Candida resistance and its clinical relevance

Consensus Gene Network Analysis Identifies the Key Similarities and Differences in Endothelial and Epithelial Cell Dynamics after Candida albicans Infection

Endothelial and epithelial cells are morphologically different and play a critical role in host defense during Candida albicans infection. Both cells respond to C. albicans infection by activating various signaling pathways and gene expression patterns. Their interactions with these pathogens can have beneficial and detrimental effects, and a better understanding of these interactions can help guide the development of new therapies for C. albicans infection. To identify the differences and similarities between human endothelial and oral epithelial cell transcriptomics during C. albicans infection, we performed consensus WGCNA on 32 RNA-seq samples by relating the consensus modules to endothelial-specific modules and analyzing the genes connected. This analysis resulted in the identification of 14 distinct modules. We demonstrated that the magenta module correlates significantly with C. albicans infection in each dataset. In addition, we found that the blue and cyan modules in the two datasets had opposite correlation coefficients with a C. albicans infection. However, the correlation coefficients and p-values between the two datasets were slightly different. Functional analyses of the hub of genes from endothelial cells elucidated the enrichment in TNF, AGE-RAGE, MAPK, and NF-κB signaling. On the other hand, glycolysis, pyruvate metabolism, amino acid, fructose, mannose, and vitamin B6 metabolism were enriched in epithelial cells. However, mitophagy, necroptosis, apoptotic processes, and hypoxia were enriched in both endothelial and epithelial cells. Protein-protein interaction analysis using STRING and CytoHubba revealed STAT3, SNRPE, BIRC2, and NFKB2 as endothelial hub genes, while RRS1, SURF6, HK2, and LDHA genes were identified in epithelial cells. Understanding these similarities and differences may provide new insights into the pathogenesis of C. albicans infections and the development of new therapeutic targets and interventional strategies.

Coexpression network analysis of human candida infection reveals key modules and hub genes responsible for host-pathogen interactions

Invasive fungal infections are a significant reason for morbidity and mortality among organ transplant recipients. Therefore, it is critical to investigate the host and candida niches to understand the epidemiology of fungal infections in transplantation. Candida albicans is an opportunistic fungal pathogen that causes fatal invasive mucosal infections, particularly in solid organ transplant patients. Therefore, identifying and characterizing these genes would play a vital role in understanding the complex regulation of host-pathogen interactions. Using 32 RNA-sequencing samples of human cells infected with C. albicans, we developed WGCNA coexpression networks and performed DESeq2 differential gene expression analysis to identify the genes that positively correlate with human candida infection. Using hierarchical clustering, we identified 5 distinct modules. We studied the inter- and intramodular gene network properties in the context of sample status traits and identified the highly enriched genes in the correlated modules. We identified 52 genes that were common in the most significant WGCNA turquoise module and differentially expressed genes in human endothelial cells (HUVEC) infection vs. control samples. As a validation step, we identified the differentially expressed genes from the independent Candida-infected human oral keratinocytes (OKF6) samples and validated 30 of the 52 common genes. We then performed the functional enrichment analysis using KEGG and GO. Finally, we performed protein-protein interaction (PPI) analysis using STRING and CytoHubba from 30 validated genes. We identified 8 hub genes (JUN, ATF3, VEGFA, SLC2A1, HK2, PTGS2, PFKFB3, and KLF6) that were enriched in response to hypoxia, angiogenesis, vasculogenesis, hypoxia-induced signaling, cancer, diabetes, and transplant-related disease pathways. The discovery of genes and functional pathways related to the immune system and gene coexpression and differential gene expression analyses may serve as novel diagnostic markers and potential therapeutic targets.

