namibian women with VDS.

METHODS

A cross-sectional study was performed using 253 vaginal swabs from women with VDS in Namibia. Demographic data was collected, and phenotypic and molecular detection of Candida species was performed followed by fluconazole susceptibility testing of Candida isolates. BV was diagnosed using Nugent score microscopy; molecular detection of Chlamydia trachomatis, Neisseria gonorrhoeae and Trichomonas vaginalis was performed.

RESULTS

Candida species was detected in 110/253 women (43%). Ninety women (36%) had Candida albicans and 24 (9.5%) had non-albicans Candida species. The non-albicans species detected were 19 (17%) Candida glabrata, 4.0 (3.5%) Candida krusei, and 1.0 (0.9%) Candida parapsilosis. Candida albicans were more frequently isolated in younger (p = 0.004) and pregnant women (p = 0.04) compared to non-albicans Candida species. Almost all (98%) Candida albicans isolates were susceptible to fluconazole while all non-albicans Candida species were fluconazole resistant. STIs were diagnosed in 92 women (36%): 30 (12%) with C. trachomatis, 11 (4.3%) N. gonorrhoeae, and 70 (28%) T. vaginalis; 98 (39%) women had BV. Candida infection alone was diagnosed in 30 women (12%), combined with STIs in 42 women (17%) and was concurrent with BV in 38 women (15%). Candida infection was more often detected in swabs from women without C. trachomatis detected (6.4% vs. 16%; OR 0.30; 95% CI 0.10-0.77, p = 0.006).

CONCLUSIONS

The high prevalence of Candida infection, especially those due to non-albicans Candida species that are resistant to fluconazole, is a great concern in our setting and may lead to poor treatment outcomes. Access to microbiological testing for Candida species in the context of syndromic management is warranted.

Comparative Analysis of Epidemiological and Clinical Characteristics Between Invasive Candida Infection versus Colonization in Critically Ill Patients in a Tertiary Hospital in Anhui, China

Objective

Invasive infections due to Candida spp. have unique epidemiology, strain distribution, antimicrobial susceptibility, and clinical features. This study aimed to compare and evaluate these characteristic variables between invasive Candida infection and colonization of critically ill patients in local China to potentially improve differential diagnosis and therapy.

Methods

A total of 193 critically ill patients were recruited and followed up for the study, and 133 Candida isolates were obtained from invasive Candida-infected or -colonized subjects. The strains were identified to species level through matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry, assisted by DNA sequencing. Candida susceptibility to common antifungals, including azoles, was determined by microbroth ATB Fungus 3 methodology. Azole resistance–related gene sequencing and homologous 3D-structure modeling were employed. Patient demographics and clinical risk factors were documented and comparatively analyzed from the hospital information-management system.

Results

Non–C. albicans Candida (56%) principally caused invasive Candida infections, while C. albicans (55.17%) contributed more to Candida colonization in critically ill patients. Additional risk factors exerted significant impact on both Candida cohorts, primarily including invasive interventions, cancers, and concurrent infections in common. Most colonized Candida spp. harbored relatively higher sensitivity to azoles. ERG11 gene mutations of T348A and A1309G, A395T and C461T, and a novel G1193T to our knowledge were identified in azole-resistant C. albicans, C. tropicalis, and C. parapsilosis respectively, and their corresponding homologous 3D-structure modeling was putatively achieved.

Conclusion

Distinct epidemiological and clinical characteristics existed between invasive Candida infection and colonization in critically ill patients. Multiple risk factors significantly involved both the Candida cohorts. Colonized Candida exhibited generally higher azole sensitivity than invasively infectious counterparts. ERG11 point mutations had mechanistically potential ties with local Candida resistance to azoles.

Petrositis caused by fluconazole-resistant candida: case report and literature review

Background

Petrositis is a rare and fatal complication associated with otitis media. It is most likely caused by bacterial infections, but in some cases it is caused by fungal infections.

