Natural Sources as Innovative Solutions Against Fungal Biofilms

Real-time monitoring of biofilm growth identifies andrographolide as a potent antifungal compound eradicating Candida biofilms

Candida species cause life-threatening infections with high morbidity and mortality rates and their resistance to conventional therapy is closely linked to biofilm formation. Thus, the development of new approaches to study Candida biofilms and the identification of novel therapeutic strategies could yield improved clinical outcomes. In the current study, we have set up an impedance-based in vitro system to study Candida spp. biofilms in real-time and to evaluate their sensitivity to two conventional antifungal groups used in clinical practice - azoles and echinocandins. Both fluconazole and voriconazole were unable to inhibit biofilm formation in most strains tested, while echinocandins showed biofilm inhibitory capacity at relatively low concentrations (starting from 0.625 mg/L). However, assays performed on 24 h Candida albicans and C. glabrata biofilms revealed that micafungin and caspofungin failed to eradicate mature biofilms at all tested concentrations, evidencing that once formed, Candida spp. biofilms are extremely difficult to eliminate using currently available antifungals. We then evaluated the antifungal and anti-biofilm effect of andrographolide, a natural compound isolated from the plant Andrographis paniculata with known antibiofilm activity on Gram-positive and Gram-negative bacteria. Optical density measures, impedance evaluation, CFU counts, and electron microscopy data showed that andrographolide strongly inhibits planktonic Candida spp. growth and halts Candida spp. biofilm formation in a dose-dependent manner in all tested strains. Moreover, andrographolide was capable of eliminating mature biofilms and viable cell numbers by up to 99.9% in the C. albicans and C. glabrata strains tested, suggesting its potential as a new approach to treat multi-resistant Candida spp. biofilm-related infections.

Antibiofilm Activity of Invasive Plants against Candida albicans: Focus on Baccharis halimifolia Essential Oil and Its Compounds

The extracts of five invasive plants were investigated for antifungal and antibiofilm activities against Candida albicans, C. glabrata, C. krusei, and C. parapsilosis. The antifungal activity was evaluated using the microdilution assay and the antibiofilm effect by measurement of the metabolic activity. Ethanol and ethanol-water extracts of Reynoutria japonica leaves inhibited 50 % of planktonic cells at 250 μg mL-1 and 15.6 μg mL-1 , respectively. Ethanol and ethanol-water extracts of Baccharis halimifolia inhibited >75 % of the mature biofilm of C. albicans at 500 μg mL-1 . The essential oil (EO) of B. halimifolia leaves was the most active (50 % inhibition (IC50 ) at 4 and 74 μg mL-1 against the maturation phase and 24 h old-biofilms of C. albicans, respectively). Oxygenated sesquiterpenes were the primary contents in this EO (62.02 %), with β-caryophyllene oxide as the major component (37 %). Aromadendrene oxide-(2), β-caryophyllene oxide, and (±)-β-pinene displayed significant activities against the maturation phase (IC50 =9-310 μ mol l-1 ) and preformed 24 h-biofilm (IC50 =38-630 μ mol l-1 ) of C. albicans with very low cytotoxicity for the first two compounds. C. albicans remained the most susceptible species to this EO and its components. This study highlighted for the first time the antibiofilm potential of B. halimifolia, its EO and some of its components.

Potential inhibitory activity of phytoconstituents against black fungus: In silico ADMET, molecular docking and MD simulation studies

Mucormycosis or “black fungus” has been currently observed in India, as a secondary infection in COVID-19 infected patients in the post-COVID-stage. Fungus is an uncommon opportunistic infection that affects people who have a weak immune system. In this study, 158 antifungal phytochemicals were screened using molecular docking against glucoamylase enzyme of Rhizopus oryzae to identify potential inhibitors. The docking scores of the selected phytochemicals were compared with Isomaltotriose as a positive control. Most of the compounds showed lower binding energy values than Isomaltotriose (-6.4 kcal/mol). Computational studies also revealed the strongest binding affinity of the screened phytochemicals was Dioscin (-9.4 kcal/mol). Furthermore, the binding interactions of the top ten potential phytochemicals were elucidated and further analyzed. In-silico ADME and toxicity prediction were also evaluated using SwissADME and admetSAR online servers. Compounds Piscisoflavone C, 8-O-methylaverufin and Punicalagin exhibited positive results with the Lipinski filter and drug-likeness and showed mild to moderate of toxicity. Molecular dynamics (MD) simulation (at 300 K for 100 ns) was also employed to the docked ligand-target complex to explore the stability of ligand-target complex, improve docking results, and analyze the molecular mechanisms of protein-target interactions.

