Novel mechanisms of surfactants against Candida albicans growth and morphogenesis

Surfactants' Interplay with Biofilm Development in Staphylococcus and Candida

The capacity of micro-organisms to form biofilms is a pervasive trait in the microbial realm. For pathogens, biofilm formation serves as a virulence factor facilitating successful host colonization. Simultaneously, infections stemming from biofilm-forming micro-organisms pose significant treatment challenges due to their heightened resistance to antimicrobial agents. Hence, the quest for active compounds capable of impeding microbial biofilm development stands as a pivotal pursuit in biomedical research. This study presents findings concerning the impact of three surfactants, namely, polysorbate 20 (T20), polysorbate 80 (T80), and sodium dodecyl sulfate (SDS), on the initial stage of biofilm development in both Staphylococcus aureus and Candida dubliniensis. In contrast to previous investigations, we conducted a comparative assessment of the biofilm development capacity of these two taxonomically distant groups, predicated on their shared ability to reduce TTC. The common metabolic trait shared by S. aureus and C. dubliniensis in reducing TTC to formazan facilitated a simultaneous evaluation of biofilm development under the influence of surfactants across both groups. Our results revealed that surfactants could impede the development of biofilms in both species by disrupting the initial cell attachment step. The observed effect was contingent upon the concentration and type of compound, with a higher inhibition observed in culture media supplemented with SDS. At maximum concentrations (5%), T20 and T80 significantly curtailed the formation and viability of S. aureus and C. dubliniensis biofilms. Specifically, T20 inhibited biofilm development by 75.36% in S. aureus and 71.18% in C. dubliniensis, while T80 exhibited a slightly lower inhibitory effect, with values ranging between 66.68% (C. dubliniensis) and 65.54% (S. aureus) compared to the controls. Incorporating these two non-toxic surfactants into pharmaceutical formulations could potentially enhance the inhibitory efficacy of selected antimicrobial agents, particularly in external topical applications.

Increased Absorption and Inhibitory Activity against Candida spp. of Imidazole Derivatives in Synergistic Association with a Surface Active Agent

This paper's purpose was to evaluate the interaction between three imidazole derivatives, (2-methyl-1H-imidazol-1-yl)methanol (SAM3), 1,1'-methanediylbis(1H-benzimidazole (AM5) and (1H-benzo[d]imidazol-1-yl)methanol 1-hydroxymethylbenzimidazole (SAM5) on the one hand, and sodium dodecyl sulphate (SDS) on the other, as antifungal combinations against Candida spp. Inhibitory activity was assessed using the agar diffusion method and Minimal Inhibitory Concentration (MIC) and showed moderate inhibitory activity of single imidazole derivatives against Candida spp. The mean value of MIC ranged from 200 µg/mL (SAM3) to 312.5 µg/mL (SAM3), while for SDS the MIC was around 1000 µg/mL. When used in combination with SDS, the imidazole derivatives demonstrated an improvement in their antifungal activity. Their MIC decreased over five times for AM5 and over seven times for SAM3 and SAM5, respectively, and ranged from 26.56 µg/mL (SAM3) to 53.90 µg/mL (AM5). Most combinations displayed an additive effect while a clear synergistic effect was recorded in only a few cases. Thus, the FIC Index (FICI) with values between 0.311 and 0.375 showed a synergistic effect against Candida spp. when SDS was associated with SAM3 (three strains), SAM5 (two strains) and AM5 (one strain). The association of imidazole derivatives with SDS led to the increased release of cellular material as well as the intracellular influx of crystal violet (CV), which indicated an alteration of the membrane permeability of Candida spp. cells. This favored the synergistic effect via increasing the intracellular influx of imidazoles.

Biocidal and antibiofilm activities of arginine-based surfactants against Candida isolates

Amino-acid-based surfactants are a group of compounds that resemble natural amphiphiles and thus are expected to have a low impact on the environment, owing to either the mode of surfactant production or its means of disposal. Within this context, arginine-based tensioactives have gained particular interest, since their cationic nature-in combination with their amphiphilic character-enables them to act as broad-spectrum biocides. This capability is based mainly on their interactive affinity for the microbial envelope that alters the latter's structure and ultimately its function. In the work reported here, we investigated the efficiency of Nα-benzoyl arginine decyl- and dodecylamide against Candida spp. to further our understanding of the antifungal mechanism involved. For the assays, both a Candida albicans and a Candida tropicalis clinical isolates along with a C. albicans-collection strain were used as references. As expected, both arginine-based compounds proved to be effective against the strains tested through inhibiting both the planktonic and the sessile growth. Furthermore, atomic force microscopy techniques and lipid monolayer experiments enabled us to gain insight into the effect of the surfactant on the cellular envelope. The results demonstrated that all the yeasts treated exhibited changes in their exomorphologic structure, with respect to alterations in both roughness and stiffness, relative to the nontreated ones. This finding-in addition to the amphiphiles' proven ability to insert themselves within this model fungal membrane-could explain the changes in the yeast-membrane permeability that could be linked to viability loss and mixed-vesicle release.

