Optimum Inhibition of Amphotericin-B-Resistant Candida albicans Strain in Single- and Mixed-Species Biofilms by Candida and Non-Candida Terpenoids

Chemical Composition and Antifungal Effect of the Essential Oils of Thymus vulgaris L., Origanum vulgare L., and Satureja montana L. Against Clinical Isolates of Candida spp

Infections caused by Candida species are on the rise, and the escalating concern revolves around the growing resistance to known antifungals, particularly in immunocompromised individuals. The essential oils (EOs) of thyme, oregano, and savory were studied for antifungal, antibiofilm, and potential synergistic activity against isolates of Candida. The oils underwent chemical characterization, revealing comparable compositions of the monoterpene phenols, predominantly thymol and carvacrol, albeit in varying proportions. Anti-Candida activity assessments of these EOs and the type of interactions among these agents on planktonic cells of candidal isolates were done by microdilution and the checkerboard method, respectively. Our findings underscore the significant inhibitory effects of the tested agents against both planktonic and biofilm forms of Candida cells. The minimum inhibitory concentration (MIC) values of the tested oils against planktonic Candida cells ranged from 0.312 to 2.500 mg/mL, classifying them as highly to moderately active against the causative agents of candidosis. The effect on the formation of Candida biofilms was statistically significant for the majority of the tested candidal isolates, with a reduction percentage greater than 50%. Notably, the high significance of our study lies in the presented synergistic effects observed in the majority of the examined combinations, without any presence of antagonistic interactions.

Harnessing Monoterpenes and Monoterpenoids as Weapons against Antimicrobial Resistance

Antimicrobial resistance (AMR) poses a formidable challenge in global healthcare, driving the exploration of natural products for novel antimicrobials. Among these, essential oils (EOs) derived from medicinal plants are rich sources of diverse bioactive compounds. Monoterpenes and monoterpenoids, critical constituents of EOs, have emerged as promising agents in combating multidrugresistant (MDR) pathogens. This review analyzed recent literature on the efficacy of monoterpenes against AMR, highlighting their broad-spectrum activity and potential as alternative therapeutic options for MDR infections. Mechanistic insights reveal their ability to disrupt cell membranes, inhibit biofilm formation, and modulate gene expression linked to virulence and resistance, thereby reducing microbial viability through alterations in membrane potential, enzymatic activity, and genetic regulation. Synergistic interactions between monoterpenes and conventional antibiotics are also elucidated. Innovative approaches in monoterpene research are explored, although challenges such as resistance, limited solubility, volatility, and potential toxicity are acknowledged, emphasizing the need for advanced formulation strategies and interdisciplinary research. The synergy observed with conventional antibiotics, coupled with their ability to target specific microbial resistance mechanisms, underscores the potential of monoterpenes in combating antibioticresistant infections. Future investigations should prioritize optimizing monoterpenes' therapeutic properties and assessing their safety profiles to fully exploit their potential in addressing AMR.

Carvacrol Effectively Inhibits Pseudomonas tolaasii In Vitro and Induces Resistance to Brown Blotch Disease in Postharvest Agaricus bisporus

Carvacrol (CAR), a naturally occurring phenolic monoterpene compound, has recently received attention for its potential use in food preservation. However, whether it is effective in controlling brown blotch disease caused by Pseudomonas tolaasii in edible mushrooms is unknown. The results of this study showed that CAR effectively inhibits and kills P. tolaasii in vitro by disrupting cell membrane integrity and causing the leakage of cellular components. Intracellular proteins and the DNA of P. tolaasii may not be the targets of CAR. CAR fumigation at a concentration as low as 20 μmol L-1 CAR effectively inhibited P. tolaasii-caused brown blotch disease in Agaricus bisporus, accompanied by a decrease in polyphenol oxidase activation, melanin production, and malondialdehyde accumulation. CAR treatment also significantly increased the activities of β-1,4-N-acetyl-glucosaminnidase, three antioxidant enzymes, and phenylpropanoid pathway-related enzymes, as well as promoting the accumulation of phenolic, flavonoid, and lignin substances in mushrooms, thereby inducing the resistance of mushrooms to the disease. These results demonstrate the potential application of carvacrol to control bacterial disease in A. bisporus mushrooms.

