Inactivation of genes TEC1 and EFG1 in Candida albicans influences extracellular matrix composition and biofilm morphology

Molecular Determinants Involved in Candida albicans Biofilm Formation and Regulation

Candida albicans is known for its pathogenicity, although it lives within the human body as a commensal member. The commensal nature of C. albicans is well controlled and regulated by the host's immune system as they live in the harmonized microenvironment. However, the development of certain unusual microhabitat conditions (change in pH, co-inhabiting microorganisms' population ratio, debilitated host-immune system) pokes this commensal fungus to transform into a pathogen in such a way that it starts to propagate very rapidly and tries to breach the epithelial barrier to enter the host's systemic circulations. In addition, Candida is infamous as a major nosocomial (hospital-acquired infection) agent because it enters the human body through venous catheters or medical prostheses. The hysterical mode of C. albicans growth builds its microcolony or biofilm, which is pathogenic for the host. Biofilms propose additional resistance mechanisms from host immunity or extracellular chemicals to aid their survival. Differential gene expressions and regulations within the biofilms cause altered morphology and metabolism. The genes associated with adhesiveness, hyphal/pseudo-hyphal growth, persister cell transformation, and biofilm formation by C. albicans are controlled by myriads of cell-signaling regulators. These genes' transcription is controlled by different molecular determinants like transcription factors and regulators. Therefore, this review has focused discussion on host-immune-sensing molecular determinants of Candida during biofilm formation, regulatory descriptors (secondary messengers, regulatory RNAs, transcription factors) of Candida involved in biofilm formation that could enable small-molecule drug discovery against these molecular determinants, and lead to disrupt the well-structured Candida biofilms effectively.

Heterologous expression of the insect SVWC peptide WHIS1 inhibits Candida albicans invasion into A549 and HeLa epithelial cells

Candida albicans (C. albicans), a microbe commonly isolated from Candida vaginitis patients with vaginal tract infections, transforms from yeast to hyphae and produces many toxins, adhesins, and invasins, as well as C. albicans biofilms resistant to antifungal antibiotic treatment. Effective agents against this pathogen are urgently needed. Antimicrobial peptides (AMPs) have been used to cure inflammation and infectious diseases. In this study, we isolated whole housefly larvae insect SVWC peptide 1 (WHIS1), a novel insect single von Willebrand factor C-domain protein (SVWC) peptide from whole housefly larvae. The expression pattern of WHIS1 showed a response to the stimulation of C. albicans. In contrast to other SVWC members, which function as antiviral peptides, interferon (IFN) analogs or pathogen recognition receptors (PRRs), which are the prokaryotically expressed MdWHIS1 protein, inhibit the growth of C. albicans. Eukaryotic heterologous expression of WHIS1 inhibited C. albicans invasion into A549 and HeLa cells. The heterologous expression of WHIS1 clearly inhibited hyphal formation both extracellularly and intracellularly. Furthermore, the mechanism of WHIS1 has demonstrated that it downregulates all key hyphal formation factors (ALS1, ALS3, ALS5, ECE1, HWP1, HGC1, EFG1, and ZAP1) both extracellularly and intracellularly. These data showed that heterologously expressed WHIS1 inhibits C. albicans invasion into epithelial cells by affecting hyphal formation and adhesion factor-related gene expression. These findings provide new potential drug candidates for treating C. albicans infection.

Mechanisms of antifungal resistance and developments in alternative strategies to combat Candida albicans infection

Candida albicans is a commensal fungus that infects the humans and becomes an opportunistic pathogen particularly in immuno-compromised patients. Among the Candida genus, yeast C. albicans is the most frequently incriminated species and is responsible for nearly 50-90% of human candidiasis, with vulvovaginal candidiasis alone, affecting about 75% of the women worldwide. One of the significant virulence traits in C. albicans is its tendency to alternate between the yeast and hyphae morphotypes, accounting for the development of multi-drug resistance in them. Thus, a thorough comprehension of the decision points and genes controlling this transition is necessary, to understand the pathogenicity of this, naturally occurring, pernicious fungus. Additionally, the formation of C. albicans biofilm is yet another pathogenesis trait and a paramount cause of invasive candidiasis. Since 1980 and in 90 s, wide spread use of immune-suppressing therapies and over prescription of fluconazole, a drug used to treat chronic fungal infections, triggered the emergence of novel anti-fungal drug development. Thus, this review thoroughly elucidates the diseases associated with C. albicans infection as well as the anti-fungal resistance mechanism associated with them and identifies the emerging therapeutic agents, along with a rigorous discussion regarding the future strategies that can possibly be adopted for the cure of this deleterious pathogen.