Improving rhamnolipids production using fermentation-foam fractionation coupling system: cell immobilization and waste frying oil emulsion

This work focused on the development of an inexpensive carbon source and the improvement of the fermentation-foam fractionation coupling system. The rhamnolipids production capacity of waste frying oil (WFO) was evaluated. The suitable bacterial cultivation of seed liquid and the addition amount of WFO was 16 h and 2% (v/v), respectively. A combined strategy of cell immobilization and oil emulsion avoid cell entrainment inside foam and improves the oil mass transfer rate. The immobilization conditions of bacterial cells into alginate-chitosan-alginate (ACA) microcapsules were optimized using the response surface method (RSM). Under the optimal conditions, rhamnolipids production using batch fermentation with immobilized strain reached 7.18 ± 0.23% g/L. WFO was emulsified into a fermentation medium using rhamnolipids as emulsifier (0.5 g/L). By monitoring dissolved oxygen, 30 mL/min was selected as a suitable air volumetric flow rate for fermentation-foam fractionation coupling operation. The total production and recovery percentage of rhamnolipids were 11.29 ± 0.36 g/L and 95.62 ± 0.38%, respectively.

Liquid crystal precursor system as a vehicle for curcumin-mediated photodynamic inactivation of oral biofilms

Curcumin has great potential as a photosensitizer, but it has low solubility in aqueous solutions. This study reports the antimicrobial efficacy of photodynamic inactivation (PDI) mediated by a curcumin-loaded liquid crystal precursor (LCP) on in situ dental biofilms. Thirty volunteers used intraoral devices containing enamel samples for 48 hours for biofilm formation. The samples were then removed from the device and treated either with LCP with 160 μM of curcumin plus illumination at 18 J/cm² (C + L+ group) or with LCP without curcumin in the dark (C - L - group). Following this, the biofilm from the samples was plated for quantifying the viable colonies at 37°C for 48 hours. Specific and nonspecific media were used for the presumptive isolation of Streptococcus mutans, Lactobacillus species/aciduric microorganisms, Candida species, and total microbiota. The C + L+ group showed a highly significant (P < .001) reduction in the log₁₀ (colony forming units/mL) values as compared to the C - L - group for all culture media. Hierarchical linear regression indicated that there may be predictors at individual volunteer level explaining the difference in the PDI efficacy among different individuals (P = .001). The LCP system retained curcumin and released it slowly and continuously, thus protecting the drug from photodegradation. LCP with curcumin is considered effective for the photoinactivation of dental biofilms, but the PDI efficacy may differ based on the host's individual characteristics.

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.

Promising Anti-Biofilm Agents and Phagocytes Enhancers for the Treatment of Candida albicans Biofilm–Associated Infections

Little is known about the interactions among phagocytes and antifungal agents and the antifungal immunomodulatory activities on Candida species biofilms. Here, inhibition of C. albicans biofilms and the interactions among biofilms and phagocytes alone or in combination with essential oils, biological, and chemical agents, or fluconazole were investigated. Biofilm formation by a panel of 28 C. albicans clinical isolates from hospitalized patients, birds, and cattle was tested. The anti-biofilm activities of cinnamon and clove oils, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and Enterococcus faecalis cell-free supernatant (CFS) in comparison with fluconazole were investigated using crystal violet and XTT reduction assays, expression of hypha-specific and hyphal regulator genes, and scanning electron microscopy (SEM) analysis. Of the tested C. albicans isolates, 15 of 28 (53.6%) were biofilm producers. Cinnamon followed by E. faecalis–CFS, SDS, and CTAB was the most effective inhibitors of planktonic C. albicans and biofilms. Fluconazole was an ineffective inhibitor of C. albicans biofilms. Sessile minimal inhibitory concentration (SMIC₅₀) of cinnamon, SDS, CTAB, and E. faecalis–CFS downregulated the hypha-specific and regulator genes, albeit to various extents, when compared with untreated biofilms (P < 0.001). SEM analysis revealed disruption and deformity of three-dimensional structures in cinnamon oil–treated biofilms. C. albicans sessile cells within biofilm were less susceptible to phagocytosis than planktonic cells. The additive effects of phagocytes and the tested antifungals enabled phagocytes to engulf C. albicans cells rapidly in cinnamon, E. faecalis–CFS, or SDS-treated biofilms. No differences in anti-Candida or anti-biofilm eradication activities were detected among the tested isolates. Our findings reinforce the substantial anti-biofilm activity of cinnamon oil, SDS, and E. faecalis–CFS and provide new avenues for the development of novel anti-biofilm immunotherapies or antifungals that could be used prior to or during the management of cases with biofilm-associated infections.