"Stop, Little Pot" as the Motto of Suppressive Management of Various Microbial Consortia

The unresolved challenges in the development of highly efficient, stable and controlled synthetic microbial consortia, as well as the use of natural consortia, are very attractive for science and technology. However, the consortia management should be done with the knowledge of how not only to accelerate but also stop the action of such "little pots". Moreover, there are a lot of microbial consortia, the activity of which should be suppressively controlled. The processes, catalyzed by various microorganisms being in complex consortia which should be slowed down or completely cancelled, are typical for the environment (biocorrosion, landfill gas accumulation, biodegradation of building materials, water sources deterioration etc.), industry (food and biotechnological production), medical practice (vaginitis, cystitis, intestinal dysbiosis, etc.). The search for ways to suppress the functioning of heterogeneous consortia in each of these areas is relevant. The purpose of this review is to summarize the general trends in these studies regarding the targets and new means of influence used. The analysis of the features of the applied approaches to solving the main problem confirms the possibility of obtaining a combined effect, as well as selective influence on individual components of the consortia. Of particular interest is the role of viruses in suppressing the functioning of microbial consortia of different compositions.

Antimicrobial and anti-biofilm properties of oleuropein against Escherichia coli and fluconazole-resistant isolates of Candida albicans and Candida glabrata

BACKGROUND

Side effects associated with antimicrobial drugs, as well as their high cost, have prompted a search for low-cost herbal medicinal substances with fewer side effects. These substances can be used as supplements to medicine or to strengthen their effects. The current study investigated the effect of oleuropein on the inhibition of fungal and bacterial biofilm in-vitro and at the molecular level.

MATERIALS AND METHODS

In this experimental study, antimicrobial properties were evaluated using microbroth dilution method. The effect of oleuropein on the formation and eradication of biofilm was assessed on 96-well flat bottom microtiter plates and their effects were observed through scanning electron microscopy (SEM). Its effect on key genes (Hwp1, Als3, Epa1, Epa6, LuxS, Pfs) involved in biofilm formation was investigated using the quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) method.

RESULTS

The minimum inhibitory concentration (MIC) and minimum fungicidal/bactericidal concentration (MFC/MBC) for oleuropein were found to be 65 mg/ml and 130 mg/ml, respectively. Oleuropein significantly inhibited biofilm formation at MIC/2 (32.5 mg/ml), MIC/4 (16.25 mg/ml), MIC/8 (8.125 mg/ml) and MIC/16 (4.062 mg/ml) (p < 0.0001). The anti-biofilm effect of oleuropein was confirmed by SEM. RT-qPCR indicated significant down regulation of expression genes involved in biofilm formation in Candida albicans (Hwp1, Als3) and Candida glabrata (Epa1, Epa6) as well as Escherichia coli (LuxS, Pfs) genes after culture with a MIC/2 of oleuropein (p < 0.0001).

CONCLUSIONS

The results indicate that oleuropein has antifungal and antibacterial properties that enable it to inhibit or destroy the formation of fungal and bacterial biofilm.

Natural Compounds: A Hopeful Promise as an Antibiofilm Agent Against Candida Species

The biofilm communities of Candida are resistant to various antifungal treatments. The ability of Candida to form biofilms on abiotic and biotic surfaces is considered one of the most important virulence factors of these fungi. Extracellular DNA and exopolysaccharides can lower the antifungal penetration to the deeper layers of the biofilms, which is a serious concern supported by the emergence of azole-resistant isolates and Candida strains with decreased antifungal susceptibility. Since the biofilms' resistance to common antifungal drugs has become more widespread in recent years, more investigations should be performed to develop novel, inexpensive, non-toxic, and effective treatment approaches for controlling biofilm-associated infections. Scientists have used various natural compounds for inhibiting and degrading Candida biofilms. Curcumin, cinnamaldehyde, eugenol, carvacrol, thymol, terpinen-4-ol, linalool, geraniol, cineole, saponin, camphor, borneol, camphene, carnosol, citronellol, coumarin, epigallocatechin gallate, eucalyptol, limonene, menthol, piperine, saponin, α-terpineol, β-pinene, and citral are the major natural compounds that have been used widely for the inhibition and destruction of Candida biofilms. These compounds suppress not only fungal adhesion and biofilm formation but also destroy mature biofilm communities of Candida. Additionally, these natural compounds interact with various cellular processes of Candida, such as ABC-transported mediated drug transport, cell cycle progression, mitochondrial activity, and ergosterol, chitin, and glucan biosynthesis. The use of various drug delivery platforms can enhance the antibiofilm efficacy of natural compounds. Therefore, these drug delivery platforms should be considered as potential candidates for coating catheters and other medical material surfaces. A future goal will be to develop natural compounds as antibiofilm agents that can be used to treat infections by multi-drug-resistant Candida biofilms. Since exact interactions of natural compounds and biofilm structures have not been elucidated, further in vitro toxicology and animal experiments are required. In this article, we have discussed various aspects of natural compound usage for inhibition and destruction of Candida biofilms, along with the methods and procedures that have been used for improving the efficacy of these compounds.

