Fungal Endocarditis: Pathophysiology, Epidemiology, Clinical Presentation, Diagnosis, and Management

Novel antifungals and treatment approaches to tackle resistance and improve outcomes of invasive fungal disease

SUMMARYFungal infections are on the rise, driven by a growing population at risk and climate change. Currently available antifungals include only five classes, and their utility and efficacy in antifungal treatment are limited by one or more of innate or acquired resistance in some fungi, poor penetration into "sequestered" sites, and agent-specific side effect which require frequent patient reassessment and monitoring. Agents with novel mechanisms, favorable pharmacokinetic (PK) profiles including good oral bioavailability, and fungicidal mechanism(s) are urgently needed. Here, we provide a comprehensive review of novel antifungal agents, with both improved known mechanisms of actions and new antifungal classes, currently in clinical development for treating invasive yeast, mold (filamentous fungi), Pneumocystis jirovecii infections, and dimorphic fungi (endemic mycoses). We further focus on inhaled antifungals and the role of immunotherapy in tackling fungal infections, and the specific PK/pharmacodynamic profiles, tissue distributions as well as drug-drug interactions of novel antifungals. Finally, we review antifungal resistance mechanisms, the role of use of antifungal pesticides in agriculture as drivers of drug resistance, and detail detection methods for antifungal resistance.

Universal digital high-resolution melting for the detection of pulmonary mold infections

Invasive mold infections (IMIs) are associated with high morbidity, particularly in immunocompromised patients, with mortality rates between 40% and 80%. Early initiation of appropriate antifungal therapy can substantially improve outcomes, yet early diagnosis remains difficult to establish and often requires multidisciplinary teams evaluating clinical and radiological findings plus supportive mycological findings. Universal digital high-resolution melting (U-dHRM) analysis may enable rapid and robust diagnoses of IMI. A universal fungal assay was developed for U-dHRM and used to generate a database of melt curve signatures for 19 clinically relevant fungal pathogens. A machine learning algorithm (ML) was trained to automatically classify these pathogen curves and detect novel melt curves. Performance was assessed on 73 clinical bronchoalveolar lavage samples from patients suspected of IMI. Novel curves were identified by micropipetting U-dHRM reactions and Sanger sequencing amplicons. U-dHRM achieved 97% overall fungal organism identification accuracy and a turnaround time of ~4 hrs. U-dHRM detected pathogenic molds (Aspergillus, Mucorales, Lomentospora, and Fusarium) in 73% of 30 samples classified as IMI, including mixed infections. Specificity was optimized by requiring the number of pathogenic mold curves detected in a sample to be >8 and a sample volume to be 1 mL, which resulted in 100% specificity in 21 at-risk patients without IMI. U-dHRM showed promise as a separate or combination diagnostic approach to standard mycological tests. U-dHRM's speed, ability to simultaneously identify and quantify clinically relevant mold pathogens in polymicrobial samples, and detect emerging opportunistic pathogens may aid treatment decisions, improving patient outcomes.

IMPORTANCE

Improvements in diagnostics for invasive mold infections are urgently needed. This work presents a new molecular detection approach that addresses technical and workflow challenges to provide fast pathogen detection, identification, and quantification that could inform treatment to improve patient outcomes.

Uncommon pathogens causing infective endocarditis

Infective endocarditis is caused by a wide range of aetiological agents. The microbiology, epidemiology, and treatment of this disease have changed considerably in the last two decades. Staphylococci and streptococci are known to be the classical causative agents; however, blood culture-negative endocarditis caused by fastidious and slow-growing organisms is now common. The list of uncommon pathogens causing endocarditis has expanded in recent years. This is a narrative literature review of the aetiological agents of endocarditis that are rarely encountered in clinical practice, their epidemiology, the characteristics of these pathogens, the clinical presentations of the cases, and their management.

