Synthesis of novel benzylamine antimycotics and evaluation of their antimycotic potency.

A series of 23 novel benzylamines was synthesized by reductive amination from halogen-substituted 3- and 4-benzyloxybenzaldehyde derivatives and 6-methylhept-2-yl amine or n-octylamine. The antimycotic activity of the resulting amines was evaluated in a microdilution assay against the apathogenic yeast Yarrowia lipolytica as test microorganism. Promising compounds were also tested against human pathogenic Candida species. The influence of halogen substituents at the benzyl ether side chain was studied in this screening, as well as the influence of the branched side chain of (±)-6-methylhept-2-yl amine in comparison with the n-octyl side chain.

Whole-genome sequencing confirms a persistent candidaemia clonal outbreak due to multidrug-resistant Candida parapsilosis.

OBJECTIVES: Although perceived as a rare clinical entity, recent studies have noted the emergence of MDR C. parapsilosis (MDR-Cp) isolates from single patients (resistant to both azole and echinocandins). We previously reported a case series of MDR-Cp isolates carrying a novel FKS1R658G mutation. Herein, we identified an echinocandin-naive patient infected with MDR-Cp a few months after the previously described isolates. WGS and CRISPR-Cas9 editing were used to explore the origin of the new MDR-Cp isolates, and to determine if the novel mutation confers echinocandin resistance. METHODS: WGS was applied to assess the clonality of these isolates and CRISPR-Cas9 editing and a Galleria mellonella model were used to examine whether FKS1R658G confers echinocandin resistance. RESULTS: Fluconazole treatment failed, and the patient was successfully treated with liposomal amphotericin B (LAMB). WGS proved that all historical and novel MDR-Cp strains were clonal and distant from the fluconazole-resistant outbreak cluster in the same hospital. CRISPR-Cas9 editing and G. mellonella virulence assays confirmed that FKS1R658G confers echinocandin resistance in vitro and in vivo. Interestingly, the FKS1R658G mutant showed a very modest fitness cost compared with the parental WT strain, consistent with the persistence of the MDR-Cp cluster in our hospital. CONCLUSIONS: Our study showcases the emergence of MDR-Cp isolates as a novel threat in clinical settings, which undermines the efficacy of the two most widely used antifungal drugs against candidiasis, leaving only LAMB as a last resort. Additionally, surveillance studies and WGS are warranted to effectively establish infection control and antifungal stewardship strategies.

Aspergillus terreus and the Interplay with Amphotericin B: from Resistance to Tolerance?

Aspergillus terreus is an opportunistic causative agent of invasive aspergillosis and, in most cases, it is refractory to amphotericin B (AMB) therapy. Notably, AMB-susceptible Aspergillus terreus sensu stricto (s.s.) representatives exist which are also associated with poor clinical outcomes. Such findings may be attributable to drug tolerance, which is not detectable by antifungal susceptibility testing. Here, we tested in vitro antifungal susceptibility (AFST) and the fungicidal activity of AMB against 100 clinical isolates of A. terreus species complex in RPMI 1640 and antibiotic medium 3 (AM3). MICs ranged from 0.5 to 16 µg/mL for RPMI 1640 and from 1 to >16 mg/L for AM3. AMB showed medium-dependent activity, with fungicidal effects only in antibiotic medium 3, not in RPMI 1640. Furthermore, the presence of AMB-tolerant phenotypes of A. terreus has been examined by assessing the minimum duration for killing 99% of the population (MDK99) and evaluating the data obtained in a Galleria mellonella infection model. A time-kill curve analysis revealed that A. terreus with AMB MICs of ≤1 mg/L (susceptible range) displayed AMB-tolerant phenotypes, exhibiting MDK99s at 18 and 36 h, respectively. Survival rates of infected G. mellonella highlighted that AMB was effective against susceptible A. terreus isolates, but not against tolerant or resistant isolates. Our analysis reveals that A. terreus isolates which are defined as susceptible based on MIC may comprise tolerant phenotypes, which may, in turn, explain the worse outcome of AMB therapy for phenotypically susceptible isolates.

The Zn2Cys6-type transcription factor LeuB cross-links regulation of leucine biosynthesis and iron acquisition in Aspergillus fumigatus.