Antibiofilm Activity and Biocompatibility of Temporin-SHa: A Promising Antimicrobial Peptide for Control of Fluconazole-Resistant Candida albicans

The aim of the study was to investigate the effect of antimicrobial peptides (AMPs) Hylin-a1, KR-12-a5, and Temporin-SHa in Candida albicans as well as the biocompatibility of keratinocytes spontaneously immortalized (NOK-si) and human gingival fibroblasts (FGH) cells. Initially, the susceptible (CaS-ATCC 90028) and fluconazole-resistant (CaR-ATCC 96901) C. albicans strains were grown to evaluate the effect of each AMP in planktonic culture, biofilm, and biocompatibility on oral cells. Among the AMPs evaluated, temporin-SHa showed the most promising results. After 24 h of Temporin-SHa exposure, the survival curve results showed that CaS and CaR suspensions reduced 72% and 70% of cell viability compared to the control group. The minimum inhibitory/fungicide concentrations (MIC and MFC) showed that Temporin-SHa was able to reduce ≥50% at ≥256 µg/mL for both strains. The inhibition of biofilm formation, efficacy against biofilm formation, and total biomass assays were performed until 48 h of biofilm maturation, and Temporin-SHa was able to reduce ≥50% of CaS and CaR growth. Furthermore, Temporin-SHa (512 µg/mL) was classified as non-cytotoxic and slightly cytotoxic for NOK-si and FGH, respectively. Temporin-SHa demonstrated an anti-biofilm effect against CaS and CaR and was biocompatible with NOK-si and FGH oral cells in monolayer.

Transcription Factors Tec1 and Tec2 Play Key Roles in the Hyphal Growth and Virulence of Mucor lusitanicus Through Increased Mitochondrial Oxidative Metabolism

Mucormycosis is a lethal and difficult-to-treat fungal infection caused by fungi of the order Mucorales. Mucor lusitanicus, a member of Mucorales, is commonly used as a model to understand disease pathogenesis. However, transcriptional control of hyphal growth and virulence in Mucorales is poorly understood. This study aimed to investigate the role of Tec proteins, which belong to the TEA/ATTS transcription factor family, in the hyphal development and virulence of M. lusitanicus. Unlike in the genome of Ascomycetes and Basidiomycetes, which have a single Tec homologue, in the genome of Mucorales, two Tec homologues, Tec1 and Tec2, were found, except in that of Phycomyces blakesleeanus, with only one Tec homologue. tec1 and tec2 overexpression in M. lusitanicus increased mycelial growth, mitochondrial content and activity, expression of the rhizoferrin synthetase-encoding gene rfs, and virulence in nematodes and wax moth larvae but decreased cAMP levels and protein kinase A (PKA) activity. Furthermore, tec1- and tec2-overexpressing strains required adequate mitochondrial metabolism to promote the virulent phenotype. The heterotrimeric G beta subunit 1-encoding gene deletant strain (Δgpb1) increased cAMP-PKA activity, downregulation of both tec genes, decreased both virulence and hyphal development, but tec1 and tec2 overexpression restored these defects. Overexpression of allele-mutated variants of Tec1(S332A) and Tec2(S168A) in the putative phosphorylation sites for PKA increased both virulence and hyphal growth of Δgpb1. These findings suggest that Tec homologues promote mycelial development and virulence by enhancing mitochondrial metabolism and rhizoferrin accumulation, providing new information for the rational control of the virulent phenotype of M. lusitanicus.

Chitosan microparticles loaded with essential oils inhibit duo-biofilms of Candida albicans and Streptococcus mutans

OBJECTIVE

Oral candidiasis is a common fungal infection that affects the oral mucosa, and happens when Candida albicans interacts with bacteria in the oral microbiota, such as Streptococcus mutans, causing severe early childhood caries. C. albicans and S. mutans mixed biofilms are challenging to treat with conventional antimicrobial therapies, thus, new anti-infective drugs are required. This study aimed to test a drug delivery system based on chitosan microparticles loaded with geranium and lemongrass essential oils to inhibit C. albicans and S. mutans mixed biofilms.

METHODOLOGY

Chitosan microparticles loaded with essential oils (CM-EOs) were obtained by spray-drying. Susceptibility of planktonic were performed according CLSI at 4 to 2,048 µg/mL. Mixed biofilms were incubated at 37ºC for 48 h and exposed to CM-EOs at 256 to 4,096 µg/mL. The antimicrobial effect was evaluated using the MTT assay, with biofilm architectural changes analyzed by scanning electron microscopy. RAW 264.7 cell was used to evaluate compound cytotoxicity.

RESULTS

CM-EOs had better planktonic activity against C. albicans than S. mutans. All samples reduced the metabolic activity of mixed C. albicans and S. mutans biofilms, with encapsulated oils showing better activity than raw chitosan or oils. The microparticles reduced the biofilm on the slides. The essential oils showed cytotoxic effects against RAW 264.7 cells, but encapsulation into chitosan microparticles decreased their toxicity.

CONCLUSION

This study demonstrates that chitosan loaded with essential oils may provide an alternative method for treating diseases caused by C. albicans and S. mutans mixed biofilm, such as dental caries.

Shikonin Inhibits Candida albicans Biofilms via the Ras1-cAMP-Efg1 Signalling Pathway

Objective

To investigate the influence of shikonin (SK) on the formation of Candida albicans biofilms and discuss the possible mechanism.

Methods

The inhibition of the formation of C. albicans biofilms by SK was observed by scanning electron microscopy. A silicone film method and a water-hydrocarbon two-phase assay were performed to investigate the effects of SK on cell adhesion. Real-time reverse-transcription polymerase chain reaction was used to analyse the expression of genes related to cell adhesion and Ras1-cyclic adenosine monophosphate (cAMP) - enhanced filamentous growth protein 1 (Efg1) signalling pathway. Finally, the level of cAMP in C. albicans was detected and exogenous cAMP rescue experiment was conducted.