Biofilm and hyphal inhibitory synergistic effects of phytoactives piperine and cinnamaldehyde against Candida albicans

Oral candidiasis, the most common mycotic infection of the human oral cavity is non-life-threatening yet if untreated may advance as systemic infections. Ability of Candida albicans to adapt sessile lifestyle imparts resistance to drugs and host immunity. Consequently, due to limited effectiveness of conventional antifungal treatment, novel therapeutic strategies are required. In the present study, synergistic interaction of phytochemicals, piperine and cinnamaldehyde against the biofilm and hyphal of C. albicans was evaluated. Minimum inhibitory concentration (MIC) and biofilm inhibitory concentration (BIC) of piperine and cinnamaldehyde against C. albicans were analysed through microbroth dilution assay and crystal violet staining method, respectively. Combinatorial biofilm and hyphal inhibitory effect were investigated through checkerboard assay. In vitro results were validated through gene expression analysis. BIC of piperine and cinnamaldehyde was determined to be 32 µg/mL and 64 µg/mL, respectively. Interaction between these two phytocomponents was found to be synergistic and six different synergistic antibiofilm combinations were identified. Microscopic analysis of biofilm architecture also evidenced the biofilm and surface adherence inhibitory potential of piperine and cinnamaldehyde combinations. Phenotypic switching between yeast and hyphal morphological forms was influenced by synergistic combinations. qPCR analysis corroborated the results of in vitro activities. nrg1 and trp1, the negative transcriptional regulators of filamentous growth were upregulated whereas other genes that are involved in biofilm formation, filamentous growth, adhesion etc were found to be downregulated. These proficient phytochemical combinations provide a new therapeutic avenue for the treatment of biofilm associated oral candidiasis and to combat the recurrent infections due to antibiotic resistance.

Carvacrol Induces Candida albicans Apoptosis Associated With Ca2+/Calcineurin Pathway

As the prevalence of systemic fungal infections caused by Candida albicans gradually increases, it is necessary to explore potential and effective antifungals. Carvacrol is reported to be lethally toxic to C. albicans, involving several potential mechanisms. However, the form and specific mechanism of cell death caused by this compound has not been delineated. In this study, we found that carvacrol could significantly decrease C. albicans survival rates, consistent with previous researches. Further examination proved that carvacrol treatment caused cell membrane permeability and depolarization. To elucidate the association between cell death and apoptosis, DNA fragmentation and metacaspase activation were determined; as expected, these two apoptosis-related markers were clearly observed. Moreover, total and mitochondrial reactive oxygen species (ROS) levels were elevated, and both mitochondrial transmembrane potential and morphology were disrupted. Additionally, cytosolic and mitochondrial calcium levels were also increased by carvacrol. Calcineurin inhibition experiments revealed cyclosporine A (CsA) addition notably rescued cell growth and inhibited metacaspase activation, indicating that carvacrol triggered C. albicans apoptosis through inducing calcineurin activation. Carvacrol was demonstrated to both have low toxicity and be effective in alleviating systemic infections with C. albicans, which might be via its antifungal and immunomodulation activities. This study suggests that carvacrol has excellent potential as a natural protective compound against C. albicans infections.

Multicenter Evaluation of the Accelerate PhenoTest BC Kit for Rapid Identification and Phenotypic Antimicrobial Susceptibility Testing Using Morphokinetic Cellular Analysis

We describe results from a multicenter study evaluating the Accelerate Pheno system, a first of its kind diagnostic system that rapidly identifies common bloodstream pathogens from positive blood cultures within 90 min and determines bacterial phenotypic antimicrobial susceptibility testing (AST) results within ∼7 h. A combination of fresh clinical and seeded blood cultures were tested, and results from the Accelerate Pheno system were compared to Vitek 2 results for identification (ID) and broth microdilution or disk diffusion for AST. The Accelerate Pheno system accurately identified 14 common bacterial pathogens and two Candida spp. with sensitivities ranging from 94.6 to 100%. Of fresh positive blood cultures, 89% received a monomicrobial call with a positive predictive value of 97.3%. Six common Gram-positive cocci were evaluated for ID. Five were tested against eight antibiotics, two resistance phenotypes (methicillin-resistant Staphylococcus aureus and Staphylococcus spp. [MRSA/MRS]), and inducible clindamycin resistance (MLSb). From the 4,142 AST results, the overall essential agreement (EA) and categorical agreement (CA) were 97.6% and 97.9%, respectively. Overall very major error (VME), major error (ME), and minor error (mE) rates were 1.0%, 0.7%, and 1.3%, respectively. Eight species of Gram-negative rods were evaluated against 15 antibiotics. From the 6,331 AST results, overall EA and CA were 95.4% and 94.3%, respectively. Overall VME, ME, and mE rates were 0.5%, 0.9%, and 4.8%, respectively. The Accelerate Pheno system has the unique ability to identify and provide phenotypic MIC and categorical AST results in a few hours directly from positive blood culture bottles and support accurate antimicrobial adjustment.

