Role of FKS Gene in the Susceptibility of Pathogenic Fungi to Echinocandins

In the flow of molecular miniaturized fungal diagnosis

The diagnosis of fungal infections presents several challenges and limitations, stemming from the similarities in symptomatology, diversity of underlying pathogenic species, complexity of fungal biology, and scarcity of rapid, affordable, and point-of-care approaches. In this review, we assess technological advances enabling the conversion of cutting-edge laboratory molecular diagnostic methods to cost-effective microfluidic devices. The most promising strategies toward the design of DNA sequence-based fungal diagnostic systems, capable of capturing and deciphering the highly informative DNA of the pathogen and adapted for resource-limited settings, are discussed, bridging fungal biology, molecular genetics, microfluidics, and biosensors.

Risk factors and mortality of the newly emerging Candida auris in a university hospital in Saudi Arabia

Candida auris presents a global health threat. We investigated risk factors and mortality of Candida auris infections in a retrospective study in Saudi Arabia. We included 27 patients ≥14  with invasive Candida auris from 2015-2022, with median age 58, and 66.7% males. All patients had indwelling devices. The most common infection sources were central line-associated bloodstream infection in 17 (63.0%), and urinary tract infections in four (12%). Fever and shock were observed in nine patients (33.3%) each, and 22 (81%) were admitted to the intensive care unit. Common comorbidities were diabetes and heart disease in 13 (48.1%) patients each. The median hospital stay was 78 days, and the median Charlson index was 4. The C. auris cultures were 100% susceptible to voriconazole, caspofungin, and amphotericin, while three were fully susceptible to fluconazole (11.1%). Despite treatment, 18 (66.7%) patients died. In conclusion, invasive C. auris infection had varied presentations. All patients had indwelling devices, and many had lengthy hospital stays. All isolates were susceptible to amphotericin and echinocandins, while few were fully susceptible to fluconazole.

Serine/Threonine Phosphatase Calcineurin Orchestrates the Intrinsic Resistance to Micafungin in the Human-Pathogenic Fungus Mucor circinelloides

Procedures such as solid-organ transplants and cancer treatments can leave many patients in an immunocompromised state. This leads to their increased susceptibility to opportunistic diseases such as fungal infections. Mucormycosis infections are continually emerging and pose a serious threat to immunocompromised patients. Recently there has been a sharp increase in mucormycosis cases as a secondary infection in patients battling severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. Mucorales fungi are notorious for presenting resistance to most antifungal drugs. The absence of effective means to treat these infections results in mortality rates approaching 100% in cases of disseminated infection. One of the most effective antifungal drug classes currently available is the echinocandins. Echinocandins seem to be efficacious in the treatment of many other fungal infections. Unfortunately, susceptibility testing has found that echinocandins have little to no effect on Mucorales fungi. In this study, we found that the model Mucorales Mucor circinelloides genome carries three copies of the genes encoding the echinocandin target protein β-(1,3)-d-glucan synthase (fksA, fksB, and fksC). Interestingly, we found that exposing M. circinelloides to micafungin significantly increased the expression of the fksA and fksB genes, resulting in an increased accumulation of β-(1,3)-d-glucan on the cell walls. However, this overexpression of the fks genes is not directly connected to the intrinsic resistance. Subsequent investigation discovered that the serine/threonine phosphatase calcineurin regulates the expression of fksA and fksB, and the deletion of calcineurin results in a decrease in expression of all three fks genes. Deletion of calcineurin also results in a lower minimum effective concentration (MEC) of micafungin. In addition, we found that duplication of the fks gene is also responsible for the intrinsic resistance, in which lack of either fksA or fksB led a lower MEC of micafungin. Together, these findings demonstrate that calcineurin and fks gene duplication contribute to the intrinsic resistance to micafungin we observe in M. circinelloides.