Case study

The case in this report is associated with fungal petrositis. The clinical symptoms are: ear pain from chronic otitis media, severe headache, peripheral facial palsy and diplopia. The case was finally confirmed through imaging of middle ear, bacterial culture, pathology, and blood Metagenomic next-generation sequencing (mNGS) test. The patient was treated with sensitive antifungal drugs.

Conclusion

Drug treatment is conservative but efficient method in this case. mNGS can provide pathogenic reference, when antibiotic is not efficient enough for fungal infections or drug-resistant fungal infections cases. This allows we to adjust drug use for the treatment.

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.

Immunosuppressed Patients with Clinically Diagnosed Invasive Fungal Infections: The Fungal Species Distribution, Antifungal Sensitivity and Associated Risk Factors in a Tertiary Hospital of Anhui Province

Objective

Since the nosocomial fungal infections increasingly emerge, we extensively investigated the fungal species stratification and antifungal sensitivity profiles, clinical characteristics and associated risk factors of immunosuppressed patients with clinically diagnosed invasive fungal infections (IFIs) in a tertiary hospital of Anhui province.

Methods

In total, 112 subjects with immunosuppressive state were enrolled from a comprehensive tertiary hospital in Central China between July 2019 and December 2021. Eight-one fungal isolates were clinically recovered by fungus-culturing approaches. The identifications were conducted through a mass spectrometry detecting platform. The susceptibilities to antifungals were tested using the broth micro-dilution method, and the possible antifungal azole-resistance mechanism in specific Candida species was availably explored by sequencing. Patient medical profiles were accessed via the digitized retrieval system of hospital, from which clinical outcomes and multiple risk factors for immunosuppressed patients with clinically diagnosed IFIs were explicitly documented for evaluation.

Results

Candida species predominated in clinically diagnosed IFIs of immunosuppressed patients (accounting for 88.88%), followed by Trichosporon and Aspergillus species (6.17% and 4.94%, respectively). The source types of specimen were primarily comprised of urine (41.98%), respiratory samples (33.33%) and peripheral blood (9.88%). Frequently isolated Candida and Trichosporon species exhibited a high level of in vitro sensitivity for amphotericin B and 5-fluorocytosine, whereas a substantial portion of Candida species including C. glabrata, C. parapsilosis complex and C. tropicalis, and Trichosporon species showed lowered sensitivity patterns toward itraconazole, fluconazole and voriconazole at different levels. Specifically, gene mutations of ERG11 were identified in azole-resistant C. tropicalis. Distinct risk factors were analyzed to be highly associated with the clinically diagnosed IFI incidence, mainly including hospitalization duration, surgical procedures, immunosuppressive treatments, underlying diseases and other conditions.

Conclusion

Candida, Trichosporon and Aspergillus species were the top three pathogenic fungal agents causing clinically diagnosed IFIs in immunosuppressed patients. The attenuated sensitivity to azoles in Candida and Trichosporon species needs close surveillance, and ERG11 polymorphism might contribute to azole resistance in specific Candida species. Multiple featured risk factors for immunosuppressed patients developing clinically diagnosed IFIs require further consideration during clinical practice.

Characterisation of Candida parapsilosis CYP51 as a Drug Target Using Saccharomyces cerevisiae as Host

The fungal cytochrome P450 lanosterol 14α-demethylase (CYP51) is required for the biosynthesis of fungal-specific ergosterol and is the target of azole antifungal drugs. Despite proven success as a clinical target for azole antifungals, there is an urgent need to develop next-generation antifungals that target CYP51 to overcome the resistance of pathogenic fungi to existing azole drugs, toxic adverse reactions and drug interactions due to human drug-metabolizing CYPs. Candida parapsilosis is a readily transmitted opportunistic fungal pathogen that causes candidiasis in health care environments. In this study, we have characterised wild type C. parapsilosis CYP51 and its clinically significant, resistance-causing point mutation Y132F by expressing these enzymes in a Saccharomyces cerevisiae host system. In some cases, the enzymes were co-expressed with their cognate NADPH-cytochrome P450 reductase (CPR). Constitutive expression of CpCYP51 Y132F conferred a 10- to 12-fold resistance to fluconazole and voriconazole, reduced to ~6-fold resistance for the tetrazoles VT-1161 and VT-1129, but did not confer resistance to the long-tailed triazoles. Susceptibilities were unchanged in the case of CpCPR co-expression. Type II binding spectra showed tight triazole and tetrazole binding by affinity-purified recombinant CpCYP51. We report the X-ray crystal structure of ScCYP51 in complex with VT-1129 obtained at a resolution of 2.1 Å. Structural analysis of azole—enzyme interactions and functional studies of recombinant CYP51 from C. parapsilosis have improved understanding of their susceptibility to azole drugs and will help advance structure-directed antifungal discovery.