A farnesoic acid-responsive transcription factor, Hot1, regulates yeast-hypha morphogenesis in Candida albicans

Candida albicans hyphal formation is inhibited by a quorum-sensing molecule, farnesoic acid, which accumulates in the medium as the cells proliferate. We recently showed that Pho81 is essential for the inhibition of hyphal growth by farnesoic acid. Here, we describe a newly identified regulator, Hot1, which increases the expression of PHO81. The binding site of Hot1 in the PHO81 promoter region was identified by DNase I protection assay. The hot1Δ mutant grows extensively as filaments. Furthermore, the inhibition of hyphal formation and the repression of major signaling pathway components in response to farnesoic acid are defective in hot1Δ mutant cells. These data suggest an important role for HOT1 in the inhibition of hyphal development by farnesoic acid in this fungus.

Endoplasmic reticulum-derived reactive oxygen species (ROS) is involved in toxicity of cell wall stress to Candida albicans

The cell wall is an important cell structure in both fungi and bacteria, and hence becomes a common antimicrobial target. The cell wall-perturbing agents disrupt synthesis and function of cell wall components, leading to cell wall stress and consequent cell death. However, little is known about the detailed mechanisms by which cell wall stress renders fungal cell death. In this study, we found that ROS scavengers drastically attenuated the antifungal effect of cell wall-perturbing agents to the model fungal pathogen Candida albicans, and these agents caused remarkable ROS accumulation and activation of oxidative stress response (OSR) in this fungus. Interestingly, cell wall stress did not cause mitochondrial dysfunction and elevation of mitochondrial superoxide levels. Furthermore, the iron chelator 2,2'-bipyridyl (BIP) and the hydroxyl radical scavengers could not attenuate cell wall stress-caused growth inhibition and ROS accumulation. However, cell wall stress up-regulated expression of unfold protein response (UPR) genes, enhanced protein secretion and promoted protein folding-related oxidation of Ero1, an important source of ROS production. These results indicated that oxidation of Ero1 in the endoplasmic reticulum (ER), rather than mitochondrial electron transport and Fenton reaction, contributed to cell wall stress-related ROS accumulation and consequent growth inhibition. Our findings uncover a novel link between cell wall integrity (CWI), ER function and ROS production in fungal cells, and shed novel light on development of strategies promoting the antifungal efficacy of cell wall-perturbing agents against fungal infections.

Resistance Surveillance in Candida albicans: A Five-Year Antifungal Susceptibility Evaluation in a Brazilian University Hospital

Candida albicans caused 44% of the overall candidemia episodes from 2006 to 2010 in our university tertiary care hospital. As different antifungal agents are used in therapy and also immunocompromised patients receive fluconazole prophylaxis in our institution, this study aimed to perform an antifungal susceptibility surveillance with the C.albicans bloodstream isolates and to characterize the fluconazole resistance in 2 non-blood C.albicans isolates by sequencing ERG11 gene. The study included 147 C. albicans bloodstream samples and 2 fluconazole resistant isolates: one from oral cavity (LIF 12560 fluconazole MIC: 8μg/mL) and one from esophageal cavity (LIF-E10 fluconazole MIC: 64μg/mL) of two different patients previously treated with oral fluconazole. The in vitro antifungal susceptibility to amphotericin B (AMB), 5-flucytosine (5FC), fluconazole (FLC), itraconazole (ITC), voriconazole (VRC), caspofungin (CASP) was performed by broth microdilution methodology recommended by the Clinical and Laboratory Standards Institute documents (M27-A3 and M27-S4, CLSI). All blood isolates were classified as susceptible according to CLSI guidelines for all evaluated antifungal agents (MIC range: 0,125–1.00 μg/mL for AMB, ≤0.125–1.00 μg/mL for 5FC, ≤0.125–0.5 μg/mL for FLC, ≤0.015–0.125 μg/mL for ITC, ≤0.015–0.06 μg/mL for VRC and ≤0.015–0.125 μg/mL for CASP). In this study, we also amplified and sequenced the ERG11 gene of LIF 12560 and LIF-E10 C.albicans isolates. Six mutations encoding distinct amino acid substitutions were found (E116D, T128K, E266D, A298V, G448V and G464S) and these mutations were previously described as associated with fluconazole resistance. Despite the large consumption of antifungals in our institution, resistant blood isolates were not found over the trial period. Further studies should be conducted, but it may be that the very prolonged direct contact with the oral antifungal agent administered to the patient from which was isolated LIF E-10, may have contributed to the development of resistance.

