Combating increased antifungal drug resistance in Cryptococcus, what should we do in the future?

The Contribution of Human Antimicrobial Peptides to Fungi

Various species of fungi can be detected in the environment and within the human body, many of which may become pathogenic under specific conditions, leading to various forms of fungal infections. Antimicrobial peptides (AMPs) are evolutionarily ancient components of the immune response that are quickly induced in response to infections with many pathogens in almost all tissues. There is a wide range of AMP classes in humans, many of which exhibit broad-spectrum antimicrobial function. This review provides a comprehensive overview of the mechanisms of action of AMPs, their distribution in the human body, and their antifungal activity against a range of both common and rare clinical fungal pathogens. It also discusses the current research status of promising novel antifungal strategies, highlighting the challenges that must be overcome in the development of these therapies. The hope is that antimicrobial peptides, as a class of antimicrobial agents, will soon progress through large-scale clinical trials and be implemented in clinical practice, offering new treatment options for patients suffering from infections.

Efficacy of two novel antifungal lipopeptides, AF4 and AF5 of bacillomycin D family in murine models of invasive candidiasis, cryptococcosis, and aspergillosis

Invasive fungal diseases are an important public health concern due to an increase in the at-risk population and high mortality associated with these infections. Managing invasive fungal infections poses a significant challenge given the limited antifungal options and the emergence of resistance in key fungal pathogens. Through a comprehensive approach, we evaluated the in vitro antifungal activity and the in vivo efficacy of two novel lipopeptides, AF4 and AF5 in murine models of disseminated candidiasis, cryptococcosis, and aspergillosis. Flow cytometry analysis with propidium iodide showed a dose-dependent increase in the permeability and disruption of fungal cell membranes, underscoring the membrane perturbing effects of AF4 and AF5. These observations were further substantiated by SEM analyses that showed yeast cell and hyphal deformation and leakage of cellular contents. Our in vivo investigations utilizing two doses (5 and 10 mg/kg bodyweight) of each lipopeptide and its comparison with standard antifungal therapies showed lipopeptides significantly improved the odds of mice survival in invasive candidiasis and cryptococcosis models, with a reduction in organ fungal burden by 2 to 3-log10 order. Additionally, in the disseminated aspergillosis model, treatment with 10 mg/kg of AF4 significantly improved median survival from 4 to 10 days while achieving a notable 1-log10 order reduction in organ fungal burden. Overall, our study underscores the potent and broad-spectrum antifungal activity of lipopeptides in mouse infection models, hinting at their promising therapeutic potential in invasive fungal disease.

Antifungal and antibiofilm effect of duloxetine hydrochloride against Cryptococcus neoformans and Cryptococcus gattii

Cryptococcosis is an invasive mycosis caused mainly by Cryptococcus gattii and C. neoformans and is treated with amphotericin B (AMB), fluconazole and 5-fluorocytosine. However, antifungal resistance, limited and toxic antifungal arsenal stimulate the search for therapeutic strategies such as drug repurposing. Among the repurposed drugs studied, the selective serotonin reuptake inhibitors (SSRIs) have shown activity against Cryptococcus spp. However, little is known about the antifungal effect of duloxetine hydrochloride (DH), a selective serotonin and norepinephrine reuptake inhibitor (SSNRI), against C. neoformans and C. gattii. In this study, DH inhibited the growth of several C. neoformans and C. gattii strains at concentrations ranging from 15.62 to 62.50 µg/mL. In addition, DH exhibited fungicidal activity ranging from 15.62 to 250 µg/mL. In biofilm, DH treatment reduced Cryptococcus spp. biomass at a level comparable to AMB, with a significant reduction (85%) for C. neoformans biofilms. The metabolic activity of C. neoformans and C. gattii biofilms decreased significantly (99%) after treatment with DH. Scanning electron micrographs confirmed the anti-biofilm activity of DH, as isolated cells could be observed after treatment. In conclusion, DH showed promising antifungal activity against planktonic cells and biofilms of C. neoformans and C. gattii, opening perspectives for further studies with DH in vivo.

Temporal trends in antifungal susceptibility of Cryptococcus neoformans isolates from a reference laboratory in the United States, 2011-2021

BACKGROUND

There are no established clinical breakpoints for antifungal agents against Cryptococcus species; however, epidemiological cut-off values can help distinguish wild-type (WT) isolates without any acquired resistance from non-WT strains, which may harbour resistance mechanisms.

PATIENTS/METHODS

We describe the trends of antifungal MICs and percentages of WT C. neoformans species complex (CNSC) isolates processed in our reference laboratory from November 2011 to June 2021. There were only nine isolates in 2011, thus, we included them in the year 2012 for data analysis. Clinical data is also described when available.

RESULTS

We identified 632 CNSC, the majority collected from blood (n = 301), cerebrospinal fluid (n = 230), and respiratory (n = 71) sources. The overall percentage of WT isolates for amphotericin B (AMB), 5-flucytosine, and fluconazole was 77%, 98%, and 91%, respectively. We noticed a statistically significant change in the percentage of AMB WT isolates over the years, with 98% of isolates being WT in 2012 compared to 79% in 2021 (p < .01). A similar change was not observed for other antifungal agents. Clinical data was available for 36 patients, primarily non-HIV immunocompromised patients with disseminated cryptococcosis. There were no statistically significant differences in the clinical characteristics and outcomes between patients with WT (58.3%) versus non-WT (41.7%) isolates, but we noticed higher mortality in patients infected with an AMB non-WT CNSC isolate.

CONCLUSIONS

We observed an increase in the percentage of AMB non-WT CNSC isolates in the past decade. The clinical implications of this finding warrant further evaluation in larger studies.