OUP accepted manuscript

The increasing incidence and changing epidemiology of invasive fungal infections continue to present many challenges to their effective management. The repertoire of antifungal drugs available for treatment is still limited although there are new antifungals on the horizon. Successful treatment of invasive mycoses is dependent on a mix of pathogen-, host- and antifungal drug-related factors. Laboratories need to be adept at detection of fungal pathogens in clinical samples in order to effectively guide treatment by identifying isolates with acquired drug resistance. While there are international guidelines on how to conduct in vitro antifungal susceptibility testing, these are not performed as widely as for bacterial pathogens. Furthermore, fungi generally are recovered in cultures more slowly than bacteria, and often cannot be cultured in the laboratory. Therefore, non-culture-based methods, including molecular tests, to detect fungi in clinical specimens are increasingly important in patient management and are becoming more reliable as technology improves. Molecular methods can also be used for detection of target gene mutations or other mechanisms that predict antifungal drug resistance. This review addresses acquired antifungal drug resistance in the principal human fungal pathogens and describes known resistance mechanisms and what in-house and commercial tools are available for their detection. It is emphasized that this approach should be complementary to culture-based susceptibility testing, given the range of mutations, resistance mechanisms and target genes that may be present in clinical isolates, but may not be included in current molecular assays.

Recent Molecular Tools for the Genetic Manipulation of Highly Industrially Important Mucoromycota Fungi

Mucorales is the largest and most well-studied order of the phylum Mucormycota and is known for its rapid growth rate and various industrial applications. The Mucorales fungi are a fascinating group of filamentous organisms with many uses in research and the industrial and medical fields. They are widely used biotechnological producers of various secondary metabolites and other value-added products. Certain members of Mucorales are extensively used as model organisms for genetic and molecular investigation and have extended our understanding of the metabolisms of other members of this order as well. Compared with other fungal species, our understanding of Mucoralean fungi is still in its infancy, which could be linked to their lack of effective genetic tools. However, recent advancements in molecular tools and approaches, such as the construction of recyclable markers, silencing vectors, and the CRISPR-Cas9-based gene-editing system, have helped us to modify the genomes of these model organisms. Multiple genetic modifications have been shown to generate valuable products on a large scale and helped us to understand the morphogenesis, basic biology, pathogenesis, and host–pathogen interactions of Mucoralean fungi. In this review, we discuss various conventional and modern genetic tools and approaches used for efficient gene modification in industrially important members of Mucorales.

HPLC-MS identification and expression of Candida drug-resistance proteins from African HIV-infected patients

The objective of this study was to elucidate the proteomic mechanisms of drug resistance in HIV-infected African patients. Cell membrane fractions from forty oral Candida isolates isolated from African HIV-positive patients were analysed using HPLC-MS with the aim of identifying proteins associated with their pathogenicity and drug resistance. Heat shock proteins that mediate the fungicidal activity of salivary peptides were found in all tested Candida fractions, with pH-responsive proteins associated with increased pathogenicity only being present in the three most commonly isolated species. ABC multidrug transporter efflux pumps and estrogen binding proteins were only found in C. albicans fractions, while ergosterol biosynthesis proteins were identified in four species. The combination of various adherence, invasion, upregulation and efflux pump mechanisms appear to be instrumental for the Candida host colonization and drug resistance emergence in HIV-infected individuals.

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.