Results

The results showed that SK could destroy the typical three-dimensional structure of the biofilms, inhibit cell surface hydrophobicity and cell adhesion, downregulate the expression of Ras1-cAMP-Efg1 signalling pathway-related genes (ECE1, HWP1, ALS3, RAS1, CYR1, EFG1 and TEC1) and effectively reduce the production of key messenger cAMP in the Ras1-cAMP-Efg1 pathway. Meanwhile, exogenous cAMP reversed the inhibitory effect of SK on biofilms formation.

Conclusion

Our results suggest that SK exhibits potential anti-C. albicans biofilms effects related to the inhibition of Ras1-cAMP-Efg1 pathway.

Zerumbone Disturbs the Extracellular Matrix of Fluconazole-Resistant Candida albicans Biofilms

This study assessed the effect of zerumbone (ZER) against fluconazole-resistant (CaR) and -susceptible Candida albicans (CaS) biofilms and verified the influence of ZER on extracellular matrix components. Initially, to determine the treatment conditions, the minimum inhibitory concentration (MIC), the minimum fungicidal concentration (MFC) and the survival curve were evaluated. Biofilms were formed for 48 h and exposed to ZER at concentrations of 128 and 256 µg/mL for 5, 10 and 20 min (n = 12). One group of biofilms did not receive the treatment in order to monitor the effects. The biofilms were evaluated to determine the microbial population (CFU/mL), and the extracellular matrix components (water-soluble polysaccharides (WSP), alkali-soluble polysaccharides (ASPs), proteins and extracellular DNA (eDNA), as well as the biomass (total and insoluble) were quantified. The MIC value of ZER for CaS was 256 μg/mL, and for CaR, it was 64 μg/mL. The survival curve and the MFC value coincided for CaS (256 μg/mL) and CaR (128 μg/mL). ZER reduced the cellular viability by 38.51% for CaS and by 36.99% for CaR. ZER at 256 µg/mL also reduced the total biomass (57%), insoluble biomass (45%), WSP (65%), proteins (18%) and eDNA (78%) of CaS biofilms. In addition, a reduction in insoluble biomass (13%), proteins (18%), WSP (65%), ASP (10%) and eDNA (23%) was also observed in the CaR biofilms. ZER was effective against fluconazole-resistant and -susceptible C. albicans biofilms and disturbed the extracellular matrix.

Physiological, epigenetic, and proteomic responses in Pfaffia glomerata growth in vitro under salt stress and 5-azacytidine

Plants adjust their complex molecular, biochemical, and metabolic processes to overcome salt stress. Here, we investigated the proteomic and epigenetic alterations involved in the morphophysiological responses of Pfaffia glomerata, a medicinal plant, to salt stress and the demethylating agent 5-azacytidine (5-azaC). Moreover, we investigated how these changes affected the biosynthesis of 20-hydroxyecdysone (20-E), a pharmacologically important specialized metabolite. Plants were cultivated in vitro for 40 days in Murashige and Skoog medium supplemented with NaCl (50 mM), 5-azaC (25 μM), and NaCl + 5-azaC. Compared with the control (medium only), the treatments reduced growth, photosynthetic rates, and photosynthetic pigment content, with increase in sucrose, total amino acids, and proline contents, but a reduction in starch and protein. Comparative proteomic analysis revealed 282 common differentially accumulated proteins involved in 87 metabolic pathways, most of them related to amino acid and carbohydrate metabolism, and specialized metabolism. 5-azaC and NaCl + 5-azaC lowered global DNA methylation levels and 20-E content, suggesting that 20-E biosynthesis may be regulated by epigenetic mechanisms. Moreover, downregulation of a key protein in jasmonate biosynthesis indicates the fundamental role of this hormone in the 20-E biosynthesis. Taken together, our results highlight possible regulatory proteins and epigenetic changes related to salt stress tolerance and 20-E biosynthesis in P. glomerata, paving the way for future studies of the mechanisms involved in this regulation.

The Antimicrobial Peptide AMP-17 Derived from Musca domestica Inhibits Biofilm Formation and Eradicates Mature Biofilm in Candida albicans

The biofilm formation of C. albicans represents a major virulence factor during candidiasis. Biofilm-mediated drug resistance has necessitated the search for a new antifungal treatment strategy. In our previous study, a novel antimicrobial peptide named AMP-17 derived from Musca domestica was confirmed to have significant antifungal activity and suppress hyphal growth greatly in C. albicans. In the current work, we aimed to investigate the antibiofilm property of AMP-17 in C. albicans and explore the underlying mechanism. An antifungal susceptibility assay showed that AMP-17 exerted a strong inhibitory efficacy on both biofilm formation and preformed biofilms in C. albicans. Furthermore, AMP-17 was found to block the yeast-to-hypha transition and inhibit the adhesion of biofilm cells with a reduction in cellular surface hydrophobicity. A morphological analysis revealed that AMP-17 indeed suppressed typical biofilm formation and damaged the structures of the preformed biofilm. The RNA-seq showed that the MAPK pathway, biosynthesis of antibiotics, and essential components of the cell were mainly enriched in the biofilm-forming stage, while the citrate cycle (TCA cycle), phenylamine metabolism, and propanoate metabolism were enriched after the biofilm matured. Moreover, the co-expressed DEGs in the two pairwise comparisons highlighted the terms of transmembrane transporter activity, regulation of filamentation, and biofilm formation as important roles in the antibiofilm effect of AMP-17. Additionally, qRT-PCR confirmed that the level of the genes involved in cell adhesion, filamentous growth, MAPK, biofilm matrix, and cell dispersal was correspondingly altered after AMP-17 treatment. Overall, our findings reveal the underlying antibiofilm mechanisms of AMPs in C. albicans, providing an interesting perspective for the development of effective antifungal agents with antibiofilm efficacy in Candida spp.

