Antimicrobials and Resistance Part II: Antifungals, Antivirals, and Antiparasitics

Bio-formulated chitosan nanoparticles enhance disease resistance against rice blast by physiomorphic, transcriptional, and microbiome modulation of rice (Oryza sativa L.)

Rice blast disease (RBD) caused by Magnaporthe oryzae, threaten food security by cutting agricultural output. Nano agrochemicals are now perceived as sustainable, cost-effective alternatives to traditional pesticides. This study investigated bioformulation of moringa chitosan nanoparticles (M-CsNPs) and their mechanisms for suppressing RBD while minimizing toxic effects on the microenvironment. M-CsNPs, sized 46 nm with semi-spherical morphology, significantly suppressed pathogen growth, integrity, and colonization at 200 mg L-1in vitro. Greenhouse tests with foliar exposure to the same concentration resulted in a substantial 77.7 % reduction in RBD, enhancing antioxidant enzyme activity and plant health. Furthermore, M-CsNPs improved photosynthesis, gas exchange, and the nutritional profile of diseased rice plants. RNA-seq analysis highlighted upregulated defense-related genes in treated rice plants. Metagenomic study showcased reshaping of the rice microbiome, reducing Magnaporthe abundance by 93.5 %. Both healthy and diseased rice plants showed increased microbial diversity, particularly favoring specific beneficial species Thiobacillus, Nitrospira, Nocardioides, and Sphingomicrobium in the rhizosphere and Azonexus, Agarivorans, and Bradyrhizobium in the phyllosphere. This comprehensive study unravels the diverse mechanisms by which M-CsNPs interact with plants and pathogens, curbing M. oryzae damage, promoting plant growth, and modulating the rice microbiome. It underscores the significant potential for effective plant disease management.

Combination oral antifungal therapy for paediatric fungal infection: An option to improve efficacy and overcome clinical resistance

There is increasing evidence of clinically resistant cutaneous fungal infections. The use of combination oral antifungals is described in adults but not in paediatric patients. We present seven paediatric cases of clinically resistant fungal infections treated successfully with combination oral antifungal therapy after inadequate response to a single agent.

Evaluation of proline-rich antimicrobial peptides as potential lead structures for novel antimycotics against Cryptococcus neoformans

Background

Cryptococcosis and cryptococcal meningitis, caused by Cryptococcus neoformans infections, lead to approximately 180,000 deaths per year, primarily in developing countries. Individuals with compromised immune systems, e.g., due to HIV infection (AIDS) or chemotherapy, are particularly vulnerable. Conventional treatment options are often limited and can cause severe side effects. Therefore, this study aimed to investigate the antifungal effect of insect-derived proline-rich antimicrobial peptides (PrAMPs) against C. neoformans. These peptides are known for their low toxicity and their high efficacy in murine infection models, making them a promising alternative for treatment.

Results

A preliminary screening of the minimal inhibitory concentrations (MICs) of 20 AMPs, including the well-known PrAMPs Onc112, Api137, and Chex1Arg20 as well as the cathelicidin CRAMP against the C. neoformans strains 1841, H99, and KN99α revealed promising results, with MICs as low as 1.6 μmol/L. Subsequent investigations of selected peptides, determining their influence on fungal colony-forming units, confirmed their strong activity. The antifungal activity was affected by factors such as peptide net charge and sequence, with stronger effects at higher net charges probably due to better intracellular uptake confirmed by confocal laser scanning microscopy. Inactive scrambled peptides suggest a specific intracellular target, although scanning electron microscopy showed that PrAMPs also damaged the cell exterior for a low proportion of the cells. Possible pore formation could facilitate entry into the cytosol.