Mechanisms of Azole Resistance and Trailing in Candida tropicalis Bloodstream Isolates

Objectives: Azole-resistant Candida tropicalis has emerged in Asia in the context of its trailing nature, defined by residual growth above minimum inhibitory concentrations (MICs). However, limited investigations in C. tropicalis have focused on the difference of genotypes and molecular mechanisms between these two traits. Methods: Sixty-four non-duplicated C. tropicalis bloodstream isolates collected in 2017 were evaluated for azole MICs by the EUCAST E.def 7.3.1 method, diploid sequence type (DST) by multilocus sequencing typing, and sequences and expression levels of genes encoding ERG11, its transcription factor, UPC2, and efflux pumps (CDR1, CDR2 and MDR1). Results: Isavuconazole showed the highest in vitro activity and trailing against C. tropicalis, followed by voriconazole and fluconazole (geometric mean [GM] MIC, 0.008, 0.090, 1.163 mg/L, respectively; trailing GM, 27.4%, 20.8% and 19.5%, respectively; both overall p < 0.001). Fourteen (21.9%) isolates were non-WT to fluconazole/voriconazole, 12 of which were non-WT to isavuconazole and clustered in clonal complex (CC) 3. Twenty-five (39.1%) isolates were high trailing WT, including all CC2 isolates (44.0%) (containing DST140 and DST98). All azole non-WT isolates carried the ERG11 mutations A395T/W and/or C461T/Y, and most carried the UPC2 mutation T503C/Y. These mutations were not identified in low and high trailing WT isolates. Azole non-WT and high trailing WT isolates exhibited the highest expression levels of ERG11 and MDR1, 3.91- and 2.30-fold, respectively (both overall p < 0.01). Conclusions: Azole resistance and trailing are phenotypically and genotypically different in C. tropicalis. Interference with azole binding and MDR1 up-regulation confer azole resistance and trailing, respectively.

Update on Candida krusei, a potential multidrug-resistant pathogen

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

Antimycotic Drugs and their Mechanisms of Resistance to Candida Species

Fungal infections have shown an upsurge in recent decades, which is mainly because of the increasing number of immunocompromised patients and the occurrence of invasive candidiasis has been found to be 7-15 fold greater than that of invasive aspergillosis. The genus Candida comprises more than 150 distinct species, however, only a few of them are found to be pathogenic to humans. Mortality rates of Candida species are found to be around 45% and the reasons for this intensified mortality are inefficient diagnostic techniques and unfitting initial treatment strategies. There are only a few antifungal drug classes that are employed for the remedy of invasive fungal infections. which include azoles, polyenes, echinocandins, and pyrimidine analogs. During the last 2-3 decades, the usage of antifungal drugs has increased several folds due to which the reports of escalating antifungal drug resistance have also been recorded. The resistance is mostly to the triazole- based compounds. Due to the occurrence of antifungal drug resistance, the success rates of treatment have been reduced as well as major changes have been observed in the frequency of fungal infections. In this review, we have summarized the major molecular mechanisms for the development of antifungal drug resistance.

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.

Azole resistance in Candida from animals calls for the One Health approach to tackle the emergence of antimicrobial resistance

This study initially aimed at investigating the occurrence of azole resistance among Candida spp. from animals and analyzing the involvement of efflux pumps in the resistance phenomenon. Then, the dynamics of antifungal resistance was assessed, by comparing the antifungal epidemiological cutoff values (ECVs) against C. albicans and C. tropicalis from humans and animals. Fifty azole-resistant isolates (24 C. albicans, 24 C. tropicalis; 2 C. parapsilosis sensu lato) were submitted to the efflux pump inhibition assay with promethazine and significant MIC reductions were observed for fluconazole (2 to 250-fold) and itraconazole (16 to 4000-fold). Then, the antifungal ECVs against C. albicans and C. tropicalis from human and animal isolates were compared. Fluconazole, itraconazole and voriconazole ECVs against human isolates were lower than those against animal isolates. Based on the antifungal ECVs against human isolates, only 33.73%, 50.39% and 63.53% of C. albicans and 52.23%, 61.85% and 55.17% of C. tropicalis from animals were classified as wild-type for fluconazole, itraconazole and voriconazole, respectively. Therefore, efflux-mediated mechanisms are involved in azole resistance among Candida spp. from animals and this phenomenon seems to emerge in animal-associated niches, pointing to the existence of environmental drivers of resistance and highlighting the importance of the One Health approach to control it.