Pathogenesis in Pseudomonas aeruginosa PAO1 Biofilm-Associated Is Dependent on the Pyoverdine and Pyocyanin Siderophores by Quorum Sensing Modulation

Pseudomonas aeruginosa is an opportunistic pathogenic bacterium for humans, animals, and plants, through producing different molecular factors such as biofilm, siderophores, and other virulence factors which favor bacterial establishment and infection in the host. In P. aeruginosa PAO1, the production of these factors is regulated by the bacterial quorum sensing (QS) mechanisms. From them, siderophores are involved in iron acquisition, transport, and homeostasis. They are also considered some of the main virulence factors in P. aeruginosa; however, detailed mechanisms to induce bacterial pathogenesis are poorly understood. In this work, through reverse genetics, we evaluated the function of bacterial pathogenesis in the pvd cluster genes, which are required for synthesizing the siderophore pyoverdine (PVD). Single pvdI, pvdJ, pvdL, and double mutant strains were analyzed, and contrary to expected, the pvdL and pvdI mutations increased the concentration of PVD and other phenazines, such as pyocyanin (PYO) and phenazine-1-carboxylic acid (PCA) and also an increased biofilm production and morphology depending on the autoinducer 2-alkyl-4-quinolone (PQS) and the QS molecules acyl-homoserine lactones. Consequently, in the in vivo pathogenicity model of Caenorhabditis elegans, the mutations in pvdI, pvdJ, and pvdL increased the survival of the worms exposed to supernatants or biofilms of the bacterial cultures. However, the double mutant pvdI/pvdJ increased its toxicity in agreeing with the biofilm production, PVD, PYO, and PCA. The findings indicate that the mutations in pvd genes encode non-ribosomal peptide synthetases impacted the biofilm's structure, but suppressively also of the phenazines, confirming that the siderophores contribute to the bacterial establishment and pathogenicity of P. aeruginosa PAO1.

The Role of Glycoside Hydrolases in S. gordonii and C. albicans Interactions

Candida albicans can coaggregate with Streptococcus gordonii and cocolonize in the oral cavity. Saliva provides a vital microenvironment for close interactions of oral microorganisms. However, the level of fermentable carbohydrates in saliva is not sufficient to support the growth of multiple species. Glycoside hydrolases (GHs) that hydrolyze glycoproteins are critical for S. gordonii growth in low-fermentable-carbohydrate environments such as saliva. However, whether GHs are involved in the cross-kingdom interactions between C. albicans and S. gordonii under such conditions remains unknown. In this study, C. albicans and S. gordonii were cocultured in heart infusion broth with a low level of fermentable carbohydrate. Planktonic growth, biofilm formation, cell aggregation, and GH activities of monocultures and cocultures were examined. The results revealed that the planktonic growth of cocultured S. gordonii in a low-carbohydrate environment was elevated, while that of cocultured C. albicans was reduced. The biomass of S. gordonii in dual-species biofilms was higher than that of monocultures, while that of cocultured C. albicans was decreased. GH activity was observed in S. gordonii, and elevated activity of GHs was detected in S. gordonii-C. albicans cocultures, with elevated expression of GH-related genes of S. gordonii. By screening a mutant library of C. albicans, we identified a tec1Δ/Δ mutant strain that showed reduced ability to promote the growth and GH activities of S. gordonii compared with the wild-type strain. Altogether, the findings of this study demonstrate the involvement of GHs in the cross-kingdom metabolic interactions between C. albicans and S. gordonii in an environment with low level of fermentable carbohydrates. IMPORTANCE Cross-kingdom interactions between Candida albicans and oral streptococci such as Streptococcus gordonii have been reported. However, their interactions in a low-fermentable-carbohydrate environment like saliva is not clear. The current study revealed glycoside hydrolase-related cross-kingdom communications between S. gordonii and C. albicans under the low-fermentable-carbohydrate condition. We demonstrate that C. albicans can promote the growth and metabolic activities of S. gordonii by elevating the activities of cell-wall-anchored glycoside hydrolases of S. gordonii. C. albicans gene TEC1 is critical for this cross-kingdom metabolic communication.

DNase enhances photodynamic therapy against fluconazole-resistant Candida albicans biofilms

OBJECTIVE

This study evaluated the effectiveness of DNase I combined with antimicrobial photodynamic therapy, mediated by Photodithazine^® and light-emitting diode light, against biofilms formed by a fluconazole-resistant Candida albicans strain (ATCC 96901) and two clinical isolates (R14 and R70).

MATERIALS AND METHODS

Biofilms were grown for 48 h and exposed to DNase for 5 min, followed by application of a photosensitizer (P) and light (L), either singly or combined (P+L+, P-L+, P+L-, P-L-, P-L-DNase, P+L+DNase, P+L-DNase, and P-L+DNase; n = 12). Biofilm analysis included quantification of extracellular matrix components (water-soluble and insoluble proteins and polysaccharides, and extracellular DNA), and biomass (total and insoluble), as well as enumeration of colony-forming units. The data were analyzed using three-way analysis of variance with Bonferroni's post-hoc test.