Enzymatic Production of Lauroyl and Stearoyl Monoesters of d-Xylose, l-Arabinose, and d-Glucose as Potential Lignocellulosic-Derived Products, and Their Evaluation as Antimicrobial Agents

Forestry and agricultural industries constitute highly relevant economic activities globally. They generate large amounts of residues rich in lignocellulose that have the potential to be valorized and used in different industrial processes. Producing renewable fuels and high-value-added compounds from lignocellulosic biomass is a key aspect of sustainable strategies and is central to the biorefinery concept. In this study, the use of biomass-derived monosaccharides for the enzymatic synthesis of sugar fatty acid esters (SFAEs) with antimicrobial activity was investigated to valorize these agro-industrial residues. With the aim to evaluate if lignocellulosic monosaccharides could be substrates for the synthesis of SFAEs, d-xylose, l-arabinose, and d-glucose, lauroyl and stearoyl monoesters were synthetized by transesterification reactions catalyzed by Lipozyme RM IM as biocatalyst. The reactions were performed using commercial d-xylose, l-arabinose, and d-glucose separately as substrates, and a 74:13:13 mixture of these sugars. The proportion of monosaccharides in the latter mixture corresponds to the composition found in hemicellulose from sugarcane bagasse and switchgrass, as previously described in the literature. Products were characterized using nuclear magnetic resonance (NMR) spectroscopy and showed that only the primary hydroxyl group of these monosaccharides is involved in the esterification reaction. Antimicrobial activity assay using several microorganisms showed that 5-O-lauroyl-d-xylofuranose and 5-O-lauroyl-l-arabinofuranose have the ability to inhibit the growth of Gram-positive bacteria separately and in the products mix. Furthermore, 5-O-lauroyl-l-arabinofuranose was the only product that exhibited activity against Candida albicans yeast, and the four tested filamentous fungi. These results suggest that sugar fatty acid esters obtained from sustainable and renewable resources and produced by green methods are promising antimicrobial agents.

Microcystins can be extracted from Microcystis aeruginosa using amino acid-derived biosurfactants

Microcystin, a cyanotoxin produced by Microcystis aeruginosa growing in eutrophic waters, can promote liver tumors in people ingesting contaminated water. To date, water treatment systems have not been effective in removing or degrading these cyanotoxins. In this work, we investigated the inhibitory activity of surfactants on the growth of M. aeruginosa and their application to extract the intracellular produced cyanotoxins. The experiments involving growth inhibition and extraction of cyanotoxins were carried out using the non-biodegradable surfactant cetyl trimethyl ammonium bromide (CTAB) in addition to other biodegradable surfactants. These were Tween 80 and surfactants derived from amino acids and peptides, respectively, from arginine, SDA, and hydrolyzed peptone, SDP. We demonstrated that the tested surfactants could be used to inhibit the growth of M. aeruginosa. At this point, CTAB and SDA proved to be the most competent surfactants in reducing cyanobacterial growth. Moreover, microcystins have been successfully removed from the water employing a cloud point extraction protocol based on the use of these surfactants and ammonium sulfate.

Arginine-phenylalanine and arginine-tryptophan-based surfactants as new biocompatible antifungal agents and their synergistic effect with Amphotericin B against fluconazole-resistant Candida strains

In the past two decades, the increase in microbial resistance to conventional antimicrobials has spurred scientists around the world to search tirelessly for new treatments. Synthetic amino acid-based surfactants constitute a promising alternative to conventional antimicrobial compounds. In this work, two new cationic amino acid-based surfactants were synthesized and their physicochemical, antifungal and antibiofilm properties evaluated. The surfactants were based on phenylalanine-arginine (LPAM) and tryptophan-arginine (LTAM) and prepared from renewable raw materials using a simple chemical procedure. The critical micelle concentrations of the new surfactants were determined by conductivity and fluorescence. Micellization of LPAM and LTAM took place at 1.05 and 0.54 mM, respectively. Both exhibited good antifungal activity against fluconazole-resistant Candida spp. strains, with a low minimum inhibitory concentration (8.2 μg/mL). Their mechanism of action involves alterations in cell membrane permeability and mitochondrial damage, leading to death by apoptosis. Furthermore, when LPAM and LTAM were applied with Amphotericin B, a significant synergistic effect was observed against all the studied Candida strains. These new cationic surfactants are also able to disperse biofilms of Candida spp. at low concentrations. The results indicate that LPAM and LTAM have potential application to combat the advance of fungal resistance as well as microbial biofilms.

Biofilm eradication and antifungal mechanism of action against Candida albicans of cationic dicephalic surfactants with a labile linker

Our research aims to expand the knowledge on relationships between the structure of cationic dicephalic surfactants—N,N-bis[3,3_-(dimethylamine)propyl]alkylamide dihydrochlorides and N,N-bis[3,3_-(trimethylammonio)propyl]alkylamide dibromides (alkyl: n-C9H19, n-C11H23, n-C13H27, n-C15H31)—and their antifungal mechanism of action on Candida albicans. The mentioned groups of amphiphilic substances are characterized by the presence of a weak, hydrochloride cationic center readily undergoing deprotonation, as well as a stable, strong quaternary ammonium group and alkyl chains capable of strong interactions with fungal cells. Strong fungicidal properties and the role in creation and eradication of biofilm of those compounds were discussed in our earlier works, yet their mechanism of action remained unclear. It was shown that investigated surfactants induce strong oxidative stress and cause increase in cell membrane permeability without compromising its continuity, as indicated by increased potassium ion (K⁺) leakage. Thus experiments carried out on the investigated opportunistic pathogen indicate that the mechanism of action of the researched surfactants is different than in the case of the majority of known surfactants. Results presented in this paper significantly broaden the understanding on multifunctional cationic surfactants and their mechanism of action, as well as suggest their possible future applications as surface coating antiadhesives, fungicides and antibiofilm agents in medicine or industry.

