Catechol thwarts virulent dimorphism in Candida albicans and potentiates the antifungal efficacy of azoles and polyenes

Cetyltrimethylammonium Chloride (CTAC) and Its Formulated Mouthwash Reduce the Infectivity of Streptococcus mutans and Candida albicans in Mono and Dual State

Early childhood caries (ECC), a severe form of dental caries, is exacerbated by the synergistic interaction between Streptococcus mutans and Candida albicans, leading to greater disease severity than their individual effects. This underscores the need for more targeted and potent therapeutic alternatives. Given the promising anti-infective properties of quaternary ammonium surfactants (QAS), this study explores the microbicidal properties of one such QAS, cetyltrimethylammonium chloride (CTAC), against both individual- and dual-species cultures of S. mutans and C. albicans for effective ECC treatment. Initially, the minimal inhibitory concentrations (MICs) of CTAC were determined to range from 4 to 8 µg/mL against S. mutans, C. albicans, and dual-species cultures. Time-kill kinetics, assessed via spot assays and spectrometry, demonstrated that CTAC completely eradicated both individual- and dual-species cultures within 30 min of exposure. Furthermore, at sub-MIC concentrations, CTAC effectively reduced biofilm formation and virulence traits in S. mutans (including acidogenicity and aciduricity) and C. albicans (including yeast-to-hyphal transition and filamentation). To explore therapeutic application, a mouthwash containing CTAC was formulated. The results showed that the formulated CTAC mouthwash was as effective at eradicating pathogens as a commercially available mouthwash containing 0.075% cetylpyridinium chloride (CPC). Moreover, the CTAC mouthwash maintained stable physicochemical characteristics and antimicrobial activity over 4 weeks. It exhibited rapid killing activity against pathogens, achieving efficacy within just 2 min of exposure. Fluorescence microscopy and SEM micrographs confirmed the strong biofilm eradication potential of the CTAC mouthwash. The non-toxic nature of the formulated mouthwash was validated using human buccal epithelial cells, and in vivo studies further demonstrated that CTAC mouthwash significantly reduced bacterial and fungal loads in Galleria mellonella. Overall, the findings of this study highlight the potential application of QAS-CTAC in the treatment of ECC.

Anticariogenic activity of marine brown algae Padina boergesenii and its active components towards Streptococcus mutans

Streptococcus mutans is a well-recognized bacterium that plays a predominant role in the progression of dental caries. Its pathogenicity is linked to several key characteristics, including the ability to produce organic acids (acidogenicity), thrive in low pH environments (aciduricity), synthesize exopolysaccharides (EPS) via glucosyltransferases, and form retentive biofilms. The treatment of dental caries with conventional antibiotics is often ineffective due to the bacterium's capacity to form recalcitrant biofilms. To address these challenges, strategies that specifically target the pathogen's virulence without affecting its viability have emerged as promising alternatives. In this context, we investigated the anticariogenic properties of the methanolic extract of Padina boergesenii (MEPB). MEPB demonstrated substantial, dose-dependent antibiofilm activity, with a maximum inhibition of 93% at 128 μg/mL, without compromising the viability of S. mutans. Anti-virulence assays using sub-MIC (minimum inhibitory concentration) levels of MEPB showed significant reductions in key virulence factors: 75% reduction in sucrose-dependent adherence, 65% reduction in sucrose-independent adherence, along with notable decreases in acid production, acid tolerance, and water-insoluble (85%) and water-soluble (52%) glucan synthesis. Additionally, MEPB significantly reduced cell surface hydrophobicity (55%) and extracellular DNA (eDNA) production (64%). qPCR analysis corroborated these in vitro findings, revealing that MEPB suppresses the expression of genes involved in S. mutans virulence, particularly genes related to EPS synthesis (gtfB, gtfC & gtfD) biofilm formation(gbpB & gbpC) and two-component regulatory system (vicR) were downregulated. Toxicity testing on human buccal epithelial cells confirmed the non-toxic nature of MEPB, suggesting its safety for potential therapeutic use. Furthermore, GC-MS/MS analysis identified palmitic acid, myristic acid, and stearic acid as the major active constituents of the MEPB extract. Subsequent biofilm inhibitory assays confirmed the potent antibiofilm efficacy of these compounds: palmitic acid (85%), myristic acid (72%) and stearic acid (83%). In conclusion, this study identifies P. boergesenii and its active biomolecules as potential anticariogenic agents, offering an alternative approach to combat dental caries by targeting bacterial virulence mechanisms rather than viability.