RESULTS

The DNase treatment combined with aPDT showed a reduction of 1.92, 1.65, and 1.29 log₁₀ of cell viability compared with untreated controls for ATCC 96901, R14, and R70 strains, respectively. It also reduced extracellular matrix contents of water-soluble polysaccharides (36.3%) and extracellular DNA (72.3%), as well as insoluble biomass content (43.3%).

CONCLUSION

The three strains showed similar behavior when treated with DNase, and the extracellular matrix components were affected, improving the effectiveness of antimicrobial photodynamic therapy.

Lactobacillus casei reduces the extracellular matrix components of fluconazole-susceptible Candida albicans biofilms

Fluconazole-sensitive (CaS) and -resistant (CaR) C. albicans were grown as single-species and dual-species biofilms with Lactobacillus casei (Lc) and Lactobacillus rhamnosus (Lr). Single-species Lc and Lr were also evaluated. Biofilm analysis included viable plate counts, the extracellular matrix components, biomass, and structural organization. Lc reduced the viability of CaS, water-soluble polysaccharides, and eDNA in CaS + Lc biofilm. Lc biofilm presented more eDNA than CaS. The total biomass of CaS + Lc biofilm was higher than the single-species biofilms. The viability of Lc and Lr was reduced by CaR dual-species biofilms. The total and insoluble biomass in CaS + Lr was higher than in single-species CaS biofilms. Lc hindered the growth of CaS, and their association hampered matrix components linked to the structural integrity of the biofilm. These findings allow understanding of how the implementation of probiotics influences the growth of C. albicans biofilms and thereby helps with the development of novel approaches to control these biofilms.

Impeding Virulence of Candida albicans by Candesartan and Domperidone

Candida albicans is the most common human fungal pathogen that has developed extensive virulence factors which allows successful colonization and infection of the host. Anti-virulence agents can alleviate the pathogenesis of fungi and help the immune system to eradicate them easily. This study aimed to explore the anti-virulence effect of domperidone and candesartan against C. albicans standard strain. Sub-inhibitory concentrations (1/4 and 1/8 of minimum inhibitory concentration) of domperidone and candesartan significantly inhibited the virulence factors hemolysin, lipase, protease, phospholipase, and bioflim formation. It was found that candesartan inhibited biofilm formation by 60.48-67.91%, hemolysin activity (61.21-74.14%), phospholipase activity (40-49.67%), lipase activity (58.97-73%), and protease activity (52.63%), while domperidone was found to inhibit biofilm formation by 70.54-77.49%, hemolysin activity (64.84-69.84%), phospholipase activity (49.67-60%), lipase activity (50-54.87%), and protease activity (52.63-57.9%). Quantitative real time-PCR confirmed the anti-virulence activity of domperidone and candesartan as both drugs significantly reduce the expression of the virulence genes SAP2, SAP6, PLB1, PLB2, LIP4, LIP5. In conclusion, domperidone and candesartan could serve as anti-virulence agents for treatment of C. albicans infections.

Candida biofilm matrix as a resistance mechanism against photodynamic therapy

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) efficiency on Candida albicans is recognized in free-floating cultures. Though, the lack of aPDT effectiveness against C. albicans organized in biofilms is still unclear. This study aimed to explore the role of the extracellular matrix (ECM) in the protection against aPDT in C. albicans biofilms.

METHODS

C. albicans SN 425 wild-type and two mutant strains CNJ 2302; Δ/Δefg1 and CJN 2330; Δ/Δtec1 (ECM deficient) were used. Biofilms were grown on 24-well plates and exposed twice-daily to aPDT with 44 μM toluidine blue-O (TBO) for 5 min followed by red light (635 nm) for 1 min (87.6 J/cm²) or 2 min (175.2 J/cm²). Application of just TBO, light, 0.12% chlorhexidine, and ultrapure water were used as controls. After 48 h, biofilms were assessed for dry-weight (DW), colony forming units (CFU), extracellular DNA (eDNA), soluble and insoluble protein (SP/IP), water-insoluble (alkali-soluble) polysaccharide (ASP), water-soluble polysaccharides (WSP), and confocal scanning laser microscopy.

RESULTS

The strains with ECM deficient were affected by aPDT. For the mutant strain Δ/Δefg1, aPDT significantly reduced CFU, ASP, DW, eDNA, WSP and IP when compared to NC (p<0.001) and for the Δ/Δtec1, aPDT significantly reduced CFU, eDNA, IP and SP. Whereas CFU, DW, ASP of the wild-type strain biofilms were not reduced (p>0.05).

CONCLUSIONS

C. albicans strains with reduced ECM compounds were more sensitive to aPDT suggesting that the ECM may have a significant protection role from aPDT in C. albicans biofilms.

From the first touch to biofilm establishment by the human pathogen Candida glabrata: a genome-wide to nanoscale view

Candida glabrata is an opportunistic pathogen that adheres to human epithelial mucosa and forms biofilm to cause persistent infections. In this work, Single-cell Force Spectroscopy (SCFS) was used to glimpse at the adhesive properties of C. glabrata as it interacts with clinically relevant surfaces, the first step towards biofilm formation. Following a genetic screening, RNA-sequencing revealed that half of the entire transcriptome of C. glabrata is remodeled upon biofilm formation, around 40% of which under the control of the transcription factors CgEfg1 and CgTec1. Using SCFS, it was possible to observe that CgEfg1, but not CgTec1, is necessary for the initial interaction of C. glabrata cells with both abiotic surfaces and epithelial cells, while both transcription factors orchestrate biofilm maturation. Overall, this study characterizes the network of transcription factors controlling massive transcriptional remodelling occurring from the initial cell-surface interaction to mature biofilm formation.