Both branched-chain amino acids (BCAA) and iron are essential nutrients for eukaryotic cells. Previously, the Zn2Cys6-type transcription factor Leu3/LeuB was shown to play a crucial role in regulation of BCAA biosynthesis and nitrogen metabolism in Saccharomyces cerevisiae and Aspergillus nidulans. In this study, we found that the A. fumigatus homolog LeuB is involved in regulation of not only BCAA biosynthesis and nitrogen metabolism but also iron acquisition including siderophore metabolism. Lack of LeuB caused a growth defect, which was cured by supplementation with leucine or iron. Moreover, simultaneous inactivation of LeuB and HapX, a bZIP transcription factor required for adaptation to iron starvation, significantly aggravated the growth defect caused by inactivation of one of these regulators during iron starvation. In agreement with a direct role in regulation of both BCAA and iron metabolism, LeuB was found to bind to phylogenetically conserved motifs in promoters of genes involved in BCAA biosynthesis, nitrogen metabolism, and iron acquisition in vitro and in vivo, and was required for full activation of their expression. Lack of LeuB also caused activation of protease activity and autophagy via leucine depletion. Moreover, LeuB inactivation resulted in virulence attenuation of A. fumigatus in Galleria mellonella. Taken together, this study identified a previously uncharacterized direct cross-regulation of BCCA biosynthesis, nitrogen metabolism and iron homeostasis as well as proteolysis.

Synthesis, Biological Evaluation, and Structure-Activity Relationships of 4-Aminopiperidines as Novel Antifungal Agents Targeting Ergosterol Biosynthesis.

The aliphatic heterocycles piperidine and morpholine are core structures of well-known antifungals such as fenpropidin and fenpropimorph, commonly used as agrofungicides, and the related morpholine amorolfine is approved for the treatment of dermal mycoses in humans. Inspired by these lead structures, we describe here the synthesis and biological evaluation of 4-aminopiperidines as a novel chemotype of antifungals with remarkable antifungal activity. A library of more than 30 4-aminopiperidines was synthesized, starting from N-substituted 4-piperidone derivatives by reductive amination with appropriate amines using sodium triacetoxyborohydride. Antifungal activity was determined on the model strain Yarrowia lipolytica, and some compounds showed interesting growth-inhibiting activity. These compounds were tested on 20 clinically relevant fungal isolates (Aspergillus spp., Candida spp., Mucormycetes) by standardized microbroth dilution assays. Two of the six compounds, 1-benzyl-N-dodecylpiperidin-4-amine and N-dodecyl-1-phenethylpiperidin-4-amine, were identified as promising candidates for further development based on their in vitro antifungal activity against Candida spp. and Aspergillus spp. Antifungal activity was determined for 18 Aspergillus spp. and 19 Candida spp., and their impact on ergosterol and cholesterol biosynthesis was determined. Toxicity was determined on HL-60, HUVEC, and MCF10A cells, and in the alternative in vivo model Galleria mellonella. Analysis of sterol patterns after incubation gave valuable insights into the putative molecular mechanism of action, indicating inhibition of the enzymes sterol C14-reductase and sterol C8-isomerase in fungal ergosterol biosynthesis.

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.

Galleria mellonella as a model system to study virulence potential of mucormycetes and evaluation of antifungal treatment.

Mucorales can cause cutaneous to deep-seated infections, mainly in the immunocompromised host, resulting in high mortality rates due to late and inefficient treatment. In this study, Galleria mellonella larvae were evaluated as a heterologous invertebrate host to study pathogenicity of clinically relevant mucormycetes (Rhizopus spp., Rhizomucor spp., Lichtheimia spp., Mucor spp.). All tested species were able to infect G. mellonella larvae. Virulence potential was species-specific and correlated to clinical relevance. Survival of infected larvae was dependent on (a) the species (growth speed and spore size), (b) the infection dose, (c) the incubation temperature, (d) oxidative stress tolerance, and (e) iron availability in the growth medium. Moreover, we exploited the G. mellonella system to determine antifungal efficacy of liposomal amphotericin B, posaconazole, isavuconazole, and nystatin-intralipid. Outcome of in vivo treatment was strongly dependent upon the drug applied and the species tested. Nystatin-intralipid exhibited best activity against Mucorales, followed by posaconazole, while limited efficacy was seen for liposomal amphotericin B and isavuconazole. Pharmacokinetic properties of the tested antifungals within this alternative host system partly explain the limited treatment efficacy. In conclusion, G. mellonella represents a useful invertebrate infection model for studying virulence of mucormycetes, while evaluation of treatment response was limited.