Sweet surfactants I: Fatty acid esters of sucralose

Surface active agents derived from the non-toxic sweetener sucralose and fatty acids of different chain length were synthesized. Obtained compounds were characterized chemically and with regard to their properties as emulsifying agents, antimicrobial preservatives and fat-soluble sweeteners. Results show that sucralose-fatty acid esters are possible multi-purpose additives, compatible with both cosmetic and edible emulsions, as well as purely oil-based, waterless formulations. Their relative effectiveness in those applications varies, and is highly dependent on the fatty acid chain length, with hydrophobic/hydrophilic character strongly impacting both emulsifying and antimicrobial properties. While the structural differences between sucrose and sucralose proved to be enough to push all of the newly synthesized compounds out of the detergent/solubilizer category of surfactants, the retention of the substrate's high sweetness is an indication that non-bitter compounds with washing capabilities are possible to obtain.

Effect of Carum carvi essential oil on ERG6 gene expression and virulence factors in Candida albicans

Background and Purpose:

The present study was conducted to investigate the inhibitory effects of Carum carvi essential oil (EO) against ERG6 gene expression in relation to fungal growth and some important virulence factors in Candida albicans.

Materials and Methods:

The minimum inhibitory concentration (MIC) of C. carvi EO against C. albicans was determined by the Clinical and Laboratory Standards Institute M27-A4 method at a concentration range of 20-1280 μg/ml. Furthermore, the expression of ERG6 gene was studied at the 0.5× MIC concentration of C. carvi EO using real-time polymerase chain reaction. The proteinase and phospholipase activities, cell surface hydrophobicity (CSH), and cell membrane ergosterol (CME) content of C. albicans were also assessed at the 0.5× MIC concentration of the plant EO using the approved methods. In addition, fluconazole (FLC) was used as a control antifungal drug.

Results:

The results indicated that the MIC and minimum fungicidal concentration of C. carvi EO for C. albicans growth were 320 and 640 μg/ml, respectively. The expression of fungal ERG6 at an mRNA level and ergosterol content of yeast cells were significantly decreased by both C. carvi EO (640 μg/ml) and FLC (2 μg/ml). The proteinase and phospholipase activities were also reduced in C. carvi EO by 49.82% and 53.26%, respectively, while they were inhibited in FLC-treated cultures by 27.72% and 34.67%, respectively. Furthermore, the CSH was inhibited in EO- and FLC-treated cultures by 12.75% and 20.80%, respectively.

Conclusion:

Our findings revealed that C. carvi EO can be considered a potential natural compound in the development of an efficient antifungal agent against C. albicans.

Multifunctional cationic surfactants with a labile amide linker as efficient antifungal agents-mechanisms of action

Our research aimed to expand the knowledge of relationships between the structure of multifunctional cationic dicephalic surfactants with a labile linker-N,N-bis[3,3-(dimethylamine)propyl]alkylamide dihydrochlorides and N,N-bis[3,3-(trimethylammonio)propyl]alkylamide dibromides (alkyl: n-C₉H₁₉, n-C₁₁H₂₃, n-C₁₃H₂₇, n-C₁₅H₃₁)-and their possible mechanism of action on fungal cells using the model organism Saccharomyces cerevisiae. General studies performed on surfactants suggest that in most cases, their main mechanism of action is based on perforation of the cell membranes and cell disruption. Experiments carried out in this work with cationic dicephalic surfactants seem to modify our understanding of this issue. It was found that the investigated compounds did not cause perforation of the cell membrane and could only interact with it, increasing its permeability. The surfactants tested can probably penetrate inside the cells, causing numerous morphological changes, and contribute to disorders in the lipid metabolism of the cell resulting in the formation of lipid droplet aggregates. This research also showed that the compounds cause severe oxidative stress within the cells studied, including increased production of superoxide anion radicals and mitochondrial oxidative stress. Dicephalic cationic surfactants due to their biodegradability do not accumulate in the environment and in the future may be used as effective antifungal compounds in industry as well as medicine, which will be environmentally friendly. KEY POINTS: • Dicephalic cationic surfactants do not induce disruption of the cell membrane. • Surfactants could infiltrate into the cells and cause accumulation of lipids. • Surfactants could cause acute oxidative stress in yeast cells. • Compounds present multimodal mechanism of action. Graphical abstract.