Structure-based designing of sordarin derivative as potential fungicide with pan-fungal activity

Fungal infections have become a significant problem for immunosuppressed patients. Sordarin, a promising fungicidal agent, inhibits fungal protein synthesis by impairing elongation factor-2 (eEF2) function. Intriguingly, despite high sequence similarity among eEF2s from different species, sordarin has been shown to inhibit translation specifically in certain fungi while unable to do so in some other fungal species (e.g. Candida parapsilosis and Candida lusitaniae). The sordarin binding site on eEF2 as well as its mechanism of action is known. In a previous study, we have detailed the interactions between sordarin and eEF2 cavities from different fungal species at the molecular level and predicted the probable cause of sordarin sensitivity. Guided by our previous analysis, we aimed for computer-aided designing of sordarin derivatives as potential fungicidal agents that still remain ineffective against human eEF2. We have performed structural knowledge-based designing of several sordarin derivatives and evaluated predicted interactions of those derivatives with the sordarin-binding cavities of different eEF2s, against which sordarin shows no inhibitory action. Our analyses identify an amino-pyrrole derivative as a good template for further designing of promising broad-spectrum antifungal agents. The drug likeness and ADMET prediction on this derivative also supports its suitability as a drug candidate.

Advanced Applications of RNA Sequencing and Challenges

Next-generation sequencing technologies have revolutionarily advanced sequence-based research with the advantages of high-throughput, high-sensitivity, and high-speed. RNA-seq is now being used widely for uncovering multiple facets of transcriptome to facilitate the biological applications. However, the large-scale data analyses associated with RNA-seq harbors challenges. In this study, we present a detailed overview of the applications of this technology and the challenges that need to be addressed, including data preprocessing, differential gene expression analysis, alternative splicing analysis, variants detection and allele-specific expression, pathway analysis, co-expression network analysis, and applications combining various experimental procedures beyond the achievements that have been made. Specifically, we discuss essential principles of computational methods that are required to meet the key challenges of the RNA-seq data analyses, development of various bioinformatics tools, challenges associated with the RNA-seq applications, and examples that represent the advances made so far in the characterization of the transcriptome.

New signaling pathways govern the host response to C. albicans infection in various niches

Candida albicans, the major invasive fungal pathogen of humans, can cause both debilitating mucosal infections and fatal invasive infections. Understanding the complex nature of the host-pathogen interaction in each of these contexts is essential to developing desperately needed therapies to treat fungal infections. RNA-seq enables a systems-level understanding of infection by facilitating comprehensive analysis of transcriptomes from multiple species (e.g., host and pathogen) simultaneously. We used RNA-seq to characterize the transcriptomes of both C. albicans and human endothelial cells or oral epithelial cells during in vitro infection. Network analysis of the differentially expressed genes identified the activation of several signaling pathways that have not previously been associated with the host response to fungal pathogens. Using an siRNA knockdown approach, we demonstrate that two of these pathways-platelet-derived growth factor BB (PDGF BB) and neural precursor-cell-expressed developmentally down-regulated protein 9 (NEDD9)-govern the host-pathogen interaction by regulating the uptake of C. albicans by host cells. Using RNA-seq analysis of a mouse model of hematogenously disseminated candidiasis (HDC) and episodes of vulvovaginal candidiasis (VVC) in humans, we found evidence that many of the same signaling pathways are activated during mucosal (VVC) and/or disseminated (HDC) infections in vivo. Our analyses have uncovered several signaling pathways at the interface between C. albicans and host cells in various contexts of infection, and suggest that PDGF BB and NEDD9 play important roles in this interaction. In addition, these data provide a valuable community resource for better understanding host-fungal pathogen interactions.