Dihydroorotate dehydrogenase inhibitor olorofim exhibits promising activity against all clinically relevant species within Aspergillus section Terrei.

Objectives: In vitro and in vivo activity of the dihydroorotate dehydrogenase inhibitor olorofim (formerly F901318) (F2G Limited, UK) against clinically relevant species of the Aspergillus section Terrei was evaluated. Methods: A total of 92 clinical Aspergillus section Terrei isolates [42 Aspergillus terreus sensu stricto and 50 cryptic species: Aspergillus alabamensis (n = 8), Aspergillus citrinoterreus (n = 27), Aspergillus floccosus (n = 1), Aspergillus hortai (n = 13) and Aspergillus neoafricanus (n = 1)] were evaluated. MICs were determined using the CLSI M38-A2 method. MICs of olorofim were compared with those of posaconazole, voriconazole, itraconazole and amphotericin B. The in vivo efficacy of olorofim was determined in an immunosuppressed murine model of disseminated aspergillosis. Results: Olorofim was highly active against all tested Aspergillus section Terrei isolates, exhibiting an MIC range of 0.002-0.063 mg/L. Slightly higher MICs were observed for A. terreus cryptic species. Olorofim MICs were lower than those observed for the azoles. Selected strains with elevated MICs of azoles were highly susceptible to olorofim. Olorofim administered by oral and intravenous routes produced survival rates of 90%-100% in A. terreus-infected mice. Conclusions: Olorofim showed potent and consistent in vitro activity against all A. terreus strains tested, including those with elevated MICs of other antifungal substances. Overall, growth inhibition by olorofim was superior to that of azoles. In vivo data showed that olorofim was highly efficacious in prolonging survival of mice with disseminated aspergillosis due to A. terreus sensu stricto.

Sterol Composition of Clinically Relevant Mucorales and Changes Resulting from Posaconazole Treatment.

Mucorales are fungi with increasing importance in the clinics. Infections take a rapidly progressive course resulting in high mortality rates. The ergosterol biosynthesis pathway and sterol composition are of interest, since they are targeted by currently applied antifungal drugs. Nevertheless, Mucorales often exhibit resistance to these drugs, resulting in therapeutic failure. Here, sterol patterns of six clinically relevant Mucorales (Lichtheimia corymbifera, Lichtheimia ramosa, Mucor circinelloides, Rhizomucor pusillus, Rhizopus arrhizus, and Rhizopus microsporus) were analysed in a targeted metabolomics fashion after derivatization by gas chromatography-mass spectrometry. Additionally, the effect of posaconazole (POS) treatment on the sterol pattern of R. arrhizus was evaluated. Overall, fifteen different sterols were detected with species dependent variations in the total and relative sterol amount. Sterol analysis from R. arrhizus hyphae confronted with sublethal concentrations of posaconazole revealed the accumulation of 14-methylergosta-8,24-diene-3,6-diol, which is a toxic sterol that was previously only detected in yeasts. Sterol content and composition were further compared to the well-characterized pathogenic mold Aspergillus fumigatus. This work contributes to a better understanding of the ergosterol biosynthesis pathway of Mucorales, which is essential to improve antifungal efficacy, the identification of targets for novel drug design, and to investigate the combinatorial effects of drugs targeting this pathway.

Impact of Morphological Sectors on Antifungal Susceptibility Testing and Virulence Studies.

Morphological heterogeneity of Aspergillus terreus cultures was observed during continued cultivation of amphotericin B (AMB)-resistant isolates on drug-free medium. Outgrowth leads to the emergence of multiple sectors that might result from increased growth rates at drug-free conditions. We evaluated the differences in AMB susceptibility and virulence between sector subcultures (ATSec), AMB-resistant (ATR) strains, and AMB-susceptible (ATS) strains. By comparing A. terreus AMB-resistant (ATR) strains and A. terreus sector (ATSec) cultures we observed a highly significant reduction of AMB MICs in ATSec (ATR MIC, 2 to 32 µg/ml; ATSec MIC, 0.12 to 5 µg/ml). Furthermore, Galleria mellonella survival studies revealed an enhanced virulence of ATSec, which was comparable with that of AMB-sensitive Aspergillus terreus strains (median survival rates for ATS isolates, 72 h; for ATSec isolate ATSecG1, 84 h; for ATR isolates, 144 h). Our findings clearly demonstrate that spontaneous culture degeneration occurs in A. terreus and, most importantly, crucially impacts drug efficacy and virulence.