Phloroglucinol and Its Derivatives: Antimicrobial Properties toward Microbial Pathogens

Phloroglucinol (PG) is a natural product isolated from plants, algae, and microorganisms. Aside from that, the number of PG derivatives has expanded due to the discovery of their potential biological roles. Aside from its diverse biological activities, PG and its derivatives have been widely utilized to treat microbial infections caused by bacteria, fungus, and viruses. The rapid emergence of antimicrobial-resistant microbial infections necessitates the chemical synthesis of numerous PG derivatives in order to meet the growing demand for drugs. This review focuses on the use of PG and its derivatives to control microbial infection and the underlying mechanism of action. Furthermore, as future perspectives, some of the various alternative strategies, such as the use of PG and its derivatives in conjugation, nanoformulation, antibiotic combination, and encapsulation, have been thoroughly discussed. This review will enable the researcher to investigate the possible antibacterial properties of PG and its derivatives, either free or in the form of various formulations.

Small molecule based anti-virulence approaches against Candida albicans infections

Fungi are considered "silent killers" due to the difficulty of, and delays in diagnosis of infections and lack of effective antifungals. This challenge is compounded by the fact that being eukaryotes, fungi share several similarities with human cellular targets, creating obstacles to drug discovery. Candida albicans, a ubiquitous microbe in the human body is well-known for its role as an opportunistic pathogen in immunosuppressed people. Significantly, C. albicans is resistant to all the three classes of antifungals that are currently clinically available. Over the past few years, a paradigm shift has been recommended in the management of C. albicans infections, wherein anti-virulence strategies are considered an alternative to the discovery of new antimycotics. Small molecules, with a molecular weight <900 Daltons, can easily permeate the cell membrane and modulate the signal transduction pathways to elicit desired virulence inhibitory actions against pathogens. This review dissects in-depth, the discoveries that have been made with small-molecule anti-virulence approaches to tackle C. albicans infections.

Efficacy of medicinal plant extracts as dental and periodontal antibiofilm agents: A systematic review of randomized clinical trials

ETHNOPHARMACOLOGICAL RELEVANCE

The presence of biofilm in oral cavity is associated with dental plaque and related diseases, including gingivitis, periodontitis and inflammatory responses. Some medicinal plants traditionally used for biofilm-associated pathologies such as Camellia sinensis (L.) Kuntze, Punica granatum L. and Lippia sidoides Cham. are currently incorporated into dosage forms as antiplaque agents.

AIMS OF THE STUDY

To present the current application of medicinal plant extracts associated in drug dosages to control microbial biofilms, with emphasis on those present in the oral cavity, especially to treat dental plaque.

MATERIALS AND METHODS

A PRISMA-compliant systematic search was conducted using the PubMed, Web of Science and Scopus databases. After the abstract and full-text analysis, the Cochrane Collaboration's tools for clinical studies was applied to assess the methodological quality of randomized clinical trials.

RESULTS

Of 964 potentially eligible studies, 47 studies met the inclusion criteria and were included in the systematic review. Camellia sinensis was the most commonly used species (8 studies), with positive results in reducing both the PI and GI in the form of mouthwash, toothpaste and gel. The Melaleuca alternifolia oil (5 studies) demonstrated low reduction in PI but important effects on GI scores. Azadirachta indica (4 studies) extracts presented efficacy similar to CHX to improve the periodontal parameters, including PI and GI. Ricinus communis oil (3 studies), despite reducing microbiological counts and GI, did not prove to be better than the hypochlorite solution, used as an alternative treatment for dentures. The main bioactive compounds described for the plant species are polyphenols, essential oils and alkaloids, most of them with identified antibiofilm activities.

CONCLUSIONS

These active species could lead to future development of safer and newer treatments for oral biofilm-associated infections. However, more studies are needed to further understand the clinical relevance of their application.

