CoERG11 A395T mutation confers azole resistance in Candida orthopsilosis clinical isolates

Precise genome editing underlines the distinct contributions of mutations in ERG11, ERG3, MRR1, and TAC1 genes to antifungal resistance in Candida parapsilosis

Candida parapsilosis has recently emerged as a major threat due to the worldwide emergence of fluconazole-resistant strains causing clonal outbreaks in hospitals and poses a therapeutic challenge due to the limited antifungal armamentarium. Here, we used precise genome editing using CRISPR-Cas9 to gain further insights into the contribution of mutations in ERG11, ERG3, MRR1, and TAC1 genes and the influence of allelic dosage to antifungal resistance in C. parapsilosis. Seven of the most common amino acid substitutions previously reported in fluconazole-resistant clinical isolates (including Y132F in ERG11) were engineered in two fluconazole-susceptible C. parapsilosis lineages (ATCC 22019 and STZ5). Each mutant was then challenged in vitro against a large array of antifungals, with a focus on azoles. Any possible change in virulence was also assessed in a Galleria mellonella model. We successfully generated a total of 19 different mutants, using CRISPR-Cas9. Except for R398I (ERG11), all remaining amino acid substitutions conferred reduced susceptibility to fluconazole. However, the impact on fluconazole in vitro susceptibility varied greatly according to the engineered mutation, the stronger impact being noted for G583R acting as a gain-of-function mutation in MRR1. Cross-resistance with newer azoles, non-medical azoles, but also non-azole antifungals such as flucytosine, was occasionally noted. Posaconazole and isavuconazole remained the most active in vitro. Except for G583R, no fitness cost was associated with the acquisition of fluconazole resistance. We highlight the distinct contributions of amino acid substitutions in ERG11, ERG3, MRR1, and TAC1 genes to antifungal resistance in C. parapsilosis.

Candida parapsilosis complex in the clinical setting

Representatives of the Candida parapsilosis complex are important yeast species causing human infections, including candidaemia as one of the leading diseases. This complex comprises C. parapsilosis, Candida orthopsilosis and Candida metapsilosis, and causes a wide range of clinical presentations from colonization to superficial and disseminated infections with a high prevalence in preterm-born infants and the potential to cause outbreaks in hospital settings. Compared with other Candida species, the C. parapsilosis complex shows high minimal inhibitory concentrations for echinocandin drugs due to a naturally occurring FKS1 polymorphism. The emergence of clonal outbreaks of strains with resistance to commonly used antifungals, such as fluconazole, is causing concern. In this Review, we present the latest medical data covering epidemiology, diagnosis, resistance and current treatment approaches for the C. parapsilosis complex. We describe its main clinical manifestations in adults and children and highlight new treatment options. We compare the three sister species, examining key elements of microbiology and clinical characteristics, including the population at risk, disease manifestation and colonization status. Finally, we provide a comprehensive resource for clinicians and researchers focusing on Candida species infections and the C. parapsilosis complex, aiming to bridge the emerging translational knowledge and future therapeutic challenges associated with this human pathogen.

Antifungal Resistance and Genotyping of Clinical Candida parapsilosis Complex in Japan

Non-albicans Candida infections have recently gained worldwide attention due to their intrinsic resistance to different antifungal agents and the limited therapeutic options for treating them. Although the Candida parapsilosis complex is reported to be the second or third most prevalent Candida spp., little information is available on the prevalence of antifungal resistance along with genotyping of the C. parapsilosis complex. In this study, we aimed to evaluate the prevalence of antifungal resistance, the genetic basis of such resistance, and the genotyping of C. parapsilosis complex isolates that were recovered from hospitalized patients in Japan from 2005 to 2019. Our results indicated that, with the exception of one single C. metapsilosis isolate that was dose-dependently susceptible to fluconazole, all other isolates were susceptible or showed wild phenotypes to all tested antifungals, including azoles, echinocandins, amphotericin B, and flucytosine. Molecular analyses for azole and echinocandin resistance via evaluating ERG11 mutation and FKS1 hotspot one (HS1) and hotspot two (HS2) mutations, respectively, confirmed the phenotypic results. Genotyping of our isolates confirmed that they belong to 53 different but closely related genotypes, with a similarity percentage of up to 90%. Our results are of significant concern, since understanding the genetic basis of echinocandin resistance in the C. parapsilosis complex as well their genotyping is essential for directing targeted therapy, identifying probable infection sources, and developing strategies for overcoming epidemic spread.