Antifungal and antiprotozoal green amino acid-based rhamnolipids: Mode of action, antibiofilm efficiency and selective activity against resistant Candida spp. strains and Acanthamoeba castellanii

Nowadays, infections caused by fungi and protists constitute a serious problem for public health services. The limited number of treatment options coupled with the increasing number of resistant microorganisms makes necessary the development of new non-toxic antifungal and antiprotozoal agents. Cationic amino acid-based rhamnolipids have been recently prepared by our group and exhibited good antibacterial activity. In this work, the antifungal, antibiofilm and antiprotozoal activity of these new rhamnolipids was investigated against a collection of fluconazole-resistant strains of different Candida species and Acanthamoeba castellanii, respectively. The arginine-RLs exhibited good antifungal activity against all fluconazole-resistant Candida spp. strains tested at MICs ranging from 6.5 to 20.7 mg/L. Their mechanism of action involves alterations in the permeability of the cell membranes that provoke death by apoptosis. The Arginine based-RLs also disperse Candida biofilms at low concentrations, similar to the MICs. All RLs tested (anionic and cationic) showed antiprotozoal activity, the arginine derivatives had the best activity killing the Acanthamoeba castellanii at concentrations of 4 mg/L. Interestingly, these surfactants have a wide range of action against yeast and A. castellanii in which they do not show toxicity against keratinocytes and fibroblasts. These results indicate that these new rhamnolipids have a sufficiently wide safety margin to be considered good candidates for several pharmaceutical applications such as combating fungal resistance and microbial biofilms and the formulation of antiprotozoal drugs.

Mucoadhesive Electrospun Fibre-Based Technologies for Oral Medicine

Oral disease greatly affects quality of life, as the mouth is required for a wide range of activities including speech, food and liquid consumption. Treatment of oral disease is greatly limited by the dose forms that are currently available, which suffer from short contact times, poor site specificity, and sensitivity to mechanical stimulation. Mucoadhesive devices prepared using electrospinning offer the potential to address these challenges by allowing unidirectional site-specific drug delivery through intimate contact with the mucosa and with high surface areas to facilitate drug release. This review will discuss the range of electrospun mucoadhesive devices that have recently been reported to address oral inflammatory diseases, pain relief, and infections, as well as new treatments that are likely to be enabled by this technology in the future.

The antifungal activities and biological consequences of BMVC-12C-P, a carbazole derivative against Candida species

Fungal infections, particularly Candida species, have increased worldwide and caused high morbidity and mortality rates. The toxicity and development of resistance in present antifungal drugs justify the need of new drugs with different mechanism of action. BMVC-12C-P, a carbazole-type compound, has been found to dysfunction mitochondria. BMVC-12C-P displayed the strongest antifungal activities among all of the BMVC derivatives. The minimal inhibitory concentration (MIC) of BMVC-12C-P against Candida species ranged from 1 to 2 μg/ml. Fluconazole-resistant clinical isolates of Candida species were highly susceptible to BMVC-12C-P. The potent fungicidal activity of BMVC-12C-P relates to its impairing mitochondrial function. Furthermore, we found that the hyphae growth and biofilm formation were suppressed in C. albicans survived from BMVC-12C-P treatment. This study demonstrates the potential of BMVC-12C-P as an antifungal agent for treating Candida infections.

Medium-Chain Fatty Acids Released from Polymeric Electrospun Patches Inhibit Candida albicans Growth and Reduce the Biofilm Viability

Oral candidiasis is a very common oral condition among susceptible individuals, with the main causative organism being the fungus Candida albicans. Current drug delivery systems to the oral mucosa are often ineffective because of short drug/tissue contact times as well as increased prevalence of drug-resistant Candida strains. We evaluated the potency of saturated fatty acids as antifungal agents and investigated their delivery by novel electrospun mucoadhesive oral patches using agar disk diffusion and biofilm assays. Octanoic (C8) and nonanoic (C9) acids were the most effective at inhibiting C. albicans growth on disk diffusion assays, both in solution or when released from polycaprolactone (PCL) or polyvinylpyrrolidone/RS100 (PVP/RS100) electrospun patches. In contrast, dodecanoic acid (C12) displayed the most potent antifungal activity against pre-existing C. albicans biofilms in solution or when released by PCL or PVP/RS100 patches. Both free and patch-released saturated fatty acids displayed a significant toxicity to wild-type and azole-resistant strains of C. albicans. These data not only provide evidence that certain saturated fatty acids have the potential to be used as antifungal agents but also demonstrate that this therapy could be delivered directly to Candida-infected sites using electrospun mucoadhesive patches, demonstrating a potential new therapeutic approach to treat oral thrush.

Antifungal Activity of Morpholine and Piperidine Based Surfactants

Microorganisms have the remarkable capacity to develop resistance to antimicrobial agents. This is of particular concern for fungal pathogens which cause devastating invasive infections with limited treatment options. Thus the need for new antifungal agents is undeniable. This work presents the antifungal properties of four surfactant groups, namely two groups of sulfobetaines and two groups of quaternary ammonium compounds, all morpholine and piperidine derivatives, against drug susceptible or drug resistant Candida albicans and Cryptococcus neoformans. The values of minimum inhibitory and fungicidal concentrations were determined. As follows from the results, the activities of the obtained compounds differed, however the most active agents from each homologous series of compounds, such as P16S3, P16S4 and C16S3, were pointed out.