Statherin-derived peptides as antifungal strategy against Candida albicans

OBJECTIVE

The aim of this in vitro study was to evaluate the effect of statherin and its naturally occurring peptides (DR9-2, DR9, GE-12, IT-32, GQ-19, IP-18) on Candida albicans metabolism and biofilm development.

DESIGN

After the killing assay, a peptide pellicle was formed on the bottom of a polystyrene plate at the IC₅₀ of each peptide. Over the peptide pellicle, Candida albicans biofilm (48 h) was grown. The peptides antimicrobial activity after the peptides treatment was evaluated by alamarBlue, total biofilm biomass and colony forming units (CFU) counting.

RESULTS

The pellicle with statherin and the peptides (DR9-2, DR9, GE-12, IP-18, GQ-19) was able to reduce he viability of Candida albicans compared to the negative control. They also decreased cell proliferation by 20 % and total biomass. IT-32 showed the highest reduction in cell proliferation and biomass, which was similar to the positive control, histatin 5.

CONCLUSIONS

These results suggest that the naturally occuring peptides from statherin are able to decrease Candida albicans colonization and biofilm proliferation.

Candida albicans biofilms and polymicrobial interactions

Candida albicans is a common fungus of the human microbiota. While generally a harmless commensal in healthy individuals, several factors can lead to its overgrowth and cause a range of complications within the host, from localized superficial infections to systemic life-threatening disseminated candidiasis. A major virulence factor of C. albicans is its ability to form biofilms, a closely packed community of cells that can grow on both abiotic and biotic substrates, including implanted medical devices and mucosal surfaces. These biofilms are extremely hard to eradicate, are resistant to conventional antifungal treatment and are associated with high morbidity and mortality rates, making biofilm-associated infections a major clinical challenge. Here, we review the current knowledge of the processes involved in C. albicans biofilm formation and development, including the central processes of adhesion, extracellular matrix production and the transcriptional network that regulates biofilm development. We also consider the advantages of the biofilm lifestyle and explore polymicrobial interactions within multispecies biofilms that are formed by C. albicans and selected microbial species.

Irradiance-driven 20-hydroxyecdysone production and morphophysiological changes in Pfaffia glomerata plants grown in vitro

Pfaffia glomerata possesses potential pharmacological and medicinal properties, mainly owing to the secondary metabolite 20-hydroxyecdysone (20E). Increasing production of biomass and 20E is important for industrial purposes. This study aimed to evaluate the influence of irradiance on plant morphology and production of 20E in P. glomerata grown in vitro. Nodal segments of accessions 22 and 43 (Ac22 and Ac43) were inoculated in culture medium containing MS salts and vitamins. Cultures were maintained at 25 ± 2 °C under a 16-h photoperiod and subjected to irradiance treatments of 65, 130, and 200 μmol m^-2 s^-1 by fluorescent lamps. After 30 days, growth parameters, pigment content, stomatal density, in vitro photosynthesis, metabolites content, and morphoanatomy were assessed. Notably, Ac22 plants exhibited 10-fold higher 20E production when cultivated at 200 μmol m^-2 s^-1 than at 65 μmol m^-2 s^-1, evidencing the importance of light quantity for the accumulation of this metabolite. 20E production was twice as high in Ac22 as in Ac43 plants although both accessions responded positively to higher irradiance. Growth under 200 μmol m^-2 s^-1 stimulated photosynthesis and consequent biomass accumulation, but lowered carotenoids and anthocyanins. Furthermore, increasing irradiance enhanced the number of palisade and spongy parenchyma cells, enhancing the overall growth of P. glomerata. Graphical abstract.

Sodium New Houttuyfonate Inhibits Candida albicans Biofilm Formation by Inhibiting the Ras1-cAMP-Efg1 Pathway Revealed by RNA-seq

Here, we aim to investigate the antifungal effect and mechanism of action of sodium new houttuyfonate (SNH) against Candida albicans. Microdilution analysis results showed that SNH possesses potent inhibitory activity against C. albicans SC5314, with a MIC₈₀ of 256 μg/mL. Furthermore, we found that SNH can effectively inhibit the initial adhesion of C. albicans. Inverted microscopy, crystal violet staining, scanning electron microscopy and confocal laser scanning microscopy results showed that morphological changes during the transition from yeast to hypha and the biofilm formation of C. albicans are repressed by SNH treatment. We also found that SNH can effectively inhibit the biofilm formation of clinical C. albicans strains (Z103, Z3044, Z1402, and Z1407) and SNH in combination with fluconazole, berberine chloride, caspofungin and itraconazole antifungal agents can synergistically inhibit the biofilm formation of C. albicans. Eukaryotic transcriptome sequencing and qRT-PCR results showed that SNH treatment resulted in significantly down-regulated expression in several biofilm formation related genes in the Ras1-cAMP-Efg1 pathway (ALS1, ALA1, ALS3, EAP1, RAS1, EFG1, HWP1, and TEC1) and significantly up-regulated expression in yeast form-associated genes (YWP1 and RHD1). We also found that SNH can effectively reduce the production of key messenger cAMP in the Ras1-cAMP-Efg1 pathway. Furthermore, using Galleria mellonella as an in vivo model we found that SNH can effectively treat C. albicans infection in vivo. Our presented results suggest that SNH exhibits potential antibiofilm effects related to inhibiting the Ras1-cAMP-Efg1 pathway in the biofilm formation of C. albicans.