Treatment of onychomycosis in an era of antifungal resistance: Role for antifungal stewardship and topical antifungal agents

A growing body of literature has marked the emergence and spread of antifungal resistance among species of Trichophyton, the most prevalent cause of toenail and fingernail onychomycosis in the United States and Europe. We review published data on rates of oral antifungal resistance among Trichophyton species; causes of antifungal resistance and methods to counteract it; and in vitro data on the role of topical antifungals in the treatment of onychomycosis. Antifungal resistance among species of Trichophyton against terbinafine and itraconazole-the two most common oral treatments for onychomycosis and other superficial fungal infections caused by dermatophytes-has been detected around the globe. Fungal adaptations, patient characteristics (e.g., immunocompromised status; drug-drug interactions), and empirical diagnostic and treatment patterns may contribute to reduced antifungal efficacy and the development of antifungal resistance. Antifungal stewardship efforts aim to ensure proper antifungal use to limit antifungal resistance and improve clinical outcomes. In the treatment of onychomycosis, critical aspects of antifungal stewardship include proper identification of the fungal infection prior to initiation of treatment and improvements in physician and patient education. Topical ciclopirox, efinaconazole and tavaborole, delivered either alone or in combination with oral antifungals, have demonstrated efficacy in vitro against susceptible and/or resistant isolates of Trichophyton species, with low potential for development of antifungal resistance. Additional real-world long-term data are needed to monitor global rates of antifungal resistance and assess the efficacy of oral and topical antifungals, alone or in combination, in counteracting antifungal resistance in the treatment of onychomycosis.

Reliable and rapid identification of terbinafine resistance in dermatophytic nail and skin infections

BACKGROUND

Fungal infections are the most frequent dermatoses. The gold standard treatment for dermatophytosis is the squalene epoxidase (SQLE) inhibitor terbinafine. Pathogenic dermatophytes resistant to terbinafine are an emerging global threat. Here, we determine the proportion of resistant fungal skin infections, analyse the molecular mechanisms of terbinafine resistance, and validate a method for its reliable rapid identification.

METHODS

Between 2013 and 2021, we screened 5634 consecutively isolated Trichophyton for antifungal resistance determined by hyphal growth on Sabouraud dextrose agar medium containing 0.2 μg/mL terbinafine. All Trichophyton isolates with preserved growth capacity in the presence of terbinafine underwent SQLE sequencing. Minimum inhibitory concentrations (MICs) were determined by the broth microdilution method.

RESULTS

Over an 8-year period, the proportion of fungal skin infections resistant to terbinafine increased from 0.63% in 2013 to 1.3% in 2021. Our routine phenotypic in vitro screening analysis identified 0.83% (n = 47/5634) of Trichophyton strains with in vitro terbinafine resistance. Molecular screening detected a mutation in the SQLE in all cases. Mutations L393F, L393S, F397L, F397I, F397V, Q408K, F415I, F415S, F415V, H440Y, or A398 A399 G400 deletion were detected in Trichophyton rubrum. Mutations L393F and F397L were the most frequent. In contrast, all mutations detected in T. mentagrophytes/T. interdigitale complex strains were F397L, except for one strain with L393S. All 47 strains featured significantly higher MICs than terbinafine-sensitive controls. The mutation-related range of MICs varied between 0.004 and 16.0 μg/mL, with MIC as low as 0.015 μg/mL conferring clinical resistance to standard terbinafine dosing.

CONCLUSIONS

Based on our data, we propose MIC of 0.015 μg/mL as a minimum breakpoint for predicting clinically relevant terbinafine treatment failure to standard oral dosing for dermatophyte infections. We further propose growth on Sabouraud dextrose agar medium containing 0.2 μg/mL terbinafine and SQLE sequencing as fungal sporulation-independent methods for rapid and reliable detection of terbinafine resistance.