Global research trends and hotspots on human intestinal fungi and health: a bibliometric visualization study

Background

This article employs bibliometric methods and visual maps to delineate the research background, collaborative relationships, hotspots, and trends in the study of gut fungi in human diseases and health.

Methods

Publications related to human gut fungi were retrieved from the Web of Science Core Collection. VOSviewer, CiteSpace, R software and Microsoft Excel were employed to generate visual representations illustrating the contributions made by countries/regions, authors, organizations, and journals. Employing VOSviewer and CiteSpace, we conducted a comprehensive analysis of the retrieved publications, revealing underlying tendencies, research hotspots, and intricate knowledge networks.

Results

This study analyzed a total of 3,954 publications. The United States ranks first in the number of published papers and has the highest number of citations and h-index. Mostafa S Elshahed is the most prolific author. The University of California System is the institution that published the most papers. Frontiers In Microbiology is the journal with the largest number of publications. Three frequently co-cited references have experienced a citation burst lasting until 2024.

Conclusion

Advancements in sequencing technologies have intensified research into human gut fungi and their health implications, shifting the research focus from gut fungal infections towards microbiome science. Inflammatory bowel diseases and Candida albicans have emerged as pivotal areas of interest in this endeavor. Through this study, we have gained a deeper insight into global trends and frontier hotspots within this field, thereby enhancing our understanding of the intricate relationship between gut fungi and human health.

Synergistic anti-virulence efficacy of citral and carvacrol against mixed vaginitis causing Candida albicans and Gardnerella vaginalis: An in vitro and in vivo study

Mixed vaginitis due to bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC) is the most prevalent form and presents a significant therapeutic challenge globally. Since, the administration of monotherapy leads to subsequent recurrent infections, synergistic therapy that completely eradicates both pathogens is of dire need to manage mixed vaginities scenario and to prevent its recurrence. The current investigation was focused on exploring the synergistic inhibitory efficacy of phytochemicals against the virulence traits of individual and mixed species of C. albicans and G. vaginalis in vitro and in vivo (Galleria mellonella). Out of five phytochemicals (carvacrol, thymol, cinnamaldehyde, eugenol, and borneol) screened for synergism with citral [(Ct) as the prime molecule owing to its myriad therapeutic potential], carvacrol (Ca) in combination with citral exhibited promising synergistic effect. Time-kill kinetics and one-minute contact-killing assays demonstrated the phenomenal microbicidal effect of Ct-Ca combination against both mono and dual-species within 30 min and one-minute time intervals, respectively. Furthermore, the sub-CMICs (synergistic combinatorial MIC) of Ct-Ca have significantly eradicated the mature biofilms and remarkably reduced the virulence attributes of both C. albicans and G. vaginalis (viz., yeast to hyphae transition, filamentation, protease production, and hydrophobicity index), in single and dual species states. The non-toxic nature of Ct-Ca combination was authenticated using in vitro (human erythrocyte cells) and in vivo (Galleria mellonella) models. In addition, the in vivo efficacy evaluation and subsequent histopathological investigation was done using the invertebrate model system G. mellonella, which further ascertained the effectiveness of Ct-Ca combination in fighting off the infection caused by individual and mixed species of C. albicans and G. vaginalis. Concomitantly, the current work is the first of its kind to delineate the in vitro interaction of C. albicans and G. vaginalis mixed species at their growth and biofilm states, together emphasizes the promising therapeutic potential of acclaimed phytochemicals as combinatorial synergistic therapy against mixed vaginitis.

A pipeline for rapidly evaluating activity and inferring mechanisms of action of prospective antifungal compounds

BACKGROUND

Fungal phytopathogens are a significant threat to crops and food security, and there is a constant need to develop safe and effective compounds that antagonize them. In-planta assays are complex and tedious and are thus not suitable for initial high-throughput screening of new candidate antifungal compounds. We propose an in vitro screening pipeline that integrates five rapid quantitative and qualitative methods to estimate the efficacy and mode of action of prospective antifungal compounds.

