Unpredictable In Vitro Killing Activity of Amphotericin B against Four Candida auris Clades

A comprehensive analysis of the effect of quorum-sensing molecule 3-oxo-C12-homoserine lactone on Candida auris and Candida albicans

Candida auris occupies similar niches in various infections as Pseudomonas aeruginosa; however, the details of their interspecies communication remain largely unknown. To gain deeper insights into this relationship, phenotypic and transcriptomic analyses were conducted in the presence of the primary P. aeruginosa quorum-sensing molecule, N-(3-oxododecanoyl)-l-homoserine lactone (HSL), against C. auris, with the results compared to those of C. albicans. Our findings indicate that HSL-induced effects are not specific to C. albicans; additionally, several characteristics are present in C. auris but not in C. albicans following HSL exposure. Significant HSL-induced reduction was observed in growth and adhesion of C. auris cells in time -and concentration-dependent way (p < 0.01-0.001). Moreover, HSL reduced intracellular iron and zinc levels (p < 0.05-0.001); furthermore, it modulated C. auris metabolism toward beta-oxidation, which may be associated with the observed reduction in in vivo virulence at lower HSL concentrations compared with C. albicans. RNA-sequencing transcriptome analysis of C. auris revealed 67 and 306 upregulated genes, as well as 111 and 168 downregulated genes, in response to 100 and 200-μM HSL, respectively. We identified 45 overlapping upregulated and 25 overlapping downregulated genes between the two HSL concentrations. Similar to other Candida-derived C12 compounds (e.g., farnesol), HSL reduces several C. auris survival strategies, which may significantly influence the nature of P. aeruginosa-C. auris co-habitation. In conclusion, the obtained findings on C. auris do not provide clear evidence that HSL mediated effects have any favourable consequences in terms of P. aeruginosa-C. auris co-colonisation and/or co-infections.

Tenebrio molitor (Coleoptera: Tenebrionidae) as an alternative host for the study of pathogenicity in Candida auris

BACKGROUND

Candida auris, a multidrug-resistant fungal pathogen, has emerged as a significant global health threat due to its high transmission and mortality rates, especially in healthcare settings.

OBJECTIVE

This study aimed to establish the larvae of the coleopteran Tenebrio molitor (mealworm) as an in vivo model to evaluate the virulence of different C. auris strains.

METHODS

T. molitor larvae were inoculated with varying doses and strains of C. auris. Mortality rates were monitored, melanization responses, and phenoloxidase activity were assessed. Histopathological analyses were conducted to observe tissue invasion by the yeast cells. Additionally, a biofilm formation test was included as a complementary analysis to determine if biofilm production would influence the virulence of the C. auris strains.

RESULTS

A dose-dependent increase in mortality was observed, with the highest fungal load leading to the highest mortality rates. The study also revealed significant differences in virulence among the strains, with those from Kuwait and the reference strain CBS 10913 showing the highest pathogenicity. Melanization rates were significantly higher in infected larvae, indicating an active immune response. The histopathological analysis revealed the presence of C. auris cells within the tissue of T. molitor larvae. However, the biofilm formation complementary test did not show a significant difference in virulence among the different clades of C. auris.

CONCLUSION

The T. molitor model effectively demonstrated the pathogenic potential and virulence differences of C. auris strains. Strains from Kuwait and the reference strain CBS 10913 exhibited the highest virulence, causing 100 % mortality within 24 h. The model also highlighted significant biofilm formation and melanization responses, correlating with fungal burden. This insect model provides a valuable and cost-effective tool for preliminary virulence screening of clinical yeast strains, offering insights into host-pathogen interactions and the potential for evaluating antifungal treatments in vivo.