Autophagy Alters the Susceptibility of Candida albicans Biofilms to Antifungal Agents

Candida albicans (C. albicans) reigns as a major cause of clinical candidiasis. C. albicans biofilms are known to increase resistance to antifungal agents, making biofilm-related infections particularly challenging to treat. Drug resistance is of particular concern due to the spread of multidrug-resistant fungal pathogens, while autophagy is crucial for the maintenance of cellular homeostasis. Therefore, this study aimed to investigate the effects of an activator and an inhibitor of autophagy on the susceptibility of C. albicans biofilms to antifungal agents and the related mechanisms. The susceptibility of C. albicans biofilms to different antifungal agents after treatment with or without the autophagy activator or inhibitor was evaluated using XTT assay. Alkaline phosphatase (ALP) activity and reactive oxygen species (ROS) level, as well as the expression of ROS-related and autophagy-related genes, were examined to evaluate the autophagic activity of C. albicans biofilms when treated with antifungal agents. The autophagosomes were observed by transmission electron microscopy (TEM). The susceptibility of C. albicans biofilms to antifungal agents changed when autophagy changed. The ALP activity and ROS level of C. albicans biofilms increased with the treatment of antifungal agents, and autophagosomes could be observed in C. albicans biofilms. Autophagy was involved in the susceptibility of C. albicans biofilms to antifungal agents.

Cyclic Peptides with Antifungal Properties Derived from Bacteria, Fungi, Plants, and Synthetic Sources

Fungal infections remain a significant concern for human health. The emergence of microbial resistance, the improper use of antimicrobial drugs, and the need for fewer toxic antifungal treatments in immunocompromised patients have sparked substantial interest in antifungal research. Cyclic peptides, classified as antifungal peptides, have been in development as potential antifungal agents since 1948. In recent years, there has been growing attention from the scientific community to explore cyclic peptides as a promising strategy for combating antifungal infections caused by pathogenic fungi. The identification of antifungal cyclic peptides from various sources has been possible due to the widespread interest in peptide research in recent decades. It is increasingly important to evaluate narrow- to broad-spectrum antifungal activity and the mode of action of synthetic and natural cyclic peptides for both synthesized and extracted peptides. This short review aims to highlight some of the antifungal cyclic peptides isolated from bacteria, fungi, and plants. This brief review is not intended to present an exhaustive catalog of all known antifungal cyclic peptides but rather seeks to showcase selected cyclic peptides with antifungal properties that have been isolated from bacteria, fungi, plants, and synthetic sources. The addition of commercially available cyclic antifungal peptides serves to corroborate the notion that cyclic peptides can serve as a valuable source for the development of antifungal drugs. Additionally, this review discusses the potential future of utilizing combinations of antifungal peptides from different sources. The review underscores the need for the further exploration of the novel antifungal therapeutic applications of these abundant and diverse cyclic peptides.

Photodynamic therapy mediated by a red LED and methylene blue inactivates resistant Leishmania amazonensis

Cutaneous leishmaniasis is a neglected parasitic disease that leads to destructive lesions. The emergence of drug resistance has been a global concern over the past years. Photodynamic therapy (PDT) mediated by a red LED and methylene blue (MB) involves the overproduction of oxidative stress, which oxidizes several cellular biomolecules and prevents the selection of resistant strains. Herein, we investigated the potential of PDT mediated by MB against wild-type and miltefosine-resistant strains of Leishmania amazonensis. As a result, both strains were susceptible to PDT, thus encouraging us to seek the best conditions to overcome the drug resistance problem in cutaneous leishmaniasis.

Pediatric Tinea Capitis: A Retrospective Cohort Study from 2010 to 2021

Pediatric tinea capitis displays a wide range of prevalence, with significant variability among populations. We retrospectively extracted the medical records of 456 pediatric patients diagnosed with tinea capitis during the years 2010–2021, from the dermatology outpatient clinics in two tertiary medical centers. Three species were isolated in 90% of patients: T. tonsurans, M. canis, and T. violaceum. While T. tonsurans presented a six-fold increase in incidence during the years 2019–2021, M. canis maintained stable incidence rates. Furthermore, terbinafine was the most efficient antifungal agent against T. tonsurans, achieving complete clinical clearance in 95% of patients, as compared to fluconazole (68%) and griseofulvin (38%) (p < 0.001). The mycological cure was recorded in 61/90 (68%) of patients with available data, at an average of 10 weeks. For patients with M. canis, griseofulvin and fluconazole were equally efficient (73% and 66%, respectively) (p = 0.44). Kerion was described in 36% and 14% of patients with T. tonsurans and M. canis, respectively, (p < 0.001). In conclusion, since 2019, there has been a significant increase in the prevalence of T. tonsurans, establishing this pathogen as the most common cause for tinea capitis in our population. Our data suggest that terbinafine is effective and presents high cure rates for tinea capitis in the pediatric population.

