1-n -Hexadecyl-3-methylimidazolium methanesulfonate and chloride salts with effective activities against Candida tropicalis biofilms

Antifouling Systems Based on a Polyhedral Oligomeric Silsesquioxane-Based Hexyl Imidazolium Salt Adsorbed on Copper Nanoparticles Supported on Titania

The reaction of octakis(3-chloropropyl)octasilsesquioxane with four equivalents of 1-hexylimidazole or 1-decylimidazole gave two products labelled as HQ-POSS (hexyl-imidazolium quaternized POSS) and DQ-POSS (decyl-imidazolium quaternized POSS) as regioisomer mixtures. An investigation of the biological activity of these two compounds revealed the higher antimicrobial performances of HQ-POSS against Gram-positive and Gram-negative microorganisms, proving its broad-spectrum activity. Due to its very viscous nature, HQ-POSS was adsorbed in variable amounts on the surface of biologically active oxides to gain advantages regarding the expendability of such formulations from an applicative perspective. Titania and 5 wt% Cu on titania were used as supports. The materials 10HQ-POSS/Ti and 15HQ-POSS/5CuTi strongly inhibited the ability of Pseudomonas PS27 cells-a bacterial strain described for its ability to handle very toxic organic solvents and perfluorinated compounds-to grow as planktonic cells. Moreover, the best formulations (i.e., 10HQ-POSS/Ti and 15HQ-POSS/5CuTi) could prevent Pseudomonas PS27 biofilm formation at a certain concentration (250 μg mL^-1) which greatly impaired bacterial planktonic growth. Specifically, 15HQ-POSS/5CuTi completely impaired cell adhesion, thus successfully prejudicing biofilm formation and proving its suitability as a potential antifouling agent. Considering that most studies deal with quaternary ammonium salts (QASs) with long alkyl chains (>10 carbon atoms), the results reported here on hexylimidazolium-based POSS further deepen the knowledge of QAS formulations which can be used as antifouling compounds.

Imidazolium Salts for Candida spp. Antibiofilm High-Density Polyethylene-Based Biomaterials

The species of Candida present good capability to form fungal biofilms on polymeric surfaces and are related to several human diseases since many of the employed medical devices are designed using polymers, especially high-density polyethylene (HDPE). Herein, HDPE films containing 0; 0.125; 0.250 or 0.500 wt% of 1-hexadecyl-3-methylimidazolium chloride (C₁₆MImCl) or its analog 1-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆MImMeS) were obtained by melt blending and posteriorly mechanically pressurized into films. This approach resulted in more flexible and less brittle films, which impeded the Candida albicans, C. parapsilosis, and C. tropicalis biofilm formation on their surfaces. The employed imidazolium salt (IS) concentrations did not present any significant cytotoxic effect, and the good cell adhesion/proliferation of human mesenchymal stem cells on the HDPE-IS films indicated good biocompatibility. These outcomes combined with the absence of microscopic lesions in pig skin after contact with HDPE-IS films demonstrated their potential as biomaterials for the development of effective medical device tools that reduce the risk of fungal infections.

Anti-barnacle biofouling coatings for the protection of marine vessels: synthesis and progress

Marine biofouling has gnawed both mobile and non-mobile marine structures since time immemorial, leading to the deterioration of designed operational capabilities as well as a loss of valuable economic revenues. Mitigation of biofouling has been the primary focus of researchers and scientists from across the globe to save billions of dollars wasted due to the biological fouling of marine structures. The availability of an appropriate environment along with favorable substrata initiates biofilm formation within a few minutes. The crucial element in establishing a gelatinous biofilm is the excreted metabolites of destructive nature and exopolymeric substances (EPSs). These help in securing as well as signaling numerous foulants to establish themselves on this substrate. The larvae of various benthic invertebrates adhere to these suitable surfaces and transform from juveniles to adult barnacles depending upon the environment. Despite biofouling being characteristically witnessed for a month or lengthier timeframe, the preliminary phases of the fouling process typically transpire on a much lesser timescale. A few natural and synthetic additives had demonstrated excellent non-toxic anti barnacle establishment capability; however, further development into commercial products is still far-fetched. This review collates the specific anti-barnacle coatings, emphasizing natural additives, their sources of extraction, general life cycle analysis, and concluding future perspectives of this niche product.