[Metabolomic changes of neonatal sepsis: an exploratory clinical study]

OBJECTIVES

To study the metabolic mechanism of neonatal sepsis at different stages by analyzing the metabolic pathways involving the serum metabolites with significant differences in neonates with sepsis at different time points after admission.

METHODS

A total of 20 neonates with sepsis who were hospitalized in the Department of Neonatology, Hunan Provincial People's Hospital, from January 1, 2019 to January 1, 2020 were enrolled as the sepsis group. Venous blood samples were collected on days 1, 4, and 7 after admission. Ten healthy neonates who underwent physical examination during the same period were enrolled as the control group. Ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry was used for the metabonomic analysis of serum samples to investigate the change in metabolomics in neonates with sepsis at different time points.

RESULTS

On day 1 after admission, the differentially expressed serum metabolites between the sepsis and control groups were mainly involved in the biosynthesis of terpenoid skeleton. For the sepsis group, the differentially expressed serum metabolites between days 1 and 4 after admission were mainly involved in pyruvate metabolism, and those between days 4 and 7 after admission were mainly involved in the metabolism of cysteine and methionine. The differentially expressed serum metabolites between days 1 and 7 after admission were mainly involved in ascorbic acid metabolism.

CONCLUSIONS

The metabolic mechanism of serum metabolites varies at different stages in neonates with sepsis and is mainly associated with terpenoid skeleton biosynthesis, pyruvate metabolism, cysteine/methionine metabolism, and ascorbic acid metabolism.

In vitro effect of farnesol on planktonic cells and dual biofilm formed by Candida albicans and Escherichia coli

Many biofilm studies have focused on axial biofilms, however biofilms in nature and in vivo environment are multi-species. Farnesol is a sesquiterpene alcohol found in many essential oils. This study investigated the in vitro effects of farnesol on planktonic cells and biofilms of Candida albicans and Escherichia coli. The ultrastructural morphology of farnesol treated cells was evaluated by TEM. According to the XTT results, farnesol caused a significant decrease in metabolic activity and scanning electron microscope images confirmed a reduction in the preformed biofilm as a result of farnesol treatment for single species C. albicans and E. coli biofilms. Although farnesol has less effect on dual species biofilm compared to the single species biofilms, its effect on the dual biofilm was found to be stronger than amphotericin B or ampicillin. Further studies are needed to clarify the role of farnesol on fungal-bacterial biofilms.

Synergistic Antibiofilm Effects of Pseudolaric Acid A Combined with Fluconazole against Candida albicans via Inhibition of Adhesion and Yeast-To-Hypha Transition

Candida albicans biofilms are resistant to several clinical antifungal agents. Thus, it is necessary to develop new antibiofilm intervention measures. Pseudolaric acid A (PAA), a diterpenoid mainly derived from the pine bark of Pseudolarix kaempferi, has been reported to have an inhibitory effect on C. albicans. The primary aim of the current study was to investigate the antibiofilm effect of PAA when combined with fluconazole (FLC) and explore the underlying mechanisms. Biofilm activity was assessed by tetrazolium {XTT [2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide salt]} reduction assays. PAA (4 μg/mL) combined with FLC (0.5 μg/mL) significantly inhibited early, developmental, and mature biofilm formation compared with the effect of PAA or FLC alone (P < 0.05). Furthermore, PAA (4 μg/mL) combined with FLC (0.5 μg/mL) produced a 56% reduction in C. albicans biofilm adhesion. The combination of PAA (4 μg/mL) and FLC (0.5 μg/mL) also performed well in inhibiting yeast-to-hypha transition. Transcriptome analysis using RNA sequencing and quantitative reverse transcription PCR indicated that the PAA-FLC combination treatment produced a strong synergistic inhibitory effect on the expression of genes involved in adhesion (ALS1, ALS4, and ALS2) and yeast-to-hypha transition (ECE1, PRA1, and TEC1). Notably, PAA, rather than FLC, may have a primary role in suppressing the expression of ALS1. In conclusion, these findings demonstrate, for the first time, that the combination of PAA and FLC has an improved antibiofilm effect against the formation of C. albicans biofilms by inhibiting adhesion and yeast-to-hypha transition; this may provide a novel therapeutic strategy for treating C. albicans biofilm-associated infection.