Extraction and isolation of the active ingredients of dandelion and its antifungal activity against Candida albicans

In this study, six compounds were isolated and purified from dandelion, and only sample I exhibited notable antifungal effect on Candida albicans (CA). high-performance liquid chromatography-diode-array detector-electrospray ionization-tandem mass spectrometry analysis showed that sample I comprised 4-coumaric acid, ferulic acid, quercetin pentoside, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, luteolin, and two unknown compounds, at a relative percent composition of 11.45, 3.96, 10.48, 34.24, 3.91, 11.80, 3.65 and 4.21%, respectively. Further antimicrobial experiments showed that the minimum inhibitory concentration of sample I was 32.0 mg/ml, and sample I mainly acts on bacterial growth in the exponential phase of CA growth. Optical density and infrared analyses conclusively suggested that sample I damages the structure of CA cells, particularly the cell wall and cell membrane, resulting in macromolecule leakage of intracellular nucleic acids and cell metabolism disruption. In conclusion, dandelion sample I was reported to increase CA cell membrane permeability by affecting the glycosidic bond in β-(1–3)-D glucan and destroying the cell wall, ultimately leading CA to death.

Disruption of Membrane Integrity by the Bacterium-Derived Antifungal Jagaricin

Jagaricin is a lipopeptide produced by the bacterial mushroom pathogen Janthinobacterium agaricidamnosum, the causative agent of mushroom soft rot disease. Apart from causing lesions in mushrooms, jagaricin is a potent antifungal active against human-pathogenic fungi. We show that jagaricin acts by impairing membrane integrity, resulting in a rapid flux of ions, including Ca2+, into susceptible target cells. Accordingly, the calcineurin pathway is required for jagaricin tolerance in the fungal pathogen Candida albicans Transcriptional profiling of pathogenic yeasts further revealed that jagaricin triggers cell wall strengthening, general shutdown of membrane potential-driven transport, and the upregulation of lipid transporters, linking cell envelope integrity to jagaricin action and resistance. Whereas jagaricin shows hemolytic effects, it exhibited either no or low plant toxicity at concentrations at which the growth of prevalent phytopathogenic fungi is inhibited. Therefore, jagaricin may have potential for agricultural applications. The action of jagaricin as a membrane-disrupting antifungal is promising but would require modifications for use in humans.

Antifungal Activity of Arginine-Based Surfactants

Background:

Amino acid based surfactants constitute an important class of surface active biomolecules showing remarkable biocompatible properties. Antimicrobial activity is one of the most remarkable biological properties of this kind of surfactants, which have been widely studied against a broad spectrum of microorganisms. However, the antifungal activity of this kind of compound has been less well investigated. The aim of this work is the study of the antifungal activity of two novel argininebased surfactants (Nα-benzoyl-arginine decylamide, Bz-Arg-NHC10 and Nα-benzoyl-arginine dodecylamide, Bz-Arg-NHC12), obtained by an enzymatic strategy, against phytopathogenic filamentous fungi and dermatophyte strains.

Methods:

Four phytopathogenic fungi (Fusarium oxysporum, Fusarium solani, Colletotrichum gloeosporioides and Colletotrichum lindemuthianum) and two human pathogenic fungi (dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes) were tested. Inhibition of vegetative growth and conidia germination was investigated for the phytopathogenic fungi. In order to elucidate the possible mechanism of biocide action, membrane integrity, as well as the production of reactive oxygen species (ROS) were evaluated. Additionally, the inhibition of germination of dermatophyte microconidia due to both arginine-based surfactants was studied. Minimum inhibitory concentration, as well as the concentration that inhibits 50% of germination were determined for both compounds and both fungal strains.

Results:

For the vegetative growth of phytopathogenic fungi, the most potent arginine-based compound was Bz-Arg-NHC10. All the tested compounds interfered with the conidia development of the studied species. Investigation of the possible mechanism of toxicity towards phytopathogenic fungi indicated direct damage of the plasma membrane and production of ROS. For the two strains of dermatophyte fungi tested, all the proved compounds showed similar fungistatic efficacy.

Conclusion:

: Bz-Arg-NHC10 and Bz-Arg-NHC12 were demonstrated to have broad biocidal ability against the proliferative vegetative form and the asexual reproductive conidia. Results suggest that both membrane permeabilization and induction of oxidative stress are part of the antifungal mechanisms involved in the interruption of normal conidia development by Bz-Arg-NHCn, leading to cell death.

Surfactants: Role in biofilm management and cellular behaviour

Appropriate and effective wound cleaning represents an important process that is necessary for preparing the wound for improved wound healing and for helping to dislodge biofilms. Wound cleaning is of paramount importance to wound bed preparation for helping to enhance wound healing. Surfactant applications in wound care may represent an important area in the cleaning continuum. However, understanding of the role and significance of surfactants in wound cleansing, biofilm prevention and control, and enhancing cellular viability and proliferation is currently lacking. Despite this, some recent evidence on poloxamer-based surfactants where the surfactants are present in high concentration have been shown to have an important role to play in biofilm management; matrix metalloproteinase modulation; reducing inflammation; and enhancing cellular proliferation, behaviour, and viability. Consequently, this review aims to discuss the role, mode of action, and clinical significance of the use of medically accepted surfactants, with a focus on concentrated poloxamer-based surfactants, to wound healing but, more specifically, the role they may play in biofilm management and effects on cellular repair.