Antifungal activity of four honeys of different types from Algeria against pathogenic yeast: Candida albicans and Rhodotorula sp

OBJECTIVE

To evaluate the antifungal activity of four honeys of different types from Algeria against pathogenic yeast i.e. Candida albicans (C. albicans) and Rhodotorula sp.

METHODS

Four Algeria honeys of different botanical origin were analyzed to test antifungal effect against C. albicans, and Rhodotorula sp. Different concentrations (undiluted, 10%, 30%, 50% and 70% w/v) of honey were studied in vitro for their antifugal activity using C. albicans and Rhodotorula sp. as fungal strains.

RESULTS

The range of the diameter of zone of inhibition of various concentrations of tested honeys was (7-23 mm) for Rhodotorula sp., while C. albicans showed clearly resistance towards all concentrations used. The MICs of tested honey concentrations against C. albicans and Rhodotorula sp. were (70.09-93.48)% and (4.90-99.70)% v/v, respectively.

CONCLUSIONS

This study demonstrates that, in vitro, these natural products have clearly an antifungal activity against Rhodotorula sp. and C. albicans.

Novel mechanisms of surfactants against Candida albicans growth and morphogenesis

Candida albicans is a common opportunistic fungal pathogen, causing not only superficial mucosal infections but also life-threatening systemic candidiasis in immune-compromised individuals. Surfactants are a kind of amphiphilic compounds implemented in a wide range of applications. Although their antimicrobial activity has been characterized, their effect on C. albicans physiology remains to be elucidated. In this study, we investigated the inhibitory effect of two representative surfactants, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), on C. albicans growth and morphogenesis. Both surfactants exhibited inhibitory effect on C. albicans growth. This effect was not attributed to plasma membrane (PM) damage, but was associated with mitochondrial dysfunction. Excitingly, the surfactants, especially CTAB, showed strong inhibitory effect on hyphal development (IC50=0.183 ppm for CTAB and 6.312 ppm for SDS) and biofilms (0.888 ppm for CTAB and 76.092 ppm for SDS). Actin staining and Hwp1-GFP localization further revealed that this inhibition is related to abnormal organization of actin skeleton and subsequent defect in polarized transport of hyphae-related factors. This study sheds a novel light on the antimicrobial mechanisms of surfactants, and suggests these agents as potential drugs against C. albicans hyphae-related infections in clinical practice.

Role of TFP1 in vacuolar acidification, oxidative stress and filamentous development in Candida albicans

The vacuolar-type H(+)-ATPase (V-ATPase) is a multiprotein complex consisting of the V0 and V1 sectors, and is required for vacuolar acidification and virulence in the opportunistic fungal pathogen Candida albicans. In this study, we identified C. albicans Tfp1 as a putative subunit of V-ATPase, and explored its importance in multiple cellular processes. Our results revealed that Tfp1 played an essential role in vacuolar acidification and endocytic trafficking. In addition, the tfp1Δ/Δ mutant was sensitive to alkaline pH and elevated calcium concentrations, which is characteristic of loss of V-ATPase activity. The mutant also showed hypersensitivity to metal ions which might be attributed to a defect in sequestration of toxic ions to the vacuole through proton gradient produced by V-ATPase. Interestingly, deletion of TFP1 triggered endogenous oxidative stress even without exogenous oxidants. Compared with the wild-type strain, the tfp1Δ/Δ mutant showed significantly higher ROS levels and lower expression levels of redox-related genes with the addition of hydrogen peroxide (H2O2). Western blotting analysis showed that deletion of TFP1 significantly reduced the expression of Cap1 under H2O2 treatment, which contributes to the regulation of genes involved in the oxidative stress response. Furthermore, the tfp1Δ/Δ mutant showed significantly impaired filamentous development in hyphal induction media, and was avirulent in a mouse model of systemic candidiasis. Taken together, our results suggested that the putative V1 subunit Tfp1 is essential for vacuolar function and C. albicans pathogenesis, and provided a promising candidate for antifungal drugs.