IMPORTANCE Biofilms are the primary cause of antibiotic-resistant candida infections associated with medical implants and devices worldwide. Treating biofilm-associated infections is a challenge for clinicians because these infections are intractable and persistent. Candida albicans readily forms extensive biofilms on the surface of medical implants and mucosa. In this study, we demonstrated, for the first time, an inhibitory effect of pseudolaric acid A alone and in combination with fluconazole on C. albicans biofilms. Moreover, pseudolaric acid A in combination with fluconazole exerted an antibiofilm effect through multiple pathways, including inhibition of yeast-to-hypha transition and adhesion. This research not only provides new insights into the synergistic mechanisms of antifungal drug combinations but also brings new possibilities for addressing C. albicans drug resistance.

Plant Preparations and Compounds with Activities against Biofilms Formed by Candida spp

Fungi from the genus Candida are very important human and animal pathogens. Many strains can produce biofilms, which inhibit the activity of antifungal drugs and increase the tolerance or resistance to them as well. Clinically, this process leads to persistent infections and increased mortality. Today, many Candida species are resistant to drugs, including C. auris, which is a multiresistant pathogen. Natural compounds may potentially be used to combat multiresistant and biofilm-forming strains. The aim of this review was to present plant-derived preparations and compounds that inhibit Candida biofilm formation by at least 50%. A total of 29 essential oils and 16 plant extracts demonstrate activity against Candida biofilms, with the following families predominating: Lamiaceae, Myrtaceae, Asteraceae, Fabaceae, and Apiacae. Lavandula dentata (0.045-0.07 mg/L), Satureja macrosiphon (0.06-8 mg/L), and Ziziphora tenuior (2.5 mg/L) have the best antifungal activity. High efficacy has also been observed with Artemisia judaica, Lawsonia inermis, and Thymus vulgaris. Moreover, 69 plant compounds demonstrate activity against Candida biofilms. Activity in concentrations below 16 mg/L was observed with phenolic compounds (thymol, pterostilbene, and eugenol), sesquiterpene derivatives (warburganal, polygodial, and ivalin), chalconoid (lichochalcone A), steroidal saponin (dioscin), flavonoid (baicalein), alkaloids (waltheriones), macrocyclic bisbibenzyl (riccardin D), and cannabinoid (cannabidiol). The above compounds act on biofilm formation and/or mature biofilms. In summary, plant preparations and compounds exhibit anti-biofilm activity against Candida. Given this, they may be a promising alternative to antifungal drugs.

In vitro anticandidal activity and gas chromatography-mass spectrometry (GC-MS) screening of Vitex agnus-castus leaf extracts

Background

Candida infections are becoming more drug resistant; it is necessary to search for alternative medications to treat them. Therefore, the present study estimates the anticandidal activity of Vitex agnus-castus (VA-C) leaf extracts.

Methods

We used the agar well diffusion method to assess the anticandidal activity of three different VA-C leaf extracts (ethanol, methanol, and water) against three Candida species (Candida tropicalis, Candida albicans, and Candida ciferrii). The minimum inhibitory concentration (MIC) was estimated using the two-fold dilution method and the minimum fungicidal concentration (MFC) was determined using the classic pour plate technique. The MFC/MIC ratio was calculated to estimate the microbicidal or microbiostatic activity. A gas chromatography mass spectrometer was used to screen the phytochemicals of the VA-C leaf extracts (ethanol, methanol, and water).