Lanosterol 14α-demethylase (CYP51)/histone deacetylase (HDAC) dual inhibitors for treatment of Candida tropicalis and Cryptococcus neoformans infections

Invasive fungal infections remain a challenge due to lack of effective antifungal agents and serious drug resistance. Discovery of antifungal agents with novel antifungal mechanism is important and urgent. Previously, we designed the first CYP51/HDAC dual inhibitors with potent activity against resistant Candida albicans infections. To better understand the antifungal spectrum and synergistic mechanism, herein new CYP51/HDAC dual inhibitors were designed which showed potent in vitro and in vivo antifungal activity against C. neoformans and C. tropicalis infections. Antifungal mechanism studies revealed that the CYP51/HDAC dual inhibitors acted by inhibiting various virulence factors of C. tropicalis and C. neoformans and down-regulating resistance-associated genes. This study highlights the potential of CYP51/HDAC dual inhibitors as a promising strategy for the discovery of novel broad-spectrum antifungal agents.

The relationship between biofilm formation and mortality in patients with Candida tropicalis candidemia

BACKGROUND

Biofilm formation by Candida species is an influential virulence factor in candidemia pathogenesis. We investigated the relationship between biofilm formation of Candida tropicalis isolates with the clinical characteristics and mortality outcomes in patients with candidemia.

MATERIALS AND METHODS

Thirty-nine C. tropicalis isolates were recovered from patients with candidemia admitted to two university hospitals in Tehran, Iran. Biofilm mass and metabolic activity of C. tropicalis biofilms were assessed in vitro with two colorimetric methods. The sessile minimum inhibitory concentrations (SMICs) were evaluated in vitro by treating preformed biofilms with diluted concentrations of azoles according to CLSI-M27 A3/S4 protocol, followed by metabolic activity quantification. The expressions of ERG11, UPC2, MDR1, and CDR1 genes were also evaluated.

RESULTS

All C. tropicalis isolates produced biofilm. Respectively, higher <7-day and ≥7-day mortality rates were found among cases with high metabolic activity (46.7% vs. 13%, P = 0.03) and high biofilm mass (31.8% vs. 0, P = 0.029). Sessile cells had high resistance to fluconazole, voriconazole, and itraconazole. The azole minimum inhibitory concentrations (MICs) of C. tropicalis sessile were significantly greater than the planktonic minimum inhibitory concentrations (PMICs). In fluconazole-treated biofilms, the expression of ERG11 and UPC2 genes was increased.

CONCLUSION

Our findings highlight the importance of C. tropicalis biofilm formation as an important factor in candidemia pathogenesis and the clinical outcome of patients with candidemia.

Recent Advances in Genome Editing Tools in Medical Mycology Research

Manipulating fungal genomes is an important tool to understand the function of target genes, pathobiology of fungal infections, virulence potential, and pathogenicity of medically important fungi, and to develop novel diagnostics and therapeutic targets. Here, we provide an overview of recent advances in genetic manipulation techniques used in the field of medical mycology. Fungi use several strategies to cope with stress and adapt themselves against environmental effectors. For instance, mutations in the 14 alpha-demethylase gene may result in azole resistance in Aspergillusfumigatus strains and shield them against fungicide's effects. Over the past few decades, several genome editing methods have been introduced for genetic manipulations in pathogenic fungi. Application of restriction enzymes to target and cut a double-stranded DNA in a pre-defined sequence was the first technique used for cloning in Aspergillus and Candida. Genome editing technologies, including zinc-finger nucleases (ZFNs) and transcriptional activator-like effector nucleases (TALENs), have been also used to engineer a double-stranded DNA molecule. As a result, TALENs were considered more practical to identify single nucleotide polymorphisms. Recently, Class 2 type II Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/Cas9 technology has emerged as a more useful tool for genome manipulation in fungal research.