Fungal Biofilms as a Valuable Target for the Discovery of Natural Products That Cope with the Resistance of Medically Important Fungi-Latest Findings

The development of new antifungal agents that target biofilms is an urgent need. Natural products, mainly from the plant kingdom, represent an invaluable source of these entities. The present review provides an update (2017-May 2021) on the available information on essential oils, propolis, extracts from plants, algae, lichens and microorganisms, compounds from different natural sources and nanosystems containing natural products with the capacity to in vitro or in vivo modulate fungal biofilms. The search yielded 42 articles; seven involved essential oils, two Brazilian propolis, six plant extracts and one of each, extracts from lichens and algae/cyanobacteria. Twenty articles deal with the antibiofilm effect of pure natural compounds, with 10 of them including studies of the mechanism of action and five dealing with natural compounds included in nanosystems. Thirty-seven manuscripts evaluated Candida spp. biofilms and two tested Fusarium and Cryptococcus spp. Only one manuscript involved Aspergillus fumigatus. From the data presented here, it is clear that the search of natural products with activity against fungal biofilms has been a highly active area of research in recent years. However, it also reveals the necessity of deepening the studies by (i) evaluating the effect of natural products on biofilms formed by the newly emerged and worrisome health-care associated fungi, C. auris, as well as on other non-albicans Candida spp., Cryptococcus sp. and filamentous fungi; (ii) elucidating the mechanisms of action of the most active natural products; (iii) increasing the in vivo testing.

Human microbial metabolite mimicry as a strategy to expand the chemical space of potential drugs

The concept of small-molecule mimicry even of weak microbial metabolites present in rodents and humans, as a means to expand drug repertoires, is new. Hitherto, there are few proof-of-concept papers demonstrating utility of this concept. More recently, papers demonstrating mimicry of intestinal microbial metabolites could expand the drug repertoire for diseases such as inflammatory bowel disease (IBD). We opine that, as more functional metabolite-receptor pairings are discovered, small-molecule metabolite mimicry could be a significant effort in drug discovery.

Plant-Derived Substances in the Fight Against Infections Caused by Candida Species

Yeast-like fungi from the Candida genus are predominantly harmless commensals that colonize human skin and mucosal surfaces, but under conditions of impaired host immune system change into dangerous pathogens. The pathogenicity of these fungi is typically accompanied by increased adhesion and formation of complex biofilms, making candidal infections challenging to treat. Although a variety of antifungal drugs have been developed that preferably attack the fungal cell wall and plasma membrane, these pathogens have acquired novel defense mechanisms that make them resistant to standard treatment. This causes an increase in the incidence of candidiasis and enforces the urgent need for an intensified search for new specifics that could be helpful, alone or synergistically with traditional drugs, for controlling Candida pathogenicity. Currently, numerous reports have indicated the effectiveness of plant metabolites as potent antifungal agents. These substances have been shown to inhibit growth and to alter the virulence of different Candida species in both the planktonic and hyphal form and during the biofilm formation. This review focuses on the most recent findings that provide evidence of decreasing candidal pathogenicity by different substances of plant origin, with a special emphasis on the mechanisms of their action. This is a particularly important issue in the light of the currently increasing frequency of emerging Candida strains and species resistant to standard antifungal treatment.

Yeast biofilm in food realms: occurrence and control

In natural environments, microorganisms form microbial aggregates called biofilms able to adhere to a multitude of different surfaces. Yeasts make no exception to this rule, being able to form biofilms in a plethora of environmental niches. In food realms, yeast biofilms may cause major problems due to their alterative activities. In addition, yeast biofilms are tenacious structures difficult to eradicate or treat with the current arsenal of antifungal agents. Thus, much effort is being made to develop novel approaches to prevent and disrupt yeast biofilms, for example through the use of natural antimicrobials or small molecules with both inhibiting and dispersing properties. The aim of this review is to provide a synopsis of the most recent literature on yeast biofilms regarding: (i) biofilm formation mechanisms; (ii) occurrence in food and in food-related environments; and (iii) inhibition and dispersal using natural compounds, in particular.

"Inhibitory effect of Brazilian red propolis on Candida biofilms developed on titanium surfaces"

BACKGROUND

Peri-implant inflammation resulting from the presence of Candida biofilms may compromise the longevity of implant-supported dentures. This study evaluated the inhibitory effect of Brazilian red propolis on mono-species biofilms of C. albicans (ATCC 90028) and co-culture biofilms of C. albicans (ATCC 90028) and C. glabrata (ATCC 2001), developed on titanium surfaces.