Paradigm Shift: Candida parapsilosis sensu stricto as the Most Prevalent Candida Species Isolated from Bloodstream Infections with Increasing Azole-Non-Susceptibility Rates: Trends from 2015-2022 Survey

Candidemia is the fourth most common healthcare-related bloodstream infection. In recent years, incidence rates of Candida parapsilosis have been on the rise, with differences in prevalence and antifungal susceptibility between countries. The aim of the present study was to evaluate temporal changes in prevalence and antifungal susceptibility of C. parapsilosis among other species causing candidemia. All candidemia episodes from January 2015 to August 2022 were evaluated in order to depict time trends in prevalence of C. parapsilosis sensu stricto among all Candida species recovered from blood cultures as well as fluconazole- and voriconazole-non-susceptibility rates. Secondary analyses evaluated time trends in prevalence and antifungal non-susceptibility according to clinical settings. The overall prevalence of C. parapsilosis was observed to increase compared to the prevalence of other Candida species over time (p-trend = 0.0124). From 2019, the number of C. parapsilosis sensu stricto isolates surpassed C. albicans, without an increase in incidence rates. Overall rates of fluconazole- and voriconazole-non-susceptible C. parapsilosis sensu stricto were both 3/44 (6.8%) in 2015 and were 32/51 (62.7%) and 27/51 (52.9%), respectively, in 2022 (85% cross-non-susceptibility). The risk of detecting fluconazole- or voriconazole-non-susceptibility was found to be higher in C. parapsilosis compared to other Candida species (odds ratio (OR) = 1.60, 95% CI [1.170, 2.188], p-value < 0.0001 and OR = 12.867, 95% CI [6.934, 23.878], p-value < 0.0001, respectively). This is the first study to report C. parapsilosis sensu stricto as the most prevalent among Candida spp. isolated from blood cultures, with worrisome fluconazole- and voriconazole-non-susceptibility rates, unparalleled among European and North American geographical regions.

Candida parapsilosis sensu stricto Antifungal Resistance Mechanisms and Associated Epidemiology

Fungal diseases cause millions of deaths per year worldwide. Antifungal resistance has become a matter of great concern in public health. In recent years rates of non-albicans species have risen dramatically. Candida parapsilosis is now reported to be the second most frequent species causing candidemia in several countries in Europe, Latin America, South Africa and Asia. Rates of acquired azole resistance are reaching a worrisome threshold from multiple reports as in vitro susceptibility testing is now starting also to explore tolerance and heteroresistance to antifungal compounds. With this review, the authors seek to evaluate known antifungal resistance mechanisms and their worldwide distribution in Candida species infections with a specific focus on C. parapsilosis.

cleanSURFACES® intervention reduces microbial activity on surfaces in a senior care facility

As one of the top public health challenges outlined by the Centers for Disease Control (CDC), estimates report that hospital acquired infections (HAIs) claim the lives of 99,000 Americans and cost healthcare providers over $28 billion each year. In addition to underlying conditions related to age, elderly patients in long-term care facilities are at an elevated risk of acquiring HAIs. A large percentage of HAIs is attributable to contaminated surfaces and medical devices. To that end, this study utilized a metatranscriptomic sequencing workflow (CSI-Dx™) to profile active microbial communities from surfaces in the HJ Heinz Community Living Center, a long-term care facility in the Veterans Affairs Pittsburgh Health Care System. Swabs were collected from high-touch surfaces (Keyboard, Ledge, Workstation on Wheels, Worksurfaces) before (Baseline) and after cleanSURFACES^® were installed at 4 timepoints (Day 1, Day 7, Day 14, and Day 30). Microbial richness was significantly reduced after cleanSURFACES^® intervention (Wilcoxon test with Holm correction, p=0.000179). Beta diversity results revealed distinct clustering between Baseline and Post-intervention samples (Adonis, p<0.001). Reduction in bacterial (Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis) and fungal (Malassezia restricta, Candida albicans, Candida glabrata, and Candida orthopsilosis) expression of opportunistic pathogens was observed. Additionally, a subset of taxa (Corynebacterium, Cutibacterium acnes, and Ralstonia pickettii) was present in specific Post-intervention timepoints and surface types. This study revealed decreased microbial activity, highlighting the potential for the combinatorial application of cleanSURFACES^® and regular decontamination practices to reduce the prevalence of microbes causing HAIs.