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.

Emergence of clonal fluconazole-resistant Candida parapsilosis clinical isolates in a multicentre laboratory-based surveillance study in India

OBJECTIVES

The emergence of fluconazole resistance in Candida parapsilosis healthcare-associated infections has recently been increasingly reported. Antifungal susceptibility profiles and mechanisms of fluconazole resistance in C. parapsilosis (n = 199) from nine hospitals in India collected over a period of 3 years were studied. Further, clonal transmission of fluconazole-resistant isolates in different hospitals was investigated.

METHODS

Antifungal susceptibility testing of five azoles, amphotericin B and 5-flucytosine was performed by the CLSI microbroth dilution method. The azole target ERG11 gene was sequenced, and the significance of a novel ERG11 mutation in C. parapsilosis was determined using a gap-repair cloning approach in Saccharomyces cerevisiae. In addition, microsatellite analysis was performed to determine the clonal lineage of C. parapsilosis-resistant strains circulating among different hospitals.

RESULTS

A total of 64 (32%) C. parapsilosis isolates were non-susceptible to fluconazole, which included resistant (n = 55; MIC >4 mg/L) and susceptible dose-dependent (n = 9) isolates. Of these 64 non-susceptible isolates, a novel K143R amino acid substitution was noted in 92%, and the remaining five isolates had the Y132F substitution. Elevated azole MICs (≥16-fold) were detected in S. cerevisiae upon expression of C. parapsilosis ERG11 alleles carrying Y132F or K143R substitutions. Two major clusters of non-susceptible isolates were circulating in seven Indian hospitals.

CONCLUSIONS

We report a novel K143R amino acid substitution in ERG11p causing fluconazole resistance in C. parapsilosis. Fluconazole-non-susceptible C. parapsilosis isolates carrying the novel K143R amino acid substitution should be identified in clinical microbiology laboratories to prevent further clonal transmission.

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.

Detection of ERG11 Overexpression in Candida albicans isolates from environmental sources and clinical isolates treated with inhibitory and subinhibitory concentrations of fluconazole

BACKGROUND

Candida species can cause serious infection in patients with changes in defence mechanisms and/or when anatomical barriers are compromised. Mutations and overexpression in the ERG11 gene are described as molecular mechanisms of azole resistance. Information is limited on these mechanisms in the presence of subinhibitory concentrations of fluconazole.

OBJECTIVES

This study aimed to evaluate the expression of ERG11 gene from Candida albicans isolates, from clinical and hospital environments, in the absence and presence of inhibitory and subinhibitory concentrations of fluconazole.

METHODS

The American Type Culture Collection 10231 strain, five clinical isolates and three isolates from hospital environment colonisation were exposed to inhibitory and subinhibitory concentrations of fluconazole. Susceptibility tests were performed according to EUCAST 7.1 guidelines, and the relative expression analysis of ERG11 was performed by qPCR.

RESULTS

Differences in response to fluconazole concentrations were observed, with the exception only one clinical isolate when treated with 1/4 of the FLU-minimum inhibitory concentration (MIC). All the other isolates, regardless of the isolation source, had an increase in expression. The overexpression occurred in a very broad range, from 1.086 to 126.105 times. In general, treatment with the highest dose of fluconazole (MIC) was the one that most influenced the ERG11 expression, followed by treatments with 1/2 and 1/4 MIC.

CONCLUSIONS

The increased expression of ERG11 by C albicans in the presence of different concentrations of fluconazole is relevant, raising concerns in the care and cleaning of the hospital environment and the prophylactic use of fluconazole that could lead to the selection of potential azole-resistant isolates.