Glass ionomer cement modified by a imidazolium salt: adding antifungal properties to a biomaterial

We present the structural modification of a commercially available glass ionomer cement by inserting the imidazolium salt 1-n-hexadecyl-3-methylimidazolium chloride (C₁₆MImCl), composing a new biomaterial with antifungal biofilm activity. Test specimens were prepared using a commercial glass ionomer cement to which 10 ppm of cetylpyridinium chloride (reference ionic antifungal agent) or C₁₆MImCl were added. The feasibility and hypoallergenicity of the new biomaterial were assessed by microhardness plastic deformation and chorioallantoic membrane assays. Colony counting and scanning electron microscopy were used to evaluate the modified specimens' antibiofilm activity against three multidrug-resistant Candida species. The modified glass ionomer cement presented a strong antibiofilm activity against Candida spp., without losing its original micromechanical and hypoallergenic properties, rendering it a promising candidate for further application in dentistry.

Synergistic association of clioquinol with antifungal drugs against biofilm forms of clinical Fusarium isolates

BACKGROUND

The influence of biofilm on the complexity of fungal diseases has been reported in recent years, especially in non-invasive mycoses such as keratitis and onychomycosis. The difficulty in treating cases of fusariosis in the human medical clinic exemplifies this situation, because when Fusarium spp. are present in the form of biofilm, the permeation of antifungal agents is compromised.

OBJECTIVES

This study proposes an association of clioquinol, an inhibitor of fungal cells with antifungal drugs prescribed to combat fusariosis in humans.

METHODS

Susceptibility was assessed by microdilution in broth. Formation of biofilm by staining with violet crystal. Inhibition and removal of biofilm using the MTT colorimetric reagent. Time-kill combination, hypoallergenicity test, cytotoxicity test and toxicity prediction by computer analysis were also performed.

RESULTS

Clioquinol associated with voriconazole and ciclopirox inhibited biofilm formation. Possibly, clioquinol acts in the germination and elongation of hyphae, while voriconazole prevents cell adhesion and ciclopirox the formation of the extracellular polymeric matrix. The CLIO-VRC association reduced the biofilm formation by more than 90%, while the CLIO-CPX association prevented over 95%. None of the association was irritating, and over 90% of the leucocytes remained viable. Computational analysis does not reveal toxicity relevant to CLIO, whereas VRC and CPX showed some risks for systemic use, but suitable for topical formulations.

CONCLUSIONS

The combination of CLIO-VRC or CLIO-CPX proved to be a promising association strategy in the medical clinic, both in combating fungal keratitis and onychomycosis, since they prevent the initial process of establishing an infection, the formation of biofilm.

Alkylimidazolium Ionic Liquids as Antifungal Alternatives: Antibiofilm Activity Against Candida albicans and Underlying Mechanism of Action

Candida albicans is an opportunistic pathogen causes fungal infections that range from common skin infections to persistent infections through biofilm formation on tissues, implants and life threatening systemic infections. New antifungal agents or therapeutic methods are desired due to high incidence of infections and emergence of drug-resistant strains. The present study aimed to evaluate (i) the antifungal and antibiofilm activity of 1-alklyl-3-methyl imidazolium ionic liquids ([CnMIM]+[X]-, n = 4, 12 and 16) against Candida albicans ATCC 10231 and two clinical C. albicans strains and (ii) the mechanism of action of promising antifungal ionic liquid on C. albicans. Two of the tested compounds were identified as more effective in preventing growth and biofilm formation. These ionic liquid compounds with -dodecyl and -hexadecyl alkyl groups effectively prevented biofilm formation by fluconazole resistant C. albicans 10231 and two other clinical C. albicans strains. Although both the compounds caused viability loss in mature C. albicans biofilms, an ionic liquid with -hexadecyl group ([C16MIM]+[Cl]-) was more effective in dispersing mature biofilms. This promising ionic liquid compound ([C16MIM]+[Cl]-) was chosen for determining the underlying mode of action on C. albicans cells. Light microscopy showed that ionic liquid treatment led to a significant reduction in cell volume and length. Increased cell membrane permeability in the ionic liquid treated C. albicans cells was evident in propidium iodide staining. Leakage of intracellular material was evident in terms of increased absorbance of supernatant and release of potassium and calcium ions into extracellular medium. A decrease in ergosterol content was evident when C. albicans cells were cultured in the presence of antifungal ionic liquid. 2',7'-Dichlorodihydrofluorescein acetate assay revealed reactive oxygen species generation and accumulation in C. albicans cells upon treatment with antifungal ionic liquid. The effect of antifungal ionic liquid on mitochondria was evident by decreased membrane potential (measured by Rhodamine 123 assay) and loss of metabolic activity (measured by MTT assay). This study demonstrated that imidazolium ionic liquid compound exert antifungal and antibiofilm activity by affecting various cellular processes. Thus, imidazolium ionic liquids represent a promising antifungal treatment strategy in lieu of resistance development to common antifungal drugs.