Risk Factors and Clinical Characteristics of Patients with Ocular Candidiasis

Ocular candidiasis is a critical and challenging complication of candidemia. The purpose of this study was to investigate the appropriate timing for ophthalmologic examinations, risk factors for complications of ocular lesions, and their association with mortality. This retrospective cohort study applied, using multiple logistic regression analysis and Cox regression models, to cases of candidemia (age ≥ 18 years) for patients who underwent ophthalmologic consultation. Of the 108 candidemia patients who underwent ophthalmologic examination, 27 (25%) contracted patients had ocular candidiasis, and 7 experienced the more severe condition of endophthalmitis, which included subjective ocular symptoms. In most cases, the initial ophthalmologic examination was performed within one week of the onset of candidiasis with a diagnosis of ocular candidiasis, but in three cases, the findings became apparent only after a second examination within 7−14 days after onset of candidiasis. The independent risk factor extracted for the development of ocular candidiasis was the isolation of C. albicans (OR, 4.85; 95% CI, 1.58−14.90), unremoved CVC (OR, 10.40; 95% CI, 1.74−62.16), and a high βDG value (>108.2 pg/mL) (HR, 2.83; 95% CI = 1.24−6.27). Continuous ophthalmologic examination is recommended in cases of candidemia with the above risk factors with an initial examination within 7 days of onset and a second examination 7−14 days after onset.

Caspofungin resistance in Candida albicans: genetic factors and synergistic compounds for combination therapies

Caspofungin and other echinocandins have been used for the treatment of human infections by the opportunistic yeast pathogen, Candida albicans. There has been an increase in infections by non-albicans Candida species such as Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida krusei, and Candida auris in clinical or hospital settings. This is problematic to public health due to the increasing prevalence of echinocandin resistant species/strains. This review will present a summary on various studies that investigated the inhibitory action of caspofungin on 1,3-β-D-glucan synthesis, on cell wall structure, and biofilm formation of C. albicans. It will highlight some of the issues linked to caspofungin resistance or reduced caspofungin sensitivity in various Candida species and the potential benefits of antimicrobial peptides and other compounds in synergy with caspofungin.

[Systemic antifungal drugs]

Invasive fungal infections have increased over the last decades and the therapeutic choices to treat them are limited. The antifungal agents currently available are useful and have optimal in vitro activity; however, their activity can be lowered due to the development of fungal resistance. The increase in primary or secondary resistance to some antifungal drugs has led to the search of alternatives such as the combination of drugs or the development of new antifungals. In this paper, the activity of the main families of antifungal drugs, polyenes, azoles, echinocandins, 5-fluorocytosine and other new antifungal drugs, are reviewed. The main resistance mechanisms developed by fungi are also described.

Characteristics, Risk Factors, and Survival Analysis of Candida auris Cases: Results of One-Year National Surveillance Data from Oman

Background: Candida auris (C. auris) is an emerging healthcare-associated pathogen resulting in significant morbidity and mortality. The aim of this study is to report data from the national C. auris surveillance system for 2019 and conduct a survival analysis of the reported cohort. Methods: a retrospective analysis was conducted for all C. auris cases reported nationally to the Oman Antimicrobial Surveillance System (OMASS) in 2019, and isolates were sent to the Central Public Health Laboratories (CPHL). Clinical and demographic data were obtained through the E-Surveillance reporting system and the Electronic System (NEHR Al-Shifa) at CPHL. Statistical analysis was done using Kaplan–Meier analysis and Cox proportional hazard models. Results: One hundred and twenty-nine isolates of C. auris were grown from 108 inpatients; 87% were isolated from clinical samples, of which blood was the most common (38.9%). Forty (37%) were ≥65 years of age, 72 (66.7%) were males, and 85 (78.7%) were Omani nationals. Of the total isolates, 43.5% were considered as colonization; 56.5% were considered infection, of which 61.8% of them were candidemia. At least one risk factor was present in 98.1% of patients. The mean time from admission to infection was 1.7 months (SD = 2.8), and the mean length of hospital stay was 3.5 months (SD = 4). Totals of 94.8% and 96.1% of the isolates were non-susceptible to fluconazole and amphotericin, respectively. The variables found to be significantly associated with longer survival post C. auris diagnosis (p < 0.05) were age < 65 years, absence of comorbidities, length of stay < 3 months, colonization, and absence of candidemia. The infection fatality rate was 52.5%. Conclusion: Including C. auris in an ongoing antimicrobial surveillance program provides important data for the comprehensive management of this growing public health threat. The current study shows health care outbreaks of C. auris are ongoing, with 52.5% infection fatality, although our isolates remained sensitive to Echinocandins in vitro.