Cerebrospinal Drain Infection by Candida auris: A Case Report and Review of the Literature

Candida auris is notorious for its ability to spread within healthcare environments, particularly in intensive care units (ICUs), posing significant challenges for clinicians as treatment options become limited. This is especially concerning in the context of central nervous system (CNS)-invasive infections. While rare, its involvement in nosocomial brain ventriculitis presents substantial diagnostic and therapeutic challenges, with no established guidelines for managing CNS infections caused by Candida auris. This report presents a case of Candida auris ventriculitis in an ICU patient and offers a comprehensive and targeted literature review, emphasizing diagnostic approaches, treatment strategies, and the clinical complexities of managing this emerging pathogen in CNS infections.

Defining Optimal Doses of Liposomal Amphotericin B Against Candida auris: Data From an In Vitro Pharmacokinetic/Pharmacodynamic Model

BACKGROUND

Candida auris isolates exhibit elevated amphotericin B (AMB) minimum inhibitory concentrations (MICs). As liposomal AMB (L-AMB) can be safely administered at high doses, we explored L-AMB pharmacodynamics against C. auris isolates in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) dilution model.

METHODS

Four C. auris isolates with Clinical and Laboratory Standards Institute (CLSI) AMB MICs = 0.5-2 mg/L were tested in an in vitro PK/PD model simulating L-AMB pharmacokinetics. The in vitro model was validated using a Candida albicans isolate tested in animals. The peak concentration (Cmax)/MIC versus log10 colony-forming units (CFU)/mL reduction from the initial inoculum was analyzed with the sigmoidal model with variable slope (Emax model). Monte Carlo analysis was performed for the standard (3 mg/kg) and higher (5 mg/kg) L-AMB doses.

RESULTS

The in vitro PK/PD relationship Cmax/MIC versus log10 CFU/mL reduction followed a sigmoidal pattern (R2 = 0.91 for C. albicans, R2 = 0.86 for C. auris). The Cmax/MIC associated with stasis was 2.1 for C. albicans and 9 for C. auris. The probability of target attainment was >95% with 3 mg/kg for wild-type C. albicans isolates with MIC ≤2 mg/L and C. auris isolates with MIC ≤1 mg/L whereas 5 mg/kg L-AMB is needed for C. auris isolates with MIC 2 mg/L.

CONCLUSIONS

L-AMB was 4-fold less active against C. auris than C. albicans. Candida auris isolates with CLSI MIC 2 mg/L would require a higher L-AMB dose.

Efficacy of the combination of amphotericin B and echinocandins against Candida auris in vitro and in the Caenorhabditis elegans host model

IMPORTANCE

Multidrug resistance is a rising problem among non-Candida albicans species, such as Candida auris. This therapeutic problem has been very important during the COVID-19 pandemic. The World Health Organization has included C. auris in its global priority list of health-threatening fungi, to study this emerging multidrug-resistant species and to develop effective alternative therapies. In the present study, the synergistic effect of the combination of amphotericin B and echinocandins has been demonstrated against blood isolates of C. auris. Different susceptibility responses were also observed between aggregative and non-aggregative phenotypes. The antifungal activity of these drug combinations against C. auris was also demonstrated in the Caenorhabditis elegans host model of candidiasis, confirming the suitability and usefulness of this model in the search for solutions to antimicrobial resistance.

PK/PD modeling and simulation of the in vitro activity of the combinations of isavuconazole with echinocandins against Candida auris

In vitro combination of echinocandins and isavuconazole against the emerging species Candida auris is mainly synergistic. However, this combination has not been evaluated in clinical settings. A pharmacokinetic/pharmacodynamic modeling and simulation approach based on in vitro data may be helpful to further study the therapeutic potential of these combinations. Therefore, the aims of this study were to characterize the time course of growth and killing of C. auris in response to the combination of the three approved echinocandins and isavuconazole using a semimechanistic model and to perform model-based simulations in order to predict the in vivo response to combination therapy. In vitro static time-kill curve data for isavuconazole and echinocandins combinations against six blood isolates of C. auris were best modeled considering the total killing of the fungal population as dependent on the additive effects of both drugs. Once assessed, the predictive performance of the model using simulations of different dosing and fungal susceptibility scenarios were conducted. Model-based simulations revealed that none of the combinations at standard or higher dosages would be effective against the studied isolates of C. auris and it was predicted that the combinations of isavuconazole with anidulafungin or caspofungin would be effective for minimum inhibitory concentrations up to 0.03 and 0.06 mg/L respectively, whereas the combination with micafungin would lead to treatment failure. The current approach highlights the importance of bridging the in vitro results to the clinic.

In Vivo Efficacy of Amphotericin B against Four Candida auris Clades

Candida auris is a multidrug-resistant fungus against which in some clinical situations amphotericin B (AMB) remains the alternative or first line drug. We compared daily 1 mg/kg of AMB efficacy in a neutropenic murine bloodstream infection model against 10 isolates representing four C. auris clades (South Asian n = 2; East Asian n = 2; South African n = 2; South American n = 4; two of which were of environmental origin). Five days of AMB treatment significantly increased the survival rates in mice infected with isolates of the East Asian clade, and 1 isolate each from the South African and South American clades (originated from bloodstream), but not in mice infected with the South Asian and 2 environmental isolates from the South American clades. AMB treatment decreased the fungal burden in mice infected with the 2 isolates each from East Asian and South African, and 1 out of 2 bloodstream isolates from South American clades in the hearts (p < 0.01), kidneys (p < 0.01) and brain (p < 0.05). AMB treatment, regardless of clades, significantly decreased colony forming units in the urine at day 3. However, histopathological examination in AMB-treated mice revealed large aggregates of yeast cells in the kidneys and hearts, and focal lesions in the cerebra and cerebelli, regardless of precise C. auris clade. Our clade-specific data confirm that the efficacy of AMB against C. auris is weak, explaining the therapeutic failures in clinical situations. Our results draw attention to the necessity to maximize the killing at the start of treatment to avoid later complications in the heart and central nervous system.

Expert recommendations for prevention and management of Candida auris transmission

Candida auris was first described as a yeast pathogen in 2009. Since then, the new species has emerged worldwide. In contrast to most other Candida spp., C. auris frequently exhibits multi-drug resistance and is readily transmitted in hospital settings. While most isolations so far are from colonized patients, C. auris does cause life-threatening invasive infections. During management of the first documented C. auris transmission in a German hospital, experts from the National Reference Centers for Invasive Fungal Infections (NRZMyk) and the National Reference Center for Surveillance of Nosocomial Infections screened available literature and integrated available knowledge on infection prevention and C. auris epidemiology and biology to enable optimal containment. Relevant recommendations developed during this process are summarized in this guidance document, intended to assist in management of C. auris transmission and potential outbreak situations. Rapid and effective measures to contain C. auris spread require a multidisciplinary approach that includes clinical specialists of the affected unit, nursing staff, hospital hygiene, diagnostic microbiology, cleaning staff, hospital management and experts in diagnostic mycology / fungal infections. Action should be initiated in a step-wise process and relevant interventions differ between management of singular C. auris colonized / infected patients and detection of potential C. auris transmission or nosocomial outbreaks. [word count 205].

Raman Imaging of Pathogenic Candida auris: Visualization of Structural Characteristics and Machine-Learning Identification

Invasive fungal infections caused by yeasts of the genus Candida carry high morbidity and cause systemic infections with high mortality rate in both immunocompetent and immunosuppressed patients. Resistance rates against antifungal drugs vary among Candida species, the most concerning specie being Candida auris, which exhibits resistance to all major classes of available antifungal drugs. The presently available identification methods for Candida species face a severe trade-off between testing speed and accuracy. Here, we propose and validate a machine-learning approach adapted to Raman spectroscopy as a rapid, precise, and labor-efficient method of clinical microbiology for C. auris identification and drug efficacy assessments. This paper demonstrates that the combination of Raman spectroscopy and machine learning analyses can provide an insightful and flexible mycology diagnostic tool, easily applicable on-site in the clinical environment.