Synthesis of new water-soluble ionic liquids and their antibacterial profile against gram-positive and gram-negative bacteria

A series of imidazolium bromide salts (NIM-Br 1a, 1b and 1c) bearing different lengths of alkyl chains were synthesized and theirin vitro antibacterial activities were determined by measuring the minimum inhibitory concentration (MIC) values for Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis. In addition, these imidazolium derivatives were also evaluated against biofilm produced by these bacterial strains. All compounds were found to be effective against Gram-positive and Gram-negative bacteria, and also more effective on the S. aureus biofilm production than the others.

Larvicidal and residual activity of imidazolium salts against Aedes aegypti (Diptera: Culicidae)

BACKGROUND

Aedes aegypti is an important mosquito species that can transmit several arboviruses such as dengue fever, yellow fever, chikungunya and zika. Because these mosquitoes are becoming resistant to most chemical insecticides used around the world, studies with new larvicides should be prioritized. Based on the known biological profile of imidazolium salts (IS), the objective of this study was to evaluate the potential of six IS as larvicides against Ae. aegypti, as tested against Ae. aegypti larvae. Larval mortality was measured after 24 and 48 h, and residual larvicidal activity was also evaluated.

RESULTS

Promising results were obtained with aqueous solutions of two IS: 1-n-octadecyl-3-methylimidazolium chloride (C₁₈ MImCl) and 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆ MImMeS), showing up to 90% larval mortality after 48 h exposure. C₁₈ MImCl was more effective than C₁₆ mIMeS, causing mortality until day 15 after exposure. An application of C₁₈ MImCl left to dry under ambient conditions for at least 2 months and then dissolved in water showed a more pronounced residual effect (36 days with 95% mortality and 80% mortality up to 78 days).

CONCLUSION

This is the first study to show the potential of IS in the control of Ae. aegypti. Further studies are needed to understand the mode of action of these compounds in the biological development of this mosquito species. © 2017 Society of Chemical Industry.

The anthraquinones rubiadin and its 1-methyl ether isolated from Heterophyllaea pustulata reduces Candida tropicalis biofilms formation

BACKGROUND

Candida tropicalis is increasingly becoming among the most commonly isolated pathogens causing fungal infections with an important biofilm-forming capacity.

PURPOSE

This study addresses the antifungal effect of rubiadin (AQ1) and rubiadin 1-methyl ether (AQ2), two photosensitizing anthraquinones (AQs) isolated from Heterophyllaea pustulata, against C. tropicalis biofilms, by studying the cellular stress and antioxidant response in two experimental conditions: darkness and irradiation. The combination with Amphotericin B (AmB) was assayed to evaluate the synergic effect.

STUDY DESIGN/METHODS

Biofilms of clinical isolates and reference strain of Candida tropicalis were treated with AQs (AQ1 or AQ2) and/or AmB, and the biofilms depletion was studied by crystal violet and confocal scanning laser microscopy (CSLM). The oxidant metabolites production and the response of antioxidant defense system were also evaluated under dark and irradiation conditions, being the light a trigger for photo-activation of the AQs. The Reactive Oxygen Species (ROS) were detected by the reduction of Nitro Blue Tetrazolium test, and Reactive Nitrogen Intermediates (RNI) by the Griess assay. ROS accumulation was also detected inside biofilms by using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) probe, which was visualized by CSLM. Superoxide dismutase (SOD) activity and the total antioxidant capacity of biofilms were measured by spectrophotometric methods. The minimun inhibitory concentration for sessile cells (SMIC) was determined for each AQs and AmB. The fractional inhibitory concentration index (FICI) was calculated for the combinations of each AQ with AmB by the checkerboard microdilution method.