Genetic Manipulation as a Tool to Unravel Candida parapsilosis Species Complex Virulence and Drug Resistance: State of the Art

An increase in the rate of isolation of Candida parapsilosis in the past decade, as well as increased identification of azole-resistant strains are concerning, and require better understanding of virulence-like factors and drug-resistant traits of these species. In this regard, the present review “draws a line” on the information acquired, thus far, on virulence determinants and molecular mechanisms of antifungal resistance in these opportunistic pathogens, mainly derived from genetic manipulation studies. This will provide better focus on where we stand in our understanding of the C. parapsilosis species complex–host interaction, and how far we are from defining potential novel targets or therapeutic strategies—key factors to pave the way for a more tailored management of fungal infections caused by these fungal pathogens.

Resistance to Antifungal Drugs

Pathogenic fungi have several mechanisms of resistance to antifungal drugs, driven by the genetic plasticity and versatility of their homeostatic responses to stressful environmental cues. We critically review the molecular mechanisms of resistance and cellular adaptations of pathogenic fungi in response to antifungals and discuss the factors contributing to such resistance. We offer suggestions for the translational and clinical research agenda of this rapidly evolving and medically important field. A better understanding of antifungal resistance should assist in developing better detection tools and inform optimal strategies for preventing and treating refractory mycoses in the future.

Prevalence and Clonal Distribution of Azole-Resistant Candida parapsilosis Isolates Causing Bloodstream Infections in a Large Italian Hospital

The most prevalent cause of nosocomial bloodstream infection (BSI) among non-C. albicans Candida species, Candida parapsilosis, may not only be resistant to azole antifungal agents but also disseminate to vulnerable patients. In this survey of BSIs occurring at a large Italian hospital between May 2014 and May 2019, C. parapsilosis accounted for 28.5% (241/844) of all Candida isolates causing BSI episodes. The majority of episodes (151/844) occurred in medical wards. Across the 5 yearly periods, the rates of azole non-susceptibility were 11.8% (4/34), 17.8% (8/45), 28.6% (12/42), 32.8% (19/58), and 17.7% (11/62), respectively, using the Sensititre YeastOne® method. Among azole non-susceptible isolates (54/241; 22.4%), 49 were available for further investigation. Using the CLSI reference method, all 49 isolates were resistant to fluconazole and, except one (susceptible dose-dependent), to voriconazole. Forty (81.6%) isolates harbored the Erg11p Y132F substitution and nine (18.4%) isolates the Y132F in combination with the Erg11p R398I substitution. According to their genotypes, as defined using a microsatellite analysis based on six short tandem repeat markers, 87.7% of isolates (43/49) grouped in two major clusters (II and III), whereas 4.1% of isolates (2/49) belonged to a separate cluster (I). Interestingly, all the isolates from cluster II harbored the Y132F substitution, and those from cluster III harbored both Y132F and R398I substitutions. Of 56 non-Italian isolates included as controls, two Indian isolates with the Y132F substitution had a genotype clearly differing from that of the isolates from clusters II and I. In conclusion, these findings show the dominance of clonal Y132F isolates in our hospital and suggest detection of the Y132F substitution as helpful tool to prevent transmission among hospitalized patients at risk of BSI.

Antifungal susceptibility pattern and biofilm-related genes expression in planktonic and biofilm cells of Candida parapsilosis species complex

Background and Purpose:

Candida parapsilosis complex isolates are mainly responsible for nosocomial catheter-related infection in immunocompromised patients. Biofilm formation is regarded as one of the most pertinent key virulence factors in the development of these emerging infections. The present study aimed to compare in vitro antifungal susceptibility patterns and biofilm-related genes expression ratio in planktonic and biofilm’s cells of clinically C. parapsilosis complex isolates.

Materials and Methods:

The current study was conducted on a number of 17 clinical C. parapsilosis complex (10 C. parapsilosis sensu stricto, 5 C. orthopsilosis, and 2 C. metapsilosis). The antifungal susceptibility patterns of amphotericin B, fluconazole, itraconazole, voriconazole, posaconazole, and caspofungin in planktonic and biofilm forms were closely examined using CLSI M27-A3 broth microdilution method. The expression levels of biofilm-related genes (BCR1, EFG1, and FKS1) were evaluated in planktonic and biofilm’s cells using Real-time polymerase chain reaction (PCR) technique.

Results:

The obtained results indicated that all C. parapsilosis complex isolates were able to produce high and moderate amounts of biofilm forms. In addition, the sessile minimum inhibitory concentrations were reported to be high for fluconazole (≥ 64 µg/ml), itraconazole, voriconazole, and posaconazole (≥ 16 µg/ml), as compared to planktonic minimum inhibitory concentrations. Moreover, a significant difference was observed between antifungal susceptibility patterns for all azole antifungal agents (P<0.05). Furthermore, the BCR1 overexpression was considered significant in biofilms with regard to planktonic cells in C. parapsilosis species complex (P=0.002).

Conclusion:

C. parapsilosis complex isolates were found susceptible to most of the tested antifungal drugs, while biofilms demonstrated a noticeable resistant to azoles. The marked discrepancy noted in antifungal susceptibility patterns among these species should be highlighted to achieve effective therapeutic treatment.

Analysis of global antifungal surveillance results reveals predominance of Erg11 Y132F alteration among azole-resistant Candida parapsilosis and Candida tropicalis and country-specific isolate dissemination

This study evaluated the activity of echinocandins, azoles and amphotericin B against Candida spp. isolates and other yeasts and characterised azole resistance mechanisms in Candida parapsilosis and Candida tropicalis. Invasive Candida spp. isolates (n = 2936) collected in 60 hospitals worldwide during 2016-2017 underwent antifungal susceptibility testing by broth microdilution. Azole-resistant C. parapsilosis and C. tropicalis were submitted to qPCR for ERG11, CDR1 and MDR1, and the whole genome sequence was analysed. Results of non-susceptibility to echinocandins ranged from 0.0-2.3%, being highest in Candida glabrata. More than 99.0% of the Candida albicans isolates were susceptible to both fluconazole and voriconazole. Fluconazole resistance in C. glabrata was 6.5% overall, being highest in the USA (13.0%). Resistance to voriconazole in Candida krusei was only noted in the USA (5.0%). Azoles inhibited 89.1-91.6% of C. parapsilosis isolates, with most resistant isolates noted in Europe (15.1%), including 36 isolates from Italy (three hospitals), of which 34 harboured Erg11 Y132F mutations and overexpressed MDR1. Azole non-wild-type C. tropicalis (7/227) were found in five countries: 3 isolates from Thailand had the same Erg11 Y132F alteration. Fluconazole non-wild-type isolates were noted among 3/77 (3.9%) Candida dubliniensis, 4/17 (23.5%) Candida guilliermondii, 4/47 (8.5%) Candida lusitaniae and other less common yeast species. Echinocandin use has been recommended over fluconazole for invasive Candida infections. However, azoles are still active against the most common Candida spp. and resistance appears to be restricted to certain geographic regions and associated with Erg11 Y132 alterations in C. parapsilosis and C. tropicalis.