RESULTS

The pipeline was evaluated using five documented antifungal compounds (benomyl, catechol, cycloheximide, 2,4-diacetylphloroglucinol, and phenylacetic acid) that have different modes of action and efficacy, against the model soilborne fungal pathogen Fusarium oxysporum f. sp. radicis cucumerinum. We initially evaluated the five compounds' ability to inhibit fungal growth and metabolic activity using green fluorescent protein (GFP)-labeled F. oxysporum and PrestoBlue staining, respectively, in multiwell plate assays. We tested the compounds' inhibition of both conidial germination and hyphal elongation. We then employed FUN-1 and SYTO9/propidium iodide staining, coupled to confocal microscopy, to differentiate between fungal growth inhibition and death at the cellular level. Finally, using a reactive oxygen species (ROS)-detection assay, we were able to quantify ROS production in response to compound application.

CONCLUSIONS

Collectively, the proposed pipeline provides a wide array of quantitative and qualitative data on the tested compounds that can help pinpoint promising novel compounds; these can then be evaluated more vigorously using in planta screening assays. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Deciphering the Mechanism of MRSA Targeting Copper(II) Complexes of NN2 Pincer-Type Ligands

WHO lists AMR as one of the top ten global public health issues. Therefore, constant effort is needed to develop more efficient antimicrobial drugs. As a result, earth-abundant transition-metal complexes have emerged as an excellent solution. In this regard, new aminoquinoline-based copper(II) pincer complexes 1-3 were designed, synthesized, and characterized by modern spectroscopic techniques. It is worth mentioning that, at the highest concentration (1024 μg/mL) of complexes (1-3), the hemolysis was found to be <15%, implying their less toxicity. Further, the complexes effectively interfered with the growth of Gram positive MRSA and the fungus Candida albicans. Among them, complex 2 was promising (MIC = 16 μg/mL) against MRSA, which was better than the known antibacterial drug kanamycin (64 μg/mL) under identical conditions. The Alamar blue cell viability test and the MBC/MFC identified by spot assay were in accordance with MIC values. Moreover, the insilico studies explained the most probable mechanism of action as inhibition of cell wall biosynthesis and dysfunction of antibiotic sensing proteins. Similarly, the antifungal action might be due to the cell surface adhesion protein dysfunction by the complexes. Furthermore, we are expecting to draw these compounds for clinical applications.

Azole potentiation in Candida species

Fungal infections are rising, with over 1.5 billion cases and more than 1 million deaths recorded each year. Among these, Candida infections are frequent in at-risk populations and the rapid development of drug resistance and tolerance contributes to their clinical persistence. Few antifungal drugs are available, and their efficacy is declining due to the environmental overuse and the expansion of multidrug-resistant species. One way to prolong their utility is by applying them in combination therapy. Here, we highlight recently described azole potentiators belonging to different categories: natural, repurposed, or novel compounds. We showcase examples of molecules and discuss their identified or proposed mode of action. We also emphasise the challenges in azole potentiator development, compounded by the lack of animal testing, the overreliance on Candida albicans and Candida auris, as well as the limited understanding of compound efficacy.

Alteration of Cell Membrane Permeability by Cetyltrimethylammonium Chloride Induces Cell Death in Clinically Important Candida Species