Rezafungin-Mechanisms of Action, Susceptibility and Resistance: Similarities and Differences with the Other Echinocandins

Rezafungin (formerly CD101) is a new β-glucan synthase inhibitor that is chemically related with anidulafungin. It is considered the first molecule of the new generation of long-acting echinocandins. It has several advantages over the already approved by the Food and Drug Administration (FDA) echinocandins as it has better tissue penetration, better pharmacokinetic/phamacodynamic (PK/PD) pharmacometrics, and a good safety profile. It is much more stable in solution than the older echinocandins, making it more flexible in terms of dosing, storage, and manufacturing. These properties would allow rezafungin to be administered once-weekly (intravenous) and to be potentially administered topically and subcutaneously. In addition, higher dose regimens were tested with no evidence of toxic effect. This will eventually prevent (or reduce) the selection of resistant strains. Rezafungin also has several similarities with older echinocandins as they share the same in vitro behavior (very similar Minimum Inhibitory Concentration required to inhibit the growth of 50% of the isolates (MIC50) and half enzyme maximal inhibitory concentration 50% (IC50)) and spectrum, the same target, and the same mechanisms of resistance. The selection of FKS mutants occurred at similar frequency for rezafungin than for anidulafungin and caspofungin. In this review, rezafungin mechanism of action, target, mechanism of resistance, and in vitro data are described in a comparative manner with the already approved echinocandins.

Iron Assimilation during Emerging Infections Caused by Opportunistic Fungi with emphasis on Mucorales and the Development of Antifungal Resistance

Iron is a key transition metal required by most microorganisms and is prominently utilised in the transfer of electrons during metabolic reactions. The acquisition of iron is essential and becomes a crucial pathogenic event for opportunistic fungi. Iron is not readily available in the natural environment as it exists in its insoluble ferric form, i.e., in oxides and hydroxides. During infection, the host iron is bound to proteins such as transferrin, ferritin, and haemoglobin. As such, access to iron is one of the major hurdles that fungal pathogens must overcome in an immunocompromised host. Thus, these opportunistic fungi utilise three major iron acquisition systems to overcome this limiting factor for growth and proliferation. To date, numerous iron acquisition pathways have been fully characterised, with key components of these systems having major roles in virulence. Most recently, proteins involved in these pathways have been linked to the development of antifungal resistance. Here, we provide a detailed review of our current knowledge of iron acquisition in opportunistic fungi, and the role iron may have on the development of resistance to antifungals with emphasis on species of the fungal basal lineage order Mucorales, the causative agents of mucormycosis.

Rezafungin In Vitro Activity against Contemporary Nordic Clinical Candida Isolates and Candida auris Determined by the EUCAST Reference Method