Fungistatic Action of N-Acetylcysteine on Candida albicans Biofilms and Its Interaction with Antifungal Agents

Therapies targeted to fungal biofilms, mainly against the matrix, and therapies that do not induce microbial resistance are relevant. N-acetylcysteine (NAC), a mucolytic agent, has shown antimicrobial action. This study evaluated the effect of NAC against fluconazole-susceptible (CaS) and -resistant (CaR) Candida albicans. The susceptibility of planktonic cultures to NAC, the effect of NAC on biofilms and their matrix, the interaction of NAC with antifungal agents, and confocal microscopy were evaluated. Data were analyzed descriptively and by the ANOVA/Welch and Tukey/Gomes-Howell tests. The minimum inhibitory concentration (MIC) of NAC was 25 mg/mL for both strains. NAC significantly reduced the viability of both fungal strains. Concentrations higher than the MIC (100 and 50 mg/mL) reduced the viability and the biomass. NAC at 12.5 mg/mL increased the fungal viability. NAC also reduced the soluble components of the biofilm matrix, and showed synergism with caspofungin against planktonic cultures of CaS, but not against biofilms. Confocal images demonstrated that NAC reduced the biofilm thickness and the fluorescence intensity of most fluorochromes used. High concentrations of NAC had similar fungistatic effects against both strains, while a low concentration showed the opposite result. The antibiofilm action of NAC was due to its fungistatic action.

Mechanism of Candida pathogenesis: revisiting the vital drivers

Candida is the most implicated fungal pathogen in the clinical setting. Several factors play important roles in the pathogenesis of Candida spp. Multiple transcriptional circuits, morphological and phenotypic switching, biofilm formation, tissue damaging extracellular hydrolytic enzymes, metabolic flexibility, genome plasticity, adaptation to environmental pH fluctuation, robust nutrient acquisition system, adherence and invasions (mediated by adhesins and invasins), heat shock proteins (HSPs), cytolytic proteins, escape from phagocytosis, evasion from host immune system, synergistic coaggregation with resident microbiota, resistance to antifungal agents, and the ability to efficiently respond to multiple stresses are some of the major pathogenic determinants of Candida species. The existence of multiple connections, in addition to the interactions and associations among all of these factors, are distinctive features that play important roles in the establishment of Candida infections. This review describes all the underlying factors and mechanisms involved in Candida pathogenesis by evaluating pathogenic determinants of Candida species. It reinforces the already available pool of data on the pathogenesis of Candida species by providing a clear and simplified understanding of the most important factors implicated in the pathogenesis of Candida species. The Candida pathogenesis network, an illustration linking all the major determinants of Candida pathogenesis, is also presented. Taken together, they will further improve our current understanding of how these factors modulate virulence and consequent infection(s). Development of new antifungal drugs and better therapeutic approaches to candidiasis can be achieved in the near future with continuing progress in the understanding of the mechanisms of Candida pathogenesis.

Screening the Drug:H+ Antiporter Family for a Role in Biofilm Formation in Candida glabrata

Biofilm formation and drug resistance are two key pathogenesis traits exhibited by Candida glabrata as a human pathogen. Interestingly, specific pathways appear to be in the crossroad between the two phenomena, making them promising targets for drug development. In this study, the 10 multidrug resistance transporters of the Drug:H⁺ Antiporter family of C. glabrata were screened for a role in biofilm formation. Besides previously identified players in this process, namely CgTpo1_2 and CgQdr2, two others are shown to contribute to biofilm formation: CgDtr1 and CgTpo4. The deletion of each of these genes was found to lead to lower biofilm formation, in both SDB and RPMI media, while their expression was found to increase during biofilm development and to be controlled by the transcription factor CgTec1, a predicted key regulator of biofilm formation. Additionally, the deletion of CgDTR1, CgTPO4, or even CgQDR2 was found to increase plasma membrane potential and lead to decreased expression of adhesin encoding genes, particularly CgALS1 and CgEPA1, during biofilm formation. Although the exact role of these drug transporters in biofilm formation remains elusive, our current model suggests that their control over membrane potential by the transport of charged molecules, may affect the perception of nutrient availability, which in turn may delay the triggering of adhesion and biofilm formation.

Inhibition of adhesion-specific genes by Solidago virgaurea extract causes loss of Candida albicans biofilm integrity

AIMS

Candida albicans biofilms are commonly associated with severe oral infections. We previously discovered that a crude extract from the Solidago virgaurea plant (SV extract) was a potent inhibitor of C. albicans biofilm formation. Here, we further investigate the mechanisms underlying C. albicans biofilm inhibition by the SV extract.

METHODS AND RESULTS

The SV extract was shown to inhibit laboratory and clinical C. albicans isolates adherence and hyphal transition on inert support and epithelial human cells, without affecting viability and growth of planktonic yeasts. Interestingly, RT-PCR-based experiments demonstrated that some key genes involved in adhesion and hyphal morphological switch (e.g. Hwp1p, Ece1p, Als3p) were strongly down-regulated by the SV extract. Moreover, antimicrobial synergy testing (checkerboard assay) demonstrated that antifungal effects of miconazole, nystatin or a common antiseptic mouthwash were synergistically improved when used in combination with the SV extract.