Antifungal Susceptibility of Non-albicans Candida Species in A Tertiary Care Hospital, Bulgaria

Background: Emerging non-albicans Candida (NAC) species are a major threat because of their intrinsic or acquired resistance to routinely applied antifungal agents. Objectives: The purpose of our study was to reveal in vitro activity of nine antifungal agents against NAC isolates. Methods: A total of 67 NAC (27 Candida glabrata, 10 C. tropicalis, 6 C. krusei, 6 C. parapsilosis, 4 C. lusitaniae, 4 C. lipolytica, etc.) were identified and tested. The antifungal susceptibility was estimated on the basis of minimum inhibitory concentrations (MIC). Results: Overall, 13 species were determined, of which C. glabrata was the most common (40.3%), followed by C. tropicalis (14.9%), C. krusei, and C. parapsilosis (8.9 % each). Forty-nine NAC isolates (73.13%) demonstrated decreased susceptibility to one or more antifungals, and 18 of them were resistant to all azoles. Out of 27 C. glabrata, 12 (44.4%) were resistant to fluconazole with MICs: 32 - >128 µg/mL and 15 (55.6%) were intermediate with MICs: 8 - 16 µg/mL Non-albicans Candida revealed a good susceptibility to echinocandins. Amphotericin B resistance was found in 5.97% of the isolates. Of particular interest was the detection of 6 (8.95%) multidrug-resistant NAC, which expressed resistance to azoles and echinocandins and/or amphotericin B. Conclusions: About one-fourth of the studied NAC were resistant to all azoles. These findings as well as the detection of several multidrug-resistant isolates determine the necessity of susceptibility testing of clinically important yeast isolates and control of the antifungal drugs in our hospital.

The use of nanoparticles as alternative therapeutic agents against Candida infections: an up-to-date overview and future perspectives

Candida spp. are opportunistic fungi that can cause severe infections especially in immunocompromised patients. Candidiasis is currently the most frequent fungal disease affecting humans globally. This rise is attributed to the vast increase in resistance to antifungal agents. In recent years, the epidemiological and clinical relevance of fungal infections caused by Candida species have attracted a lot of interest with increasing reports of intrinsic and acquired resistance among Candida species. Thus, the formulation of novel, and efficient therapy for Candida infection persists as a critical challenge in modern medicine. The use of nanoparticle as a potential biomaterial to achieve this feat has gained global attention. Nanoparticles have shown promising antifungal activity, and thus, could be seen as the next generation antifungal agents. This review concisely discussed Candida infection with emphasis on anti-candida resistance mechanisms and the use of nanoparticles as potential therapeutic agents against Candida species. Moreover, the mechanisms of activity of nanoparticles against Candida species, recent findings on the anti-candida potentials of nanoparticles and future perspectives are also presented.

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.

Antifungal Activity and Potential Mechanism of Panobinostat in Combination With Fluconazole Against Candida albicans

Invasive fungal infections are an emerging problem worldwide, which bring huge health challenges. Candida albicans, the most common opportunistic fungal pathogen, can cause bloodstream infections with high mortality in susceptible hosts. At present, available antifungal agents used in clinical practice are limited, and most of them also have some serious adverse effects. The emergence of drug resistance because of the wide use of antifungal agents is a new limitation to successful patient therapy. Drug combination therapy is increasingly becoming a way to enhance antifungal efficacy, and reduce drug resistance and potential toxicity. Panobinostat, as a pan-histone deacetylase inhibitor, has been approved by the United States Food and Drug Administration as novel antitumor agents. In this study, the antifungal effects and mechanisms of panobinostat combined with fluconazole (FLC) against C. albicans were explored for the first time. The results indicated that panobinostat could work synergistically with FLC against resistant C. albicans, the minimal inhibitory concentration (MIC) of panobinostat could decrease from 128 to 0.5–2 μg/ml and the MIC of FLC could decrease from >512 to 0.25–0.5 μg/ml, and the fractional inhibitory concentration index (FICI) value ranged from 0.0024 to 0.0166. It was not only synergized against planktonic cells but also against C. albicans biofilms performed ≤8 h when panobinostat is combined with fluconazole; the sessile MIC (sMIC) of panobinostat could decrease from >128 to 0.5–8 μg/ml and the sMIC of FLC from >1024 to 0.5–2 μg/ml, and the FICI value was <0.5. The Galleria mellonella infection model was used to evaluate the in vivo effect of the drug combination, and the result showed that the survival rate could be improved obviously. Finally, we explored the synergistic mechanisms of the drug combination. The hyphal growth, which plays roles in drug resistance, was found to be inhibited, and metacaspase which is related to cell apoptosis was activated (p < 0.01), whereas the synergistic effects were proven not to be related to the efflux pumps (p > 0.05). These findings might provide novel insights into the antifungal drug discovery and the treatment of candidiasis caused by C. albicans.