The increased incidence of healthcare-related Candida infection has necessitated the use of effective disinfectants/antiseptics in healthcare settings as a preventive measure to decontaminate the hospital environment and stop the persistent colonization of the offending pathogens. Quanternary ammonium surfactants (QASs), with their promising antimicrobial efficacy, are considered as intriguing and appealing candidates for disinfectants. From this perspective, the present study investigated the antifungal efficacy and action mechanism of the QAS cetyltrimethylammonium chloride (CTAC) against three clinically important Candida species: C. albicans, C. tropicalis, and C. glabrata. CTAC exhibited phenomenal antifungal activity against all tested Candida spp., with minimum inhibitory concentrations (MIC) and minimum fungicidal concentrations (MFC) between 2 and 8 µg/mL. The time−kill kinetics of CTAC (at 2XMIC) demonstrated that an exposure time of 2 h was required to kill 99.9% of the inoculums in all tested strains. An important observation was that CTAC treatment did not influence intracellular reactive oxygen species (ROS), signifying that its phenomenal anticandidal efficacy was not mediated via oxidative stress. In addition, sorbitol supplementation increased CTAC’s MIC values against all tested Candida strains by three times (8−32 μg/mL), indicating that CTAC’s possible antifungal activity involves fungus cell membrane destruction. Interestingly, the increased fluorescence intensity of CTAC-treated cells in both propidium iodide (PI) and DAPI staining assays indicated the impairment of cell plasma membrane and nuclear membrane integrity by CTAC, respectively. Additionally, CTAC at MIC and 2XMIC was sufficient (>80%) to disrupt the mature biofilms of all tested spp., and it inhibited the yeast-to-hyphae transition at sub-MIC in C. albicans. Finally, the non-hemolytic activity of CTAC (upto 32 µg/mL) in human blood cells and HBECs signified its non-toxic nature at the investigated concentrations. Furthermore, thymol and citral, two phytocompounds, together with CTAC, showed synergistic fungicidal effectiveness against C. albicans planktonic cells. Altogether, the data of the present study appreciably broaden our understanding of the antifungal action mechanism of CTAC and support its future translation as a potential disinfectant against Candida-associated healthcare infections.

Evaluation of the Anti-Histoplasma capsulatum Activity of Indole and Nitrofuran Derivatives and Their Pharmacological Safety in Three-Dimensional Cell Cultures

Histoplasma capsulatum is a fungus that causes histoplasmosis. The increased evolution of microbial resistance and the adverse effects of current antifungals help new drugs to emerge. In this work, fifty-four nitrofurans and indoles were tested against the H. capsulatum EH-315 strain. Compounds with a minimum inhibitory concentration (MIC₉₀) equal to or lower than 7.81 µg/mL were selected to evaluate their MIC₉₀ on ATCC G217-B strain and their minimum fungicide concentration (MFC) on both strains. The quantification of membrane ergosterol, cell wall integrity, the production of reactive oxygen species, and the induction of death by necrosis–apoptosis was performed to investigate the mechanism of action of compounds 7, 11, and 32. These compounds could reduce the extracted sterol and induce necrotic cell death, similarly to itraconazole. Moreover, 7 and 11 damaged the cell wall, causing flaws in the contour (11), or changing the size and shape of the fungal cell wall (7). Furthermore, 7 and 32 induced reactive oxygen species (ROS) formation higher than 11 and control. Finally, the cytotoxicity was measured in two models of cell culture, i.e., monolayers (cells are flat) and a three-dimensional (3D) model, where they present a spheroidal conformation. Cytotoxicity assays in the 3D model showed a lower toxicity in the compounds than those performed on cell monolayers. Overall, these results suggest that derivatives of nitrofurans and indoles are promising compounds for the treatment of histoplasmosis.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.

Emerging Antifungal Targets and Strategies

Despite abundant research in the field of antifungal drug discovery, fungal infections remain a significant healthcare burden. There is an emerging need for the development of novel antifungals since those currently available are limited and do not completely provide safe and secure protection. Since the current knowledge regarding the physiology of fungal cells and the infection mechanisms is greater than ever, we have the opportunity to use this for the development of novel generations of antifungals. In this review, we selected and summarized recent studies describing agents employing different antifungal mechanisms. These mechanisms include interference with fungal resistance, including impact on the efflux pumps and heat shock protein 90. Additionally, interference with virulence factors, such as biofilms and hyphae; the impact on fungal enzymes, metabolism, mitochondria, and cell wall; and antifungal vaccines are explored. The agents investigated belong to different classes of natural or synthetic molecules with significant attention given also to plant extracts. The efficacy of these antifungals has been studied mainly in vitro with some in vivo, and clinical studies are needed. Nevertheless, there is a large quantity of products employing novel antifungal mechanisms that can be further explored for the development of new generation of antifungals.