CONCLUSIONS

The SV extract prevents C. albicans biofilm formation through direct inhibition of key adherence and hyphae-associated genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Biofilm is considered as a key virulence factor of C. albicans infection. Our discovery of an inhibitor specifically acting on genes involved in biofilm formation paves the way for the future development of a new class of antifungal product.

Biofilms and vulvovaginal candidiasis

Candida species, including C. albicans, are part of the mucosal flora of most healthy women, and inhabit the gastrointestinal and genitourinary tracts. Under favourable conditions, they can colonize the vulvovaginal mucosa, giving rise to symptomatic vulvovaginal candidiasis (VVC). The mechanism by which Candida spp. produces inflammation is unknown. Both, the blastoconidia and the pseudohyphae are capable of destroying the vaginal epithelium by direct invasion. Although the symptoms are not always related to the fungal burden, in general, VVC is associated with a greater number of yeasts and pseudohyphae. Some years ago, C. albicans was the species most frequently involved in the different forms of VVC. However, infections by different species have emerged during the last two decades producing an increase in causative species of VVC such as C. glabrata, C. parapsilosis, C. krusei and C. tropicalis. Candida species are pathogenic organisms that have two forms of development: planktonic and biofilm. A biofilm is defined as a community of microorganisms attached to a surface and encompassed by an extracellular matrix. This form of presentation gives microorganisms greater resistance to antifungal agents. This review, about Candia spp. with a special emphasis on Candida albicans discusses specific areas such as biofilm structure and development, cell morphology and biofilm formation, biofilm-associated gene expression, the cell surface and adherence, the extracellular matrix, biofilm metabolism, and biofilm drug resistance in vulvovaginitis biofilms as an important virulence factor in fungi.

Twice-daily red and blue light treatment for Candida albicans biofilm matrix development control

Phototherapy has been proposed as a direct means of affecting local bacterial infections. However, the use of phototherapy to prevent fungal biofilm development has received comparatively less attention. This study aimed to determine the effects of red light treatment and blue light treatment, without a photosensitizer, on the development of Candida albicans biofilm. During the development of 48-h biofilms of C. albicans SN 425 (n = 10), the biofilms were exposed twice-daily to noncoherent blue and red light (LumaCare; 420 nm and 635 nm). The energy density applied was 72 J cm^-2 for blue light and 43.8 J cm², 87.6 J cm², and 175.5 J cm² for red light. Positive control (PC) and negative control (NC) groups were treated twice-daily for 1 min with 0.12% chlorhexidine (CHX) and 0.89% NaCl respectively. Biofilms were analyzed for colony forming units (CFU), dry-weight, and exopolysaccharides (EPS-soluble and EPS-insoluble). Data was analyzed by one-way ANOVA and Tukey post hoc test (α = 0.05). Dry-weight was lower than NC (p < 0.001) and approached PC levels with both red and blue light treatments. CFU were also lower in groups exposed to blue light and higher durations of red light (p < 0.05). EPS-soluble and EPS-insoluble measures were variably reduced by these light exposures. In conclusion, twice-daily exposure to both blue and red lights affect the biofilm development and physiology of polysaccharide production and are potential mechanisms for the control of C. albicans biofilm matrix development.

Fluconazole impacts the extracellular matrix of fluconazole-susceptible and -resistant Candida albicans and Candida glabrata biofilms

Background: Fluconazole (FLZ) is a drug commonly used for the treatment of Candida infections. However, β-glucans in the extracellular matrices (ECMs) hinder FLZ penetration into Candida biofilms, while extracellular DNA (eDNA) contributes to the biofilm architecture and resistance. Methods: This study characterized biofilms of FLZ-sensitive (S) and -resistant (R) Candida albicans and Candida glabrata in the presence or absence of FLZ focusing on the ECM traits. Biofilms of C. albicans American Type Culture Collection (ATCC) 90028 (CaS), C. albicans ATCC 96901 (CaR), C. glabrata ATCC 2001 (CgS), and C. glabrata ATCC 200918 (CgR) were grown in RPMI medium with or without FLZ at 5× the minimum inhibitory concentration (37°C/48 h). Biofilms were assessed by colony-forming unit (CFU)/mL, biomass, and ECM components (alkali-soluble polysaccharides [ASP], water-soluble polysaccharides [WSP], eDNA, and proteins). Scanning electron microscopy (SEM) was also performed. Data were analyzed by parametric and nonparametric tests (α  =  0.05). Results: In biofilms, FLZ reduced the CFU/mL of all strains (p < 0.001), except for CaS (p = 0.937). However, the ASP quantity in CaS was significantly reduced by FLZ (p = 0.034), while the drug had no effect on the ASP levels in other strains (p > 0.05). Total biomasses and WSP were significantly reduced by FLZ in the ECM of all yeasts (p < 0.001), but levels of eDNA and proteins were unaffected (p > 0.05). FLZ affected the cell morphology and biofilm structure by hindering hyphae formation in CaS and CaR biofilms, by decreasing the number of cells in CgS and CgR biofilms, and by yielding sparsely spaced cell agglomerates on the substrate. Conclusion: FLZ impacts biofilms of C. albicans and C. glabrata as evident by reduced biomass. This reduced biomass coincided with lowered cell numbers and quantity of WSPs. Hyphal production by C. albicans was also reduced.