Rezafungin (formerly CD101) is a novel echinocandin in clinical development. EUCAST epidemiological cutoff values (ECOFFs) have not yet been established. We determined the in vitro activity of rezafungin and comparators against 1,293 Nordic yeast isolates and 122 Indian Candida auris isolates and established single-center wild-type upper limits (WT-UL). The isolates (19 Candida spp. and 13 other yeast species) were identified using Chromagar; matrix-assisted laser desorption ionization-time of flight (MALDI-TOF); and, when needed, internal transcribed spacer sequencing. EUCAST E.Def 7.3.1 susceptibility testing included rezafungin, anidulafungin, micafungin, amphotericin B, and fluconazole. WT-UL were established following EUCAST principles for visual and statistical ECOFF setting. fks target genes were sequenced for rezafungin non-wild-type isolates. EUCAST clinical breakpoints for fungi version 9.0 were adopted for susceptibility classification. Rezafungin had species-specific activity similar to that of anidulafungin and micafungin. On a milligram-per-liter basis, rezafungin was overall less active than anidulafungin and micafungin but equally or more active than fluconazole and amphotericin B against the most common Candida species, except C. parapsilosis We identified 37 (3.1%) rezafungin non-wild-type isolates of C. albicans (1.9%), C. glabrata (3.0%), C. tropicalis (2.7%), C. dubliniensis (2.9%), C. krusei (1.2%), and C. auris (14.8%). Alterations in Fks hot spots were found in 26/26 Nordic and 8/18 non-wild-type C. auris isolates. Rezafungin displayed broad in vitro activity against Candida spp., including C. auris Adopting WT-UL established here, few Nordic strains, but a significant proportion of C. auris isolates, had elevated MICs with mutations in fks target genes that conferred echinocandin cross-resistance. fks1 mutations raised rezafungin MICs notably less than anidulafungin and micafungin MICs in C. auris.

Killing kinetics of anidulafungin, caspofungin and micafungin against Candida parapsilosis species complex: Evaluation of the fungicidal activity

BACKGROUND

Candida parapsilosis, Candida metapsilosis and Candida orthopsilosis are emerging as relevant causes of candidemia. Moreover, they show differences in their antifungal susceptibility and virulence. The echinocandins are different in terms of in vitro antifungal activity against Candida. Time-kill (TK) curves represent an excellent approach to evaluate the fungicidal activity of antifungal drugs.

AIMS

To compare the fungicidal activities of anidulafungin, caspofungin and micafungin against C. parapsilosis species complex by TK curves.

METHODS

Antifungal activities of three echinocandins against C. parapsilosis, C. metapsilosis and C. orthopsilosis were studied by TK curves. Drug concentrations assayed were 0.25, 2 and 8μg/ml. CFU/ml were determined at 0, 2, 4, 6, 24 and 48h.

RESULTS

Killing activities of echinocandins were species-, isolates- and concentration-dependent. Anidulafungin reached the fungicidad endpoint for 6 out of 7 isolates (86%); it required between 13.34 and 29.67h to reach this endpoint for the three species studied, but more than 48h were needed against one isolate of C. orthopsilosis (8μg/ml). Caspofungin fungicidal endpoint was only achieved with 8μg/ml against one isolate of C. metapsilosis after 30.12h (1 out of 7 isolates; 14%). Micafungin fungicidal endpoint was reached in 12.74-28.38h (8μg/ml) against one isolate each of C. parapsilosis and C. orthopsilosis, and against both C. metapsilosis isolates (4 out of 7 isolates; 57%).

CONCLUSIONS

C. metapsilosis was the most susceptible species to echinocandins, followed by C. orthopsilosis and C. parapsilosis. Anidulafungin was the most active echinocandin against C. parapsilosis complex.

The fungal cell wall as a target for the development of new antifungal therapies

In the past three decades invasive mycoses have globally emerged as a persistent source of healthcare-associated infections. The cell wall surrounding the fungal cell opposes the turgor pressure that otherwise could produce cell lysis. Thus, the cell wall is essential for maintaining fungal cell shape and integrity. Given that this structure is absent in host mammalian cells, it stands as an important target when developing selective compounds for the treatment of fungal infections. Consequently, treatment with echinocandins, a family of antifungal agents that specifically inhibits the biosynthesis of cell wall (1-3)β-D-glucan, has been established as an alternative and effective antifungal therapy. However, the existence of many pathogenic fungi resistant to single or multiple antifungal families, together with the limited arsenal of available antifungal compounds, critically affects the effectiveness of treatments against these life-threatening infections. Thus, new antifungal therapies are required. Here we review the fungal cell wall and its relevance in biotechnology as a target for the development of new antifungal compounds, disclosing the most promising cell wall inhibitors that are currently in experimental or clinical development for the treatment of some invasive mycoses.