Inhibitory effect of verapamil on Candida albicans hyphal development, adhesion and gastrointestinal colonization

Candida albicans morphogenesis and gastrointestinal colonization are closely associated with the pathogenicity of this pathogen. This study investigated the in vitro and in vivo effect of verapamil, a calcium channel blocker, on these processes. Exposure to ≥ 10 μg mL(-1) verapamil led to a significant decrease of C. albicans hyphal cells. The ability to adhere to a polystyrene surface and buccal epithelial cells was inhibited by exposure to ≥ 20 μg mL(-1) verapamil. Detection of the Hwp1-green fluorescent protein fusion protein showed that verapamil inhibited expression and transport of Hwp1, indicating its activity against both the regulation network of morphogenesis-associated proteins and the secretory pathway in C. albicans. Moreover, treatment with verapamil at 10 mg (kg day)(-1) led to a remarkable decrease in gastrointestinal-colonizing fungal cells. This study revealed the inhibitory effect of verapamil on C. albicans hyphal development, adhesion and gastrointestinal colonization, which is relevant to decreased expression and abnormal transport of the proteins required for morphogenesis. Therefore, verapamil may be taken into account when choosing an antifungal therapy against C. albicans colonization and infection.

UPC2 is universally essential for azole antifungal resistance in Candida albicans

In Candida albicans, the transcription factor Upc2 is central to the regulation of ergosterol biosynthesis. UPC2-activating mutations contribute to azole resistance, whereas disruption increases azole susceptibility. In the present study, we investigated the relationship of UPC2 to fluconazole susceptibility, particularly in azole-resistant strains. In addition to the reduced fluconazole MIC previously observed with UPC2 disruption, we observed a lower minimum fungicidal concentration (MFC) for a upc2Δ/Δ mutant than for its azole-susceptible parent, SC5314. Moreover, the upc2Δ/Δ mutant was unable to grow on a solid medium containing 10 μg/ml fluconazole and exhibited increased susceptibility and a clear zone of inhibition by Etest. Time-kill analysis showed higher fungistatic activity against the upc2Δ/Δ mutant than against SC5314. UPC2 disruption in strains carrying specific resistance mutations also resulted in reduced MICs and MFCs. UPC2 disruption in a highly azole resistant clinical isolate containing multiple resistance mechanisms likewise resulted in a reduced MIC and MFC. This mutant was unable to grow on a solid medium containing 10 μg/ml fluconazole and exhibited increased susceptibility and a clear zone of inhibition by Etest. Time-kill analysis showed increased fungistatic activity against the upc2Δ/Δ mutant in the resistant background. Microarray analysis showed attenuated induction by fluconazole of genes involved in sterol biosynthesis, iron transport, or iron homeostasis in the absence of UPC2. Taken together, these data demonstrate that the UPC2 transcriptional network is universally essential for azole resistance in C. albicans and represents an attractive target for enhancing azole antifungal activity.

Novel Macrocyclic Amidinoureas: Potent Non-Azole Antifungals Active against Wild-Type and Resistant Candida Species

Novel macrocyclic amidinourea derivatives 11, 18, and 25 were synthesized and evaluated as antifungal agents against wild-type and fluconazole resistant Candida species. Macrocyclic compounds 11 and 18 were synthesized through a convergent approach using as a key step a ring-closing metathesis macrocyclization reaction, whereas compounds 25 were obtained by our previously reported synthetic pathway. All the macrocyclic amidinoureas showed antifungal activity toward different Candida species higher or comparable to fluconazole and resulted highly active against fluconazole resistant Candida strains showing in many cases minimum inhibitory concentration values lower than voriconazole.