Oxidative Stress Response Tips the Balance in Aspergillus terreus Amphotericin B Resistance.

In this study, we characterize the impact of antioxidative enzymes in amphotericin B (AmB)-resistant (ATR) and rare AmB-susceptible (ATS) clinical Aspergillus terreus isolates. We elucidate expression profiles of superoxide dismutase (SOD)- and catalase (CAT)-encoding genes, enzymatic activities of SODs, and superoxide anion production and signaling pathways involved in the oxidative stress response (OSR) in ATS and ATR strains under AmB treatment conditions. We show that ATR strains possess almost doubled basal SOD activity compared to that of ATS strains and that ATR strains exhibit an enhanced OSR, with significantly higher sod2 mRNA levels and significantly increased cat transcripts in ATR strains upon AmB treatment. In particular, inhibition of SOD and CAT proteins renders resistant isolates considerably susceptible to the drug in vitro In conclusion, this study shows that SODs and CATs are crucial for AmB resistance in A. terreus and that targeting the OSR might offer new treatment perspectives for resistant species.

Effect of reduced oxygen on the antifungal susceptibility of clinically relevant aspergilli.

The influence of hypoxia on the in vitro activities of amphotericin B, azoles, and echinocandins against Aspergillus spp. was evaluated by comparing MICs, minimal fungicidal concentrations (MFCs), and epidemiological cutoffs (ECOFFs). Changes of MIC distributions due to hypoxia largely depend on the method, the species, and the growth ability under hypoxia. The activities of antifungals were not significantly altered under hypoxia, except for Aspergillus terreus, for which the activity changed from fungicidal to fungistatic.

Susceptibility profiles of amphotericin B and posaconazole against clinically relevant mucorales species under hypoxic conditions.

The effect of hypoxic conditions on the in vitro efficacy of amphotericin B and posaconazole against Mucorales was evaluated by defining MICs with Etest and broth microdilution and identifying minimal fungicidal concentrations (MFCs). With Etest, oxygen-dependent changes were detected, while the MIC and the MFC determined with broth microdilution remained unaltered with reduced oxygen levels. The observed differences depended on the method used.

N-Chlorotaurine Exhibits Fungicidal Activity against Therapy-Refractory Scedosporium Species and Lomentospora prolificans.

N-Chlorotaurine (NCT), a well-tolerated endogenous long-lived oxidant that can be applied topically as an antiseptic, was tested on its fungicidal activity against Scedosporium and Lomentospora, opportunistic fungi that cause severe infections with limited treatment options, mainly in immunocompromised patients. In quantitative killing assays, both hyphae and conidia of Scedosporium apiospermum, Scedosporium boydii, and Lomentospora prolificans (formerly Scedosporium prolificans) were killed by 55 mM (1.0%) NCT at pH 7.1 and 37°C, with a 1- to 4-log10 reduction in CFU after 4 h and a 4- to >6-log10 reduction after 24 h. The addition of ammonium chloride to NCT markedly increased this activity. LIVE/DEAD staining of conidia treated with 1.0% NCT for 0.5 to 3 h increased the permeability of the cell wall and membrane. Preincubation of the test fungi in 1.0% NCT for 10 to 60 min delayed the time to germination of conidia by 2 h to >12 h and reduced their germination rate by 10.0 to 100.0%. Larvae of Galleria mellonella infected with 1.0 × 10(7) conidia of S. apiospermum and S. boydii died at a rate of 90.0 to 100% after 8 to 12 days. The mortality rate was reduced to 20 to 50.0% if conidia were preincubated in 1.0% NCT for 0.5 h or if heat-inactivated conidia were used. Our study demonstrates the fungicidal activity of NCT against different Scedosporium and Lomentospora species. A postantifungal effect connected with a loss of virulence occurs after sublethal incubation times. The augmenting effect of ammonium chloride can be explained by the formation of monochloramine.