Colloidal Stability of Positively Charged Dispersions of Styrene and Acrylic Copolymers in the Presence of TiO2 and CaCO3

Increasing antibiotic resistance of several pathogenic microorganisms calls for alternative approaches to prevent spreading of bacterial diseases. We propose to employ for this purpose coatings obtained from positively charged latex dispersions. In this contribution we characterize aqueous mixed dispersions containing TiO2 or CaCO3 and methyl methacrylate-ethyl acrylate or styrene-ethyl acrylate copolymers synthesized using a cationic surfactant, cetyltrimethylammonium bromide as an emulsifier. Particle size, electrokinetic (ζ) potential of the mixed dispersions and the resulting thin films, as well as antimicrobial properties of the latter are described. The TiO2 and CaCO3 dispersions were stabilised with polyethyleneimine (PEI) and optimum pH for the mixed dispersions were chosen on the basis of ζ-potential measurements. For TiO2, the maximum ζ = +35 mV was found at pH 7.5, and for CaCO3, pH was set at 8.2 (ζ = +38 mV), to prevent its dissolution. In most 1:1 mixtures of TiO2 or CaCO3 with the cetyltrimethylammonium bromide (CTAB)-stabilised latex dispersions, two distinct particles populations were observed, corresponding to the bare latex and bare TiO2 or CaCO3 fractions. Films made of the mixed dispersions remained positively charged and showed antimicrobial activity similar or reduced with respect to the bare polymer films.

Antimicrobial dispersions and films from positively charged styrene and acrylic copolymers

Antimicrobial properties of methyl methacrylate - ethyl acrylate and styrene - ethyl acrylate copolymers, both as latexes and after film formation were tested. The polymers were synthesized using a cationic surfactant, cetytrimethylammonium bromide (CTAB) as an emulsifier, in presence of either a cationic or an anionic initiator. The resulting latex particles showed sizes between 50 and 320 nm (larger for the anionic initiator), and ζ-potential between +30 and +70 mV (more positive for the cationic initiator). Dialysis did not change significantly the size distribution and ζ-potential of the latexes, and most of them inhibited growth of Gram-negative (E. coli), Gram-positive (S. aureus, B. subtilis) and yeast (C. albicans). On the other hand, only few compositions were effective against Gram-negative P. aeruginosa. Both completely ("dry") and incompletely ("wet") formed films produced from the respective latexes showed similar, although less pronounced antimicrobial activity pattern. The analysis of streaming potential for the films confirmed that part of the positive surface charge brought by non-covalent binding of CTAB to the polymer chains, is lost during dialysis of the latexes and during rinsing, especially under high-shear flow. From the practical point of view, films with the best mechanical and antimicrobial properties can be achieved using polymers with high proportion of ethyl acrylate, while nature of the co-monomer and initiator do not play crucial roles.

Antifungal effects of BiOBr nanosheets carrying surfactant cetyltrimethylammonium bromide

BiOBr nanosheets are important photocatalytic nanomaterials. However, their biological effects remain to be explored. In this study, we investigated the antifungal effect of BiOBr nanosheets on Candida albicans. Strikingly, the nanosheets strongly inhibited the growth of C. albicans [IC₅₀=(96±4.7) mg/L], hyphal development and biofilm formation. Compareed to the antifungal effect of the cationic surfactant cetyltrimethylammonium bromide, the inhibitory effect of the nanosheets on fungal pathogen was attributed to cetyltrimethylammonium bromide adsorbed by the nanosheets. Thermal gravity analysis and cetyltrimethylammonium bromide release experiment indicated that only 0.42% cetyltrimethylammonium bromide on BiOBr nanosheets was released. Taken together, this study uncovers the contribution of surfactant released from the nanosheets to their antifungal activity.

The Candida albicans stress response gene Stomatin-Like Protein 3 is implicated in ROS-induced apoptotic-like death of yeast phase cells

The ubiquitous presence of SPFH (Stomatin, Prohibitin, Flotillin, HflK/HflC) proteins in all domains of life suggests that their function would be conserved. However, SPFH functions are diverse with organism-specific attributes. SPFH proteins play critical roles in physiological processes such as mechanosensation and respiration. Here, we characterize the stomatin ORF19.7296/SLP3 in the opportunistic human pathogen Candida albicans. Consistent with the localization of stomatin proteins, a Slp3p-Yfp fusion protein formed visible puncta along the plasma membrane. We also visualized Slp3p within the vacuolar lumen. Slp3p primary sequence analyses identified four putative S-palmitoylation sites, which may facilitate membrane localization and are conserved features of stomatins. Plasma membrane insertion sequences are present in mammalian and nematode SPFH proteins, but are absent in Slp3p. Strikingly, Slp3p was present in yeast cells, but was absent in hyphal cells, thus categorizing it as a yeast-phase specific protein. Slp3p membrane fluorescence significantly increased in response to cellular stress caused by plasma membrane, cell wall, oxidative, or osmotic perturbants, implicating SLP3 as a general stress-response gene. A slp3Δ/Δ homozygous null mutant had no detected phenotype when slp3Δ/Δ mutants were grown in the presence of a variety of stress agents. Also, we did not observe a defect in ion accumulation, filamentation, endocytosis, vacuolar structure and function, cell wall structure, or cytoskeletal structure. However, SLP3 over-expression triggered apoptotic-like death following prolonged exposure to oxidative stress or when cells were induced to form hyphae. Our findings reveal the cellular localization of Slp3p, and for the first time associate Slp3p function with the oxidative stress response.