Current scenario and future applicability of antivirals against herpes zoster

Herpes zoster (HZ) is a common disease in the aging population and immunocompromised individuals, with a lifetime risk of 20%-30% that increases with age. HZ is caused by reactivation of the varicella-zoster virus (VZV), which remains latent in the spinal dorsal root ganglia and cranial sensory ganglia after resolution of the primary VZV infection. The main focus of HZ management is rapid recovery from VZV infection as well as the reduction and prevention of zoster-associated pain (ZAP) and postherpetic neuralgia (PHN). The use of antivirals against VZV is essential in the treatment of HZ. However, limited antivirals are only licensed clinically for the treatment of HZ, including acyclovir, valacyclovir, famciclovir, brivudine, and amenamevir. Fortunately, some new antivirals against different types of Herpesviridae have been investigated and suggested as novel drugs against VZV. Therefore, this review focuses on discussing the difference in efficacy and safety in the currently licensed antivirals for the treatment of HZ, the applicability of future novel antivirals against VZV, and the preventive or therapeutic effects of these antivirals on ZAP or PHN.

Antioxidant, Cytotoxic, and DNA Damage Protection Activities of Endophytic Fungus Pestalotiopsis neglecta Isolated from Ziziphus spina-christi Medicinal Plant

Fungal endophytes are friendly microorganisms that colonize plants and are important in the interactions between plants and their environment. They generate valuable secondary metabolites that are valuable to both plants and humans. Endophytic fungi with bioactivities were isolated from the leaves of the medicinal plant Ziziphus spina-christi. An efficient isolate was selected and identified as Pestalotiopsis neglecta based on nucleotide sequencing of the internal transcribed spacer region (ITS 1-5.8S-ITS 2) of the 18S rRNA gene (NCBI accession number OP529850); the 564 bp had 99 to 100% similarity with P. neglecta MH860161.1, AY682935.1, KP689121.1, and MG572407.1, according to the BLASTn analysis, following preliminary phytochemical and antifungal screening. The biological activities of this fungus' crude ethyl acetate (EtOAc) extract were assessed. With an efficient radical scavenging activity against 2,2'-diphenyl-1-picrylhydrazyl and an IC₅₀ value of 36.6 µg mL^-1, P. neglecta extract has shown its potential as an antioxidant. Moreover, it displayed notable cytotoxic effects against MCF-7 (breast carcinoma, IC₅₀ = 22.4 µg mL^-1), HeLa (cervical carcinoma, IC₅₀ = 28.9 µg mL^-1) and HepG-2 (liver carcinoma, IC₅₀ = 28.9 µg mL^-1). At 10 µg mL^-1, EtOAc demonstrated significant DNA protection against hydroxyl radical-induced damage. Based on FT-IR and GC-MS spectral analysis, it was detected that the EtOAc of P. neglecta product contains multiple bioactive functional groups. Subsequently, this validated the features of major different potent compounds; tolycaine, 1H-pyrazol, 1,3,5-trimethyl-, eugenol, 2,5-cyclohexadiene-1,4-dione, 2,6-bis(1,1-dimethyl), and bis(2-ethylhexyl) phthalate. Since these compounds are biologically relevant in various aspects, and distinct biological activities of fungal extract were acceptable in vitro, this suggests that endophytic fungus P. neglecta may be a viable source of bioactive natural products. This could be a good starting point for pharmaceutical applications.