METHODS

Titanium specimens were pre-conditioned with artificial saliva and submitted to biofilm formation (1 × 106 CFU/mL). After 24 h (under microaerophilic conditions at 37 °C) biofilms were submitted to treatment for 10 min, according to the groups: sterile saline solution (growth control), 0.12% chlorhexidine and 3% red propolis extract. Treatments were performed every 24 h for 3 days and analyses were conducted 96 h after initial adhesion. After that, the metabolic activity (MTT assay) (n = 12/group), cell viability (CFU counts) (n = 12/group) and surface roughness (optical profilometry) (n = 6/group) were evaluated. Data from viability and metabolic activity assays were evaluated by ANOVA and Tukey tests. Surface roughness analysis was determined by Kruskal Wallis e Mann Whitney tests.

RESULTS

Regarding the mono-species biofilm, the cell viability and the metabolic activity showed that both chlorhexidine and red propolis had inhibitory effects and reduced the metabolism of biofilms, differing statistically from the growth control (p < 0.05). With regards the co-culture biofilms, chlorhexidine had the highest inhibitory effect (p < 0.05). The metabolic activity was reduced by the exposure to chlorhexidine and to red propolis, different from the growth control group (p < 0.05). The surface roughness (Sa parameter) within the mono-species and the co-culture biofilms statistically differed among groups (p < 0.05).

CONCLUSIONS

Brazilian red propolis demonstrated potential antifungal activity against Candida biofilms, suggesting it is a feasible alternative for the treatment of peri-implantitis.

Inhibitory Effects of Berberine Hydrochloride on Trichophyton mentagrophytes and the Underlying Mechanisms

BACKGROUND

T. mentagrophytes can infect all mammals, including rabbits, causing serious infections with remarkable economic losses for rabbit farmers. Berberine is an alkaloid that is effective against a variety of microbial infections such as T. mentagrophytes. Growth curve by dry weight determination and in-vivo antifungal assay were carried out to clarify the inhibitory effect of berberine hydrochloride against T. mentagrophytes. Transcriptomics analyses were also carried out for better understanding of the underlying mechanisms.

RESULTS

The growth rate of T. mentagrophytes was significantly higher in control condition than under berberine hydrochloride or clotrimazole for 60 h. The growth rate of T. mentagrophytes was significantly slighter higher in berberine condition (1 mg) than under clotrimazole for 46 h. T. mentagrophytes seriously shrunk after berberine or clotrimazole treatment, as observed by TEM and in SEM. Significant recovery was evident in three berberine groups on day 6 compared with the DMSO group. Results from transcriptomics analyses showed 18,881 identified unigenes, including 18,754 and 12,127 in the NT and SwissProt databases. Among these, 12,011, 9174, and 11,679 unigenes belonged to 3 Gene Ontology (GO), 43 KEGG, and 25 KOG categories, respectively. Interestingly, we found that down-regulation of 14α-demethylase exposed to various medicines was slightly different, i.e., berberine hydrochloride (fold change -3.4956) and clotrimazole (fold change -2.1283) caused various degrees of alteration.

CONCLUSIONS

Berberine hydrochloride could inhibit the growth of T. mentagrophytes. Berberine hydrochloride could also cure dermatosis induced by T. mentagrophytes. Down-regulation of 14α-demethylase exposed to various medicines was slightly different and might be one of the anti-resistance mechanisms of berberine hydrochloride in T. mentagrophytes. The present investigation provides considerable transcript sequence data that would help further assess the antifungal mechanisms against T. mentagrophytes, for antifungal medicine development.

Essential oils and their components are a class of antifungals with potent vapour-phase-mediated anti-Candida activity

Multi-resistant microorganisms continue to challenge medicine and fuel the search for new antimicrobials. Here we show that essential oils and their components are a promising class of antifungals that can have specific anti-Candida activity via their vapour-phase. We quantify the vapour-phase-mediated antimicrobial activity (VMAA) of 175 essential oils and 37 essential oil components, representing more than a 1,000 unique molecules, against C. albicans and C. glabrata in a novel vapour-phase-mediated susceptibility assay. Approximately half of the tested essential oils and their components show growth-inhibitory VMAA. Moreover, an average greater activity was observed against the intrinsically more resistant C. glabrata, with essential oil component citronellal having a highly significant differential VMAA. In contrast, representatives of each class of antifungals currently used in clinical practice showed no VMAA. The vapour-phase-mediated susceptibility assay presented here thus allows for the simple detection of VMAA and can advance the search for novel (applications of existing) antimicrobials. This study represents the first comprehensive characterisation of essential oils and their components as a unique class of antifungals with antimicrobial properties that differentiate them from existing antifungal classes.