RESULTS

Biofilm reduction of both strains was more effective with AQ1 than with AQ2. The antifungal effect was mediated by an oxidative and nitrosative stress under irradiation, with a significant accumulation of endogenous ROS detected by CSLM and an increase in the SOD activity. Thus, the prooxidant-antioxidant balance was altered especially by AQ1. The best synergic combination with AmB was also obtained with AQ1 (80.5%) (FICI=0.74).

CONCLUSION

Under irradiation, the oxidative stress was the predominant effect, altering the prooxidant-antioxidant balance, which may be the cause of the irreversible cell injury in the biofilm. Our results showed synergism of these natural AQs with AmB. Therefore, the photosensitizing AQ1 could be an alternative for the Candida infections treatment, which deserves further investigation.

Assessing an imidazolium salt's performance as antifungal agent on a mouthwash formulation

AIMS

This study demonstrates the development of a mouthwash formulation containing the imidazolium salt (IMS) 1-n-hexadecyl-3-methylimidazolium chloride (C₁₆ MImCl), considering its stability and efficacy against Candida sp. Biofilm formation.

METHODS AND RESULTS

A variety of in vitro test methods were applied, assessing contaminated acrylic resin strip specimens before and after applying the mouthwash formulations. The formulation using C₁₆ MImCl presented a similar antibiofilm activity to cetylpyridinium chloride one and a commercial mouthwash, but at a 10 times lower concentration. Scanning electron microscopy imaging demonstrated that the selected mouthwash preparation fully destroys the biofilm cells, while with the hypoallergenicity test no irritant effect was observed in ex vivo model.

CONCLUSIONS

The results presented herein indicate a high potential for imidazolium salts application as mouthwash agents that can eliminate Candida biofilm growth at very low concentrations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates a new and effective antibiofilm formulation containing the IMS C₁₆ MImCl. These findings suggest the IMS' use as mouthwash formulations active ingredient against Candida biofilms on oral surfaces, as it outperforms the often used cetylpyridinium chloride at a 10 times lower concentration.

Multitask Imidazolium Salt Additives for Innovative Poly(l-lactide) Biomaterials: Morphology Control, Candida spp. Biofilm Inhibition, Human Mesenchymal Stem Cell Biocompatibility, and Skin Tolerance

Candida species have great ability to colonize and form biofilms on medical devices, causing infections in human hosts. In this study, poly(l-lactide) films with different imidazolium salt (1-n-hexadecyl-3-methylimidazolium chloride (C16MImCl) and 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C16MImMeS)) contents were prepared, using the solvent casting process. Poly(l-lactide)-imidazolium salt films were obtained with different surface morphologies (spherical and directional), and the presence of the imidazolium salt in the surface was confirmed. These films with different concentrations of the imidazolium salts C16MImCl and C16MImMeS presented antibiofilm activity against isolates of Candida tropicalis, Candida parapsilosis, and Candida albicans. The minor antibiofilm concentration assay enabled one to determine that an increasing imidazolium salt content promoted, in general, an increase in the inhibition percentage of biofilm formation. Scanning electron microscopy micrographs confirmed the effective prevention of biofilm formation on the imidazolium salt containing biomaterials. Lower concentrations of the imidazolium salts showed no cytotoxicity, and the poly(l-lactide)-imidazolium salt films presented good cell adhesion and proliferation percentages with human mesenchymal stem cells. Furthermore, no acute microscopic lesions were identified in the histopathological evaluation after contact between the films and pig ear skin. In combination with the good morphological, physicochemical, and mechanical properties, these poly(l-lactide)-based materials with imidazolium salt additives can be considered as promising biomaterials for use in the manufacturing of medical devices.