Molecular Identification, Genotypic Diversity, Antifungal Susceptibility, and Clinical Outcomes of Infections Caused by Clinically Underrated Yeasts, Candida orthopsilosis, and Candida metapsilosis: An Iranian Multicenter Study (2014-2019)

Despite the increasing occurrence of Candida orthopsilosis and Candida metapsilosis in clinical settings, little is known about their microbiological and clinical properties. Herein, we conducted a national retrospective study (2014–2019) from multiple centers in Iran. Among the 1,770 Candida isolates collected, we identified 600 Candida parapsilosis species complex isolates. Isolate identification was performed by 9-plex PCR, matrix-assisted laser desorption-time of flight mass spectrometry (MALDI-TOF MS), and rDNA sequencing, and antifungal susceptibility testing (AFST) followed CLSI M27-A3/S4; genotyping was performed by amplified fragment length polymorphism (AFLP) analysis; and clinical information was mined. Thirty-one isolates of C. orthopsilosis from various clinical sources, one mixed sample (blood) concurrently containing C. orthopsilosis and C. parapsilosis and one isolate of C. metapsilosis from a nail sample were identified. Although both 9-plex PCR and MALDI-TOF successfully identified all isolates, only 9-plex PCR could identify the agents in a mixed sample. For the C. orthopsilosis isolates, resistance (non-wild type) was noted only for itraconazole (n = 4; 12.5%). Anidulafungin and fluconazole showed the highest and voriconazole had the lowest geometric mean values. AFLP analysis showed three main and four minor genotypes. Interestingly, 90% of nail isolates clustered with 80% of the blood isolates within two clusters, and four blood isolates recovered from four patients admitted to a hospital clustered into two genotypes and showed a high degree of similarity (>99.2%), which suggests that C. orthopsilosis disseminates horizontally. Supported by our data and published case studies, C. orthopsilosis and C. metapsilosis can be linked to challenging clinical failures, and successful outcomes are not always mirrored by in vitro susceptibility. Accordingly, conducting nationwide studies may provide more comprehensive data, which is required for a better prognosis and clinical management of patients.

Precise genome editing using a CRISPR-Cas9 method highlights the role of CoERG11 amino acid substitutions in azole resistance in Candida orthopsilosis

Background

Azoles are one of the main antifungal classes for the treatment of candidiasis. In the current context of emerging drug resistance, most studies have focused on Candida albicans, Candida glabrata or Candida auris but, so far, less is known about the underlying mechanisms of resistance in other species, including Candida orthopsilosis.

Objectives

We investigated azole resistance in a C. orthopsilosis clinical isolate recovered from a patient with haematological malignancy receiving fluconazole prophylaxis.

Methods

Antifungal susceptibility to fluconazole was determined in vitro (CLSI M27-A3) and in vivo (in a Galleria mellonella model of invasive candidiasis). The CoERG11 gene was then sequenced and amino acid substitutions identified were mapped on the predicted 3D structure of CoErg11p. A clustered regularly interspaced short palindromic repeat-Cas9 (CRISPR-Cas9) genome-editing strategy was used to introduce relevant mutations into a fluconazole-susceptible C. orthopsilosis isolate.

Results

Compared with unrelated C. orthopsilosis isolates, the clinical isolate exhibited both in vitro and in vivo fluconazole resistance. Sequencing of the CoERG11 gene identified several amino acid substitutions, including two possibly involved in fluconazole resistance (L376I and G458S). Both mutations mapped close to the active site of CoErg11p. Engineering these mutations in a different genetic background using CRISPR-Cas9 demonstrated that G458S, but not L376I, confers resistance to fluconazole and voriconazole.

Conclusions

Our data show that the G458S amino acid substitution in CoERG11p, but not L376I, contributes to azole resistance in C. orthopsilosis. In addition to highlighting the potential of CRISPR-Cas9 technology for precise genome editing in the field of antifungal resistance, we discuss some points that are critical to improving its efficiency.

Limited ERG11 Mutations Identified in Isolates of Candida auris Directly Contribute to Reduced Azole Susceptibility

Multiple Erg11 amino acid substitutions were identified in clinical isolates of Candida auris originating from India and Colombia. Elevated azole MICs were detected in Saccharomyces cerevisiae upon heterologous expression of C. aurisERG11 alleles that encoded for Y132F or K143R substitutions; however, expression of alleles encoding I466M, Y501H, or other clade-defined amino acid differences yielded susceptible MICs. Similar to other Candida species, specific C. aurisERG11 mutations resulted directly in reduced azole susceptibility.