Etest cannot be recommended for in vitro susceptibility testing of mucorales.

Amphotericin B and posaconazole susceptibility patterns were determined for the most prevalent Mucorales, following EUCAST (European Committee on Antimicrobial Susceptibility Testing) broth microdilution guidelines. In parallel, Etest was performed and evaluated against EUCAST. The overall agreement of MICs gained with Etest and EUCAST was 75.1%; therefore, Etest cannot be recommended for antifungal susceptibility testing of Mucorales. Amphotericin B was the most active drug against Mucorales species in vitro, while the activities of posaconazole were more restricted.

Blocking Hsp70 enhances the efficiency of amphotericin B treatment against resistant Aspergillus terreus strains.

The polyene antifungal amphotericin B (AmB) is widely used to treat life-threatening fungal infections. Even though AmB resistance is exceptionally rare in fungi, most Aspergillus terreus isolates exhibit an intrinsic resistance against the drug in vivo and in vitro. Heat shock proteins perform a fundamental protective role against a multitude of stress responses, thereby maintaining protein homeostasis in the organism. In this study, we elucidated the role of heat shock protein 70 (Hsp70) family members and compared resistant and susceptible A. terreus clinical isolates. The upregulation of cytoplasmic Hsp70 members at the transcriptional as well as translational levels was significantly higher with AmB treatment than without AmB treatment, particularly in resistant A. terreus isolates, thereby indicating a role of Hsp70 proteins in the AmB response. We found that Hsp70 inhibitors considerably increased the susceptibility of resistant A. terreus isolates to AmB but exerted little impact on susceptible isolates. Also, in in vivo experiments, using the Galleria mellonella infection model, cotreatment of resistant A. terreus strains with AmB and the Hsp70 inhibitor pifithrin-µ resulted in significantly improved survival compared with that achieved with AmB alone. Our results point to an important mechanism of regulation of AmB resistance by Hsp70 family members in A. terreus and suggest novel drug targets for the treatment of infections caused by resistant fungal isolates.

Alternative in-vivo models of mucormycosis.

Mucormycosis is still regarded a rare fungal infection, but the high incidences of COVID-associated cases in India and other countries have shown its potential threat to large patient cohorts. In addition, infections by these fast-growing fungi are often fatal and cause disfigurement, badly affecting patients' lives. In advancing our understanding of pathogenicity factors involved in this disease, to enhance the diagnostic toolset and to evaluate novel treatment regimes, animal models are indispensable. As ethical and practical considerations typically favor the use of alternative model systems, this review provides an overview of alternative animal models employed for mucormycosis and discusses advantages and limitations of the respective model.

H3K4 methylation regulates development, DNA repair, and virulence in Mucorales.

Mucorales are basal fungi that opportunistically cause a potentially fatal infection known as mucormycosis (black fungus disease), which poses a significant threat to human health due to its high mortality rate and its recent association with SARS-CoV-2 infections. On the other hand, histone methylation is a regulatory mechanism with pleiotropic effects, including the virulence of several pathogenic fungi. However, the role of epigenetic changes at the histone level never has been studied in Mucorales. Here, we dissected the functional role of Set1, a histone methyltransferase that catalyzes the methylation of H3K4, which is associated with the activation of gene transcription and virulence. A comparative analysis of the Mucor lusitanicus genome (previously known as Mucor circinelloides f. lusitanicus) identified only one homolog of Set1 from Candida albicans and Saccharomyces cerevisiae that contains the typical SET domain. Knockout strains in the gene set1 lacked H3K4 monomethylation, dimethylation, and trimethylation enzymatic activities. These strains also showed a significant reduction in vegetative growth and sporulation. Additionally, set1 null strains were more sensitive to SDS, EMS, and UV light, indicating severe impairment in the repair process of the cell wall and DNA lesions and a correlation between Set1 and these processes. During pathogen-host interactions, strains lacking the set1 gene exhibited shortened polar growth within the phagosome and attenuated virulence both in vitro and in vivo. Our findings suggest that the histone methyltransferase Set1 coordinates several cell processes related to the pathogenesis of M. lusitanicus and may be an important target for future therapeutic strategies against mucormycosis.

cotH Genes Are Necessary for Normal Spore Formation and Virulence in Mucor lusitanicus.