An Antifungal Mechanism of Protolichesterinic Acid from the Lichen Usnea albopunctata Lies in the Accumulation of Intracellular ROS and Mitochondria-Mediated Cell Death Due to Apoptosis in Candida tropicalis

Candida species causes superficial and life-threatening systemic infections and are difficult to treat due to the resistance of these organism to various clinically used drugs. Protolichesterinic acid is a well-known lichen compound. Although the antibacterial activity of protolichesterinic acid has been reported earlier, the antifungal property and its mechanism of action are still largely unidentified. The goal of the present investigation is to explore the anticandidal activity and mechanism of action of protolichesterinic acid, especially against Candida tropicalis. The Minimum Inhibitory Concentration (MIC) value was established through microdilution techniques against four Candida species and out of four species tested, C. tropicalis showed a significant effect (MIC: 2 μg/ml). In the morphological interference assay, we observed the enhanced inhibition of hyphae when the cells were treated with protolichesterinic acid. Time-kill assay demonstrated that the maximum rate of killing was recorded between 2 and 6 h. C. tropicalis exposed to protolichesterinic acid exhibited an increased ROS production, which is one of the key factors of fungal death. The rise in ROS was due to the dysfunction of mitochondria caused by protolichesterinic acid. We confirmed that protolichesterinic acid-induced dysfunction of mitochondria in C. tropicalis. The damage of cell membrane due to protolichesterinic acid treatment was confirmed by the influx of propidium iodide and was further confirmed by the release of potassium ions. The treatment of protolichesterinic acid also triggered calcium ion signaling. Moreover, it commenced apoptosis which is clearly evidenced by Annexin V and propidium iodide staining. Interestingly protolichesterinic acid recorded excellent immunomodulatory property when tested against lymphocytes. Finally protolichesterinic acid showed low toxicity toward a normal human cell line Foreskin (FS) normal fibroblast. In in vivo test, protolichesterinic acid significantly enhanced the survival of C. tropicalis infected Caenorhabditis elegans. This investigation proposes that the protolichesterinic acid induces apoptosis in C. tropicalis via the enhanced accumulation of intracellular ROS and mitochondrial damage, which leads fungal cell death via apoptosis. Our work revealed a new key aspect of mechanisms of action of protolichesterinic acid in Candida species. This article is the first study on the antifungal and mechanism of action of protolichesterinic acid in Candida species.

Interaction of amino acid-functionalized silver nanoparticles and Candida albicans polymorphs: A deep-UV fluorescence imaging study

The interaction of the tryptophan functionalized Ag nanoparticles and live Candida albicans cells was studied by synchrotron excitation deep-ultraviolet (DUV) fluorescence imaging at the DISCO beamline of Synchrotron SOLEIL. DUV imaging showed that incubation of the fungus with functionalized nanoparticles results in significant increase in the fluorescence signal. The analysis of the images revealed that the interaction of the nanoparticles with (pseudo)hyphae polymorphs of the diploid fungus was less pronounced than in the case of yeast cells or budding spores. The changes in the intensity of the fluorescence signals of the cells after incubation were followed in [327-353nm] and [370-410nm] spectral ranges that correspond to the fluorescence of tryptophan in non-polar and polar environment, respectively. As a consequence of the environmental sensitivity of the silver-tryptophan fluorescent nanoprobe, we were able to determine the possible accumulation sites of the nanoparticles. The analysis of the intensity decay kinetics showed that the photobleaching effects were more pronounced in the case of the functionalized nanoparticle treated cells. The results of time-integrated emission in the mentioned spectral ranges suggested that the nanoparticles penetrate the cells, but that the majority of the nanoparticles attach to the cells' surfaces.

Novel strategies against Candida biofilms: interest of synthetic compounds

A biofilm is a consortium of microbial cells that are attached to a substratum or an interface. It should be considered a reservoir that may induce serious infections. Indeed, Candidaspp. biofilms may be involved in the persistence or worsening of some chronic inflammatory diseases as well as in systemic infections, which may lead to high morbidity and mortality rates. New strategies are currently being explored, utilizing several synthetic compounds to prevent or fight these Candida biofilms. This article focuses on active synthetic compounds classified with regards to their modes of action: inhibition of early adherence phase, inhibition or control of biofilm maturation and finally elimination of already formed biofilms. Some of them show promise in fighting biofilm.