Results

All VA-C extracts ethanol, methanol, and water were significantly inhibited the growth of the test Candida species and the inhibition activity depended on the solvent used and the Candida species. The results showed that C. tropicalis was the most highly inhibited by all extracts followed by C. albicans and C. ciferrii. The MIC values were 12.5–25 µg/ml, and MFC values were 25–100 µg/ml. The ratios of MFC/MIC were two-fold to four-fold which was considered candidacidal activity. Ninety-five phytochemical compounds were identified by the GC-MS assay for the VA-C leaf extracts. The total number of compounds per extract differed. Methanol had 43 compounds, ethanol had 47 compounds, and water had 52 compounds. The highest compound concentrations were: 4,5-Dichloro-1,3-dioxolan-2-one in ethanol and methanol, 1H-Indene, 2,3-dihydro-1,1,2,3,3-pentamethyl in ethanol, Isobutyl 4-hydroxybenzoate in methanol, and Benzoic acid and 4-hydroxy- in water. These phytochemical compounds belong to different bioactive chemical group such as polyphenols, fatty acids, terpenes, terpenoids, steroids, aldehydes, alcohols, and esters, and most of which have anticandidal activity.

Conclusions

VA-C leaf extracts may be useful alternatives to anticandidal drugs, based on their effectiveness against all test Candida species at low concentrations. However, appropriate toxicology screening should be conducted before use.

Erratum: Touil, H.F.Z. et al. Optimum Inhibition of Amphotericin-B-Resistant Candida albicans Strain in Single- and Mixed-Species Biofilms by Candida and Non-Candida Terpenoids. Biomolecules 2020, 10, 342

The authors wish to make the following correction to this paper [1] [...].

Design and synthesis of new drugs inhibitors of Candida albicans hyphae and biofilm formation by upregulating the expression of TUP1 transcription repressor gene

Candida albicans is a common human fungal pathogen that causes disease ranging from superficial to lethal infections. C. albicans grows as budding yeast which can transform into hyphae in response to various environmental or biological stimuli. Although both forms have been associated with virulence, the hyphae form is responsible for the formation of multi-drug resistance biofilm. Here, new compounds were designed to selectively inhibit C. albicans hyphae formation without affecting human cells to afford sufficient safety. The newly designed 5-[3-substitued-4-(4-substituedbenzyloxy)-benzylidene]-2-thioxo-thiazolidin-4-one derivatives, named SR, showed very specific and effective inhibition activity against C. albicans hyphae formation. SR compounds caused hyphae inhibition activity at concentrations 10-40 fold lower than the concentration required to inhibit Candida yeast and bacterial growths. The anti-hyphae inhibition activities of SR compounds were via activation of the hyphae transcription repressor gene, TUP1. Correlation studies between the expression of TUP1 gene and the activity of SR compounds confirmed that the anti-C. albicans activities of SR compounds were via inhibition of hyphae formation. The newly designed SR compounds showed 10-40% haemolytic activity on human erythrocytes when compared to 100% haemolysis by 0.1% triton employed as positive control. Furthermore, theoretical prediction of absorption, distribution, metabolism, excretion, and toxicity (ADMET) of SR compounds confirmed their safety, efficient metabolism and possible oral bioavailability. With the minimal toxicity and significant activity of the newly-designed SR compounds, a future optimization of pharmaceutical formulation may develop a promising inhibitor of hyphal formation not only for C. albicans but also for other TUP1- dependent dimorphic fungal infections.

Essential Oil-Based Design and Development of Novel Anti-Candida Azoles Formulation

Candida is the most common fungal class, causing both superficial and invasive diseases in humans. Although Candida albicans is the most common cause of fungal infections in humans, C. auris is a new emergent serious pathogen causing complications similar to those of C. albicans. Both C. albicans and C. auris are associated with high mortality rates, mainly because of their multidrug-resistance patterns against most available antifungal drugs. Although several compounds were designed against C. albicans, very few or none were tested on C. auris. Therefore, it is urgent to develop novel effective antifungal drugs that can accommodate not only C. albicans, but also other Candida spp., particularly newly emergent one, including C. auris. Inspired by the significant broad-spectrum antifungal activities of the essential oil cuminaldehyde and the reported wide incorporation of azoles in the antifungal drugs, a series of compounds (UoST1-11) was designed and developed. The new compounds were designed to overcome the toxicity of the aldehyde group of cuminaldehyde and benefit from the antifungal selectivity of azoles. The new developed UoST compounds showed significant anti-Candida activities against both Candida species. The best candidate compound, UoST5, was further formulated into polymeric nanoparticles (NPs). The new formula, UoST5-NPs, showed similar activities to the nanoparticles-free drug, while providing only 25% release after 24 h, maintainng prolonged activity up to 48 h and affording no toxicity. In conclusion, new azole formulations with significantly enhanced activities against C. albicans and C. auris, while maintaining prolonged action and no toxicities at lower concentrations, were developed.