Mucormycosis is an invasive fungal infection caused by certain members of the fungal order of Mucorales. The species most frequently identified as the etiological agents of mucormycosis belong to the genera Rhizopus, Lichtheimia, and Mucor. The frequency of systemic mucormycosis has been increasing, mainly because of increasing numbers of susceptible patients. Furthermore, Mucorales display intrinsic resistance to the majority of routinely used antifungal agents (e.g., echinocandins and short-tailed azoles), which limits the number of possible therapeutic options. All the above-mentioned issues urge the improvement of molecular identification methods and the discovery of new antifungal targets and strategies. Spore coat proteins (CotH) constitute a kinase family present in many pathogenic bacteria and fungi and participate in the spore formation in these organisms. Moreover, some of them can act as virulence factors being receptors of the human GRP78 protein during Rhizopus delemar-induced mucormycosis. We identified 17 cotH-like genes in the Mucor lusitanicus genome database. Successful disruption of five cotH genes in Mucor was performed using the CRISPR-Cas9 system. The CotH3 and CotH4 proteins play a role in adaptation to different temperatures as well as in developing the cell wall structure. We also show CotH4 protein is involved in spore wall formation by affecting the total chitin content and, thus, the composition of the spore wall. The role of CotH3 and CotH4 proteins in virulence was confirmed in two invertebrate models and a diabetic ketoacidosis (DKA) mouse model. IMPORTANCE Current treatment options for mucormycosis are inadequate, resulting in high mortality rates, especially among immunosuppressed patients. The development of novel therapies for mucormycosis has been hampered by lack of understanding of the pathogenetic mechanisms. The importance of the cell surface CotH proteins in the pathogenesis of Rhizopus-mediated mucormycosis has been recently described. However, the contribution of this family of proteins to the virulence of other mucoralean fungi and their functionality in vital processes remain undefined. Through the use of the CRISPR-Case9 gene disruption system, we demonstrate the importance of several of the CotH proteins to the virulence of Mucor lusitanicus by using three infection models. We also report on the importance of one of these proteins, CotH4, to spore wall formation by affecting chitin content. Therefore, our studies extend the importance of CotH proteins to Mucor and identify the mechanism by which one of the CotH proteins contributes to the development of a normal fungal cell wall, thereby indicating that this family of proteins can be targeted for future development of novel therapeutic strategies of mucormycosis.

Candida parapsilosis isolates carrying mutations outside FKS1 hotspot regions confer high echinocandin tolerance and facilitate the development of echinocandin resistance.

Candida parapsilosis is a significant cause of candidemia worldwide. Echinocandin-resistant (ECR) and echinocandin-tolerant (ECT) C. parapsilosis isolates have been reported in various countries but are rare. Resistance and tolerance are predominantly caused by mutations related to the hotspot (HS) regions of the FKS1 gene. A relatively high proportion of clinical C. parapsilosis isolates carrying mutations outside the HS regions has been noted in some studies, but an association with echinocandin (EC) resistance or tolerance was not explored. Herein, CRISPR-Cas9 was used and the association between amino acid substitution in FKS1 outside HS 1/2 (V595I, S745L, M1328I, F1386S, and A1422G) with EC susceptibility profile was delineated. None of the mutations conferred EC resistance, but they resulted in a significantly higher level of EC tolerance than the parental isolate, ATCC 22019. When incubated on agar plates containing ECs, specifically caspofungin and micafungin, ECR colonies were exclusively observed among ECT isolates, particularly mutants carrying V595I, S745L, and F1386S. Additionally, mutants had significantly better growth rates in yeast extract peptone dextrose (YPD) and YPD containing agents inducing membrane and oxidative stresses. The mutants had a trivial fitness cost in the Galleria mellonella model relative to ATCC 22019. Collectively, this study supports epidemiological studies to catalog mutations occurring outside the HS regions of FKS1, even if they do not confer EC resistance. These mutations are important as they potentially confer a higher level of EC tolerance and a higher propensity to develop EC resistance, therefore unveiling a novel mechanism of EC tolerance in C. parapsilosis. The identification of EC tolerance in C. parapsilosis may have direct clinical benefit in patient management.