Modulation of ERG Genes Expression in Clinical Isolates of Candida tropicalis Susceptible and Resistant to Fluconazole and Itraconazole

Candida tropicalis is a non-albicans Candida specie that causes candidosis in several countries, including Brazil. However, little is known about the mechanisms of drug resistance in C. tropicalis infections. In this study, we used clinical isolates of C. tropicalis susceptible as well as resistant to either Fluconazole or Itraconazole to assess the relationship between drug resistance and the expression of ERG and efflux pump genes. Our results showed that the main mechanism of resistance against both Fluconazole and Itraconazole in this specie is through the up-regulation of ERG rather than that of the efflux pump genes. We demonstrated that, although pre-treatment with azole drugs increases the expression of both ERG6 and ERG11 genes, the resistant or susceptible dose-dependent (SDD) samples are able to maintain high expression levels of these genes for longer periods of time than the susceptible samples.

Potential of Methylglyoxal-Conjugated Chitosan Nanoparticles in Treatment of Fluconazole-Resistant Candida albicans Infection in a Murine Model

Background

Fungal infections are becoming more prevalent and threatening because of the continuous emergence of azole-resistant fungal infections. The present study was aimed to assess the activity of free Methylglyoxal (MG) or MG-conjugated chitosan nanoparticles (MGCN) against fluconazole-resistant Candida albicans.

Materials and Methods

A novel formulation of MGCN was prepared and characterized to determine their size, shape and polydispersity index. Moreover, the efficacy of fluconazole or MG or MGCN was determined against intracellular C. albicans in macrophages and the systematic candidiasis in a murine model. The safety of MG or MGCN was tested in mice by analyzing the levels of hepatic and renal toxicity parameters.

Results

Candida albicans did not respond to fluconazole, even at the highest dose of 20 mg/kg, whereas MG and MGCN effectively eliminated C. albicans from the macrophages and infected mice. Mice in the group treated with MGCN at a dose of 10 mg/kg exhibited a 90% survival rate and showed the lowest fungal load in the kidney, whereas the mice treated with free MG at the same dose exhibited 50% survival rate. Moreover, the administration of MG or MGCN did not induce any liver and kidney toxicity in the treated mice.

Conclusion

The findings of the present work suggest that MGCN may be proved a promising therapeutic formulation to treat azole-resistant C. albicans infections.

The effect of Ginkgolide B combined with fluconazole against drug-resistant Candida albicans based on common resistance mechanisms

The number of invasive fungal infections has increased dramatically over recent years, leading to high morbidity and mortality of immunocompromised patients. Candida albicans is the most common cause of life-threatening disseminated candidiasis among invasive fungal infections. Resistance of C. albicans against conventional antifungals is frequently reported. Treatment with a combination of antifungal and non-antifungal agents is often considered in the aim to overcome drug resistance. This study shows for the first time that the combination of ginkgolide B (GB) and fluconazole (FLC) increases the sensitivity of resistant C. albicans to FLC. In vitro studies indicated that the drug combination had a synergistic effect on C. albicans in both planktonic cells and biofilms within 12 h. In vivo efficacy of this drug combination was evaluated using the Galleria mellonella infection model. Survival rate, fungal burden, and histological examination were determined. Studies indicated that the antifungal effects of GB in combination with FLC might be associated with inhibition of hyphal growth, disruption of intracellular calcium, and inhibition of drug efflux pumps. The results indicate a promising solution for overcoming drug resistance of C. albicans and expanding the clinical application of existing drugs.

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.