Invasive candidiasis

Invasive candidiasis is an important fungal disease caused by Candida albicans and, increasingly, non-albicans Candida pathogens. Invasive Candida infections originate most frequently from endogenous human reservoirs and are triggered by impaired host defences. Signs and symptoms of invasive candidiasis are non-specific; candidaemia is the most diagnosed manifestation, with disseminated candidiasis affecting single or multiple organs. Diagnosis poses many challenges, and conventional culture techniques are frequently supplemented by non-culture-based assays. The attributable mortality from candidaemia and disseminated infections is ~30%. Fluconazole resistance is a concern for Nakaseomyces glabratus, Candida parapsilosis, and Candida auris and less so in Candida tropicalis infection; acquired echinocandin resistance remains uncommon. The epidemiology of invasive candidiasis varies in different geographical areas and within various patient populations. Risk factors include intensive care unit stay, central venous catheter use, broad-spectrum antibiotics use, abdominal surgery and immune suppression. Early antifungal treatment and central venous catheter removal form the cornerstones to decrease mortality. The landscape of novel therapeutics is growing; however, the application of new drugs requires careful selection of eligible patients as the spectrum of activity is limited to a few fungal species. Unanswered questions and knowledge gaps define future research priorities and a personalized approach to diagnosis and treatment of invasive candidiasis is of paramount importance.

Synthesis and antifungal evaluation against Candida spp. of the (E)-3-(furan-2-yl)acrylic acid

Infections of fungal origin are mainly caused by Candida spp. Some species, such as C. albicans, C. glabrata, C. parapsilosis, and C. tropicalis, stand out as promoters of diseases in humans. This study evaluated the synthesis and antifungal effects of (E)-3-(furan-2-yl)acrylic acid. The synthesis of the compound showed a yield of 88%, considered high. The minimum inhibitory concentration of the synthetic compound, amphotericin B, and fluconazole isolated against four Candida species ranged from 64 to 512 μg/mL, 1 to 2 μg/mL, and 32 to 256 μg/mL, respectively. The synergistic effect of the test compound was observed when associated with amphotericin B against C. albicans and C. tropicalis, with no antagonism between the substances against any of the strains tested. The potential drug promoted morphological changes in C. albicans, decreasing the amount of resistance and virulence, and reproduction structures, such as the formation of pseudohyphae, blastoconidia, and chlamydospores. Furthermore, it was also possible to identify the fungistatic profile of the test substance by studying the growth kinetics of C. albicans. Finally, it was observed that the test compound stimulated ergosterol biosynthesis by the yeast, probably by activating microbial resistance responses.

Late Recurrence of Prosthetic Valve Endocarditis Due to Candida albicans

BACKGROUND Candida prosthetic valve endocarditis is a rare disease that is increasing in incidence with the rising rates of fungemia and increased use of intracardiac devices. Chronic antifungal prophylaxis is used after primary treatment to prevent recurrence, but the optimal duration of prophylaxis is currently unknown. This case report is of a woman with a history of mitral valve replacement due to Candida endocarditis presenting 2 years later with prosthetic valve and native aortic valve Candida albicans endocarditis. CASE REPORT A 32-year-old woman with a history of intravenous drug abuse, Staphylococcus and Candida endocarditis, and 2 mitral valve replacements 2 years ago on long-term oral fluconazole presented with fevers, weight loss, and dyspnea. She had stopped taking her oral antifungals prior to presentation. She was found to have vegetations on her prosthetic mitral valve and on her native aortic valve. She was started on ceftriaxone, vancomycin, and micafungin, and blood cultures grew C. albicans. She also developed a C. albicans metatarsal abscess and a splenic infarct. She underwent redo mitral valve replacement and aortic valve debridement successfully and was continued on intravenous micafungin for 8 weeks. CONCLUSIONS This case highlights the association between prosthetic valve endocarditis, intravenous drug abuse, and opportunistic fungal infections. Lifelong oral fluconazole can be considered for all patients with C. albicans prosthetic valve endocarditis, especially in the setting of the presence of other risk factors, such as intravenous drug abuse, as demonstrated in our case. Further studies are needed to determine differences in outcomes.

First case report of Candida guilliermondii native left-sided valve endocarditis

Endocarditis, a life-threatening inflammation of the endocardium, is incited by bacteria, fungi, or other pathogenic microorganisms. Fungal endocarditis closely mirrors bacterial endocarditis in clinical signs and symptoms, leading to potential misdiagnoses. Here, we unveil the inaugural confirmed instance of native left-sided valve endocarditis attributed to Candida guilliermondii. Diagnosis was substantiated through valvular biopsies, blood and vegetative cultures. Treatment encompassed surgical excision of vegetations along with a six-week regimen of fluconazole administration (12 mg/kg/day), followed by 4 years of meticulous monitoring, resulting in sustained patient recovery.

Social determinants of health as drivers of fungal disease

Disparities in social determinants of health (SDOH) play a significant role in causing health inequities globally. The physical environment, including housing and workplace environment, can increase the prevalence and spread of fungal infections. A number of professions are associated with increased fungal infection risk and are associated with low pay, which may be linked to crowded and sub-optimal living conditions, exposure to fungal organisms, lack of access to quality health care, and risk for fungal infection. Those involved and displaced from areas of armed conflict have an increased risk of invasive fungal infections. Lastly, a number of fungal plant pathogens already threaten food security, which will become more problematic with global climate change. Taken together, disparities in SDOH are associated with increased risk for contracting fungal infections. More emphasis needs to be placed on systematic approaches to better understand the impact and reducing the health inequities associated with these disparities.

Pharmacokinetic and pharmacodynamic considerations for antifungal therapy optimisation in the treatment of intra-abdominal candidiasis

Intra-abdominal candidiasis (IAC) is one of the most common of invasive candidiasis observed in critically ill patients. It is associated with high mortality, with up to 50% of deaths attributable to delays in source control and/or the introduction of antifungal therapy. Currently, there is no comprehensive guidance on optimising antifungal dosing in the treatment of IAC among the critically ill. However, this form of abdominal sepsis presents specific pharmacokinetic (PK) alterations and pharmacodynamic (PD) challenges that risk suboptimal antifungal exposure at the site of infection in critically ill patients. This review aims to describe the peculiarities of IAC from both PK and PD perspectives, advocating an individualized approach to antifungal dosing. Additionally, all current PK/PD studies relating to IAC are reviewed in terms of strength and limitations, so that core elements for the basis of future research can be provided.

Universal Digital High Resolution Melt for the detection of pulmonary mold infections

Background

Invasive mold infections (IMIs) such as aspergillosis, mucormycosis, fusariosis, and lomentosporiosis are associated with high morbidity and mortality, particularly in immunocompromised patients, with mortality rates as high as 40% to 80%. Outcomes could be substantially improved with early initiation of appropriate antifungal therapy, yet early diagnosis remains difficult to establish and often requires multidisciplinary teams evaluating clinical and radiological findings plus supportive mycological findings. Universal digital high resolution melting analysis (U-dHRM) may enable rapid and robust diagnosis of IMI. This technology aims to accomplish timely pathogen detection at the single genome level by conducting broad-based amplification of microbial barcoding genes in a digital polymerase chain reaction (dPCR) format, followed by high-resolution melting of the DNA amplicons in each digital reaction to generate organism-specific melt curve signatures that are identified by machine learning.

Methods

A universal fungal assay was developed for U-dHRM and used to generate a database of melt curve signatures for 19 clinically relevant fungal pathogens. A machine learning algorithm (ML) was trained to automatically classify these 19 fungal melt curves and detect novel melt curves. Performance was assessed on 73 clinical bronchoalveolar lavage (BAL) samples from patients suspected of IMI. Novel curves were identified by micropipetting U-dHRM reactions and Sanger sequencing amplicons.

Results

U-dHRM achieved an average of 97% fungal organism identification accuracy and a turn-around-time of 4hrs. Pathogenic molds (Aspergillus, Mucorales, Lomentospora and Fusarium) were detected by U-dHRM in 73% of BALF samples suspected of IMI. Mixtures of pathogenic molds were detected in 19%. U-dHRM demonstrated good sensitivity for IMI, as defined by current diagnostic criteria, when clinical findings were also considered.

Conclusions

U-dHRM showed promising performance as a separate or combination diagnostic approach to standard mycological tests. The speed of U-dHRM and its ability to simultaneously identify and quantify clinically relevant mold pathogens in polymicrobial samples as well as detect emerging opportunistic pathogens may provide information that could aid in treatment decisions and improve patient outcomes.