Ring-Modified Histidine-Containing Cationic Short Peptides Exhibit Anticryptococcal Activity by Cellular Disruption

Delineation of clinical complications secondary to fungal infections, such as cryptococcal meningitis, and the concurrent emergence of multidrug resistance in large population subsets necessitates the need for the development of new classes of antifungals. Herein, we report a series of ring-modified histidine-containing short cationic peptides exhibiting anticryptococcal activity via membrane lysis. The N-1 position of histidine was benzylated, followed by iodination at the C-5 position via electrophilic iodination, and the dipeptides were obtained after coupling with tryptophan. In vitro analysis revealed that peptides Trp-His[1-(3,5-di-tert-butylbenzyl)-5-iodo]-OMe (10d, IC₅₀ = 2.20 μg/mL; MIC = 4.01 μg/mL) and Trp-His[1-(2-iodophenyl)-5-iodo)]-OMe (10o, IC₅₀ = 2.52 μg/mL; MIC = 4.59 μg/mL) exhibit promising antifungal activities against C. neoformans. When administered in combination with standard drug amphotericin B (Amp B), a significant synergism was observed, with 4- to 16-fold increase in the potencies of both peptides and Amp B. Electron microscopy analysis with SEM and TEM showed that the dipeptides primarily act via membrane disruption, leading to pore formation and causing cell lysis. After entering the cells, the peptides interact with the intracellular components as demonstrated by confocal laser scanning microscopy (CLSM).

Biocontrol of Candida albicans by Antagonistic Microorganisms and Bioactive Compounds

Candida albicans is an endogenous opportunistic pathogenic fungus that is harmless when the host system remains stable. However, C. albicans could seriously threaten human life and health when the body’s immune function declines or the normal flora is out of balance. Due to the increasing resistance of candidiasis to existing drugs, it is important to find new strategies to help treat this type of systemic fungal disease. Biological control is considered as a promising strategy which is more friendly and safer. In this review, we compare the bacteriostatic behavior of different antagonistic microorganisms (bacteria and fungi) against C. albicans. In addition, natural products with unique structures have attracted researchers’ attention. Therefore, the bioactive nature products produced by different microorganisms and their possible inhibitory mechanisms are also reviewed. The application of biological control strategies and the discovery of new compounds with antifungal activity will reduce the resistance of C. albicans, thereby promoting the development of novel diverse antifungal drugs.

Silica nanoparticles protect rice against biotic and abiotic stresses

BACKGROUND

By 2050, the world population will increase to 10 billion which urged global demand for food production to double. Plant disease and land drought will make the situation more dire, and safer and environment-friendly materials are thus considered as a new countermeasure. The rice blast fungus, Magnaporthe oryzae, causes one of the most destructive diseases of cultivated rice worldwide that seriously threatens rice production. Unfortunately, traditional breeding nor chemical approaches along control it well. Nowadays, nanotechnology stands as a new weapon against these mounting challenges and silica nanoparticles (SiO₂ NPs) have been considered as potential new safer agrochemicals recently but the systematically studies remain limited, especially in rice.

RESULTS

Salicylic acid (SA) is a key plant hormone essential for establishing plant resistance to several pathogens and its further affected a special form of induced resistance, the systemic acquired resistance (SAR), which considered as an important aspect of plant innate immunity from the locally induced disease resistance to the whole plant. Here we showed that SiO₂ NPs could stimulate plant immunity to protect rice against M. oryzae through foliar treatment that significantly decreased disease severity by nearly 70% within an appropriate concentration range. Excessive concentration of foliar treatment led to disordered intake and abnormal SA responsive genes expressions which weaken the plant resistance and even aggravated the disease. Importantly, this SA-dependent fungal resistance could achieve better results with root treatment through a SAR manner with no phytotoxicity since the orderly and moderate absorption. What's more, root treatment with SiO₂ NPs could also promote root development which was better to deal with drought.

CONCLUSIONS

Taken together, our findings not only revealed SiO₂ NPs as a potential effective and safe strategy to protect rice against biotic and abiotic stresses, but also identify root treatment for the appropriate application method since it seems not causing negative effects and even have promotion on root development.