The P-type ATPase Spf1 is required for endoplasmic reticulum functions and cell wall integrity in Candida albicans

Endoplasmic reticulum (ER) is crucial for protein folding, glycosylation and secretion in eukaryotic organisms. These important functions are supported by high levels of Ca(2+) in the ER. We have recently identified a putative ER Ca(2+) pump in Candida albicans, called Spf1, which plays key roles in maintenance of cellular Ca(2+) homeostasis, morphogenesis and virulence. In this study, we purified Spf1 and confirmed that it is a P-type ATPase, suggesting its role in maintaining high levels of ER Ca(2+). Disruption of SPF1 caused severe defects in glycosylation of the ER-localized protein Cdc101 and secretory acid phosphatase, and a decrease in expression of SEC61 which encodes an important ER protein. Moreover, the spf1Δ/Δ mutant showed increased sensitivity to cell wall stresses, abnormal cell wall composition, delayed cell wall reconstruction and decreased flocculation and adherence, indicating its defect in cell wall integrity (CWI). We also revealed that disruption of SPF1 has an impact on gene expression related to CWI and morphogenesis. This study provides evidence that Spf1, as a P-type ATPase, is essential for ER functions and consequent CWI, implicating a role of ER Ca(2+) homeostasis in C. albicans physiology.

[Sexually transmitted infections of the oral cavity]

Various sexual practices like fellatio, cunnilingus, or anilingus (rimming) can cause both symptomatic and asymptomatic oral infections in both sexes. Clinically apparent lesions are found in primary, secondary, and tertiary syphilis, in acute HIV infection and the subsequent stage of immunodeficiency (opportunistic infections), as well as in herpes and human papilloma virus infections. Genital candidiasis also can be transmitted to the oral cavity. Depending on the infective agent transmitted, ulcerative, inflammatory or papillomatous lesions of the lips, tongue, mucous membranes and pharynx occur. Oropharyngeal infections with Neisseria gonorrhoeae or Chlamydia trachomatis (Serovar D-K) can cause pharyngitis and tonsillitis with sore throat, but are completely asymptomatic in most cases. Asymptomatic infections are an important, but frequently overlooked reservoir for new infections. Systemic treatment of oral STI's usually is the same as that for anogenital infections. It can be accompanied by symptomatic topical therapy. When the tonsils and other difficult to reach tissues are infected, higher doses and an antibiotic with good tissue penetration are recommended.

Identification of fungicidal 2,6-disubstituted quinolines with activity against Candida biofilms

We have identified two subseries of 2,6-disubstituted quinolines, consisting of 6-amide and 6-urea derivatives, which are characterized by fungicidal activity against Candida albicans with minimal fungicidal concentration (MFC) values < 15 µM. The 6-amide derivatives displayed the highest fungicidal activity against C. albicans, in particular compounds 1, 5 and 6 characterized by MFC values of 6.25–12.5 µM. Compounds 1 and 5 of this series displayed fungicidal activity against the emerging pathogen Candida glabrata(MFC < 50 µM). The 6-amide derivatives 1, 2, 5, and 6 and the 6-urea derivatives 10, 12, 13 and 15 could also eradicate C. albicans biofilms. We found that the 6-urea derivatives 10, 13, and 15 induced accumulation of endogenous reactive oxygen species in Candida albicans biofilms.

Comprehensive annotation of the transcriptome of the human fungal pathogen Candida albicans using RNA-seq

Candida albicans is the major invasive fungal pathogen of humans, causing diseases ranging from superficial mucosal infections to disseminated, systemic infections that are often lifethreatening. We have used massively parallel high-throughput sequencing of cDNA (RNA-seq) to generate a high-resolution map of the C. albicans transcriptome under several different environmental conditions. We have quantitatively determined all of the regions that are transcribed under these different conditions, and have identified 602 novel transcriptionally active regions (TARs) and numerous novel introns that are not represented in the current genome annotation. Interestingly, the expression of many of these TARs is regulated in a condition-specific manner. This comprehensive transcriptome analysis significantly enhances the current genome annotation of C. albicans, a necessary framework for a complete understanding of the molecular mechanisms of pathogenesis for this important eukaryotic pathogen.

In vitro activity of aminosterols against yeasts involved in blood stream infections

Squalamine and other aminosterols have demonstrated interesting antimicrobial activities against clinical bacterial isolates and a limited number of reference yeast strains. We aimed to test whether squalamine and a synthetic aminosterol derivative (ASD) display any in vitro activity comparable to currently available systemic antifungals, an acceptable safety index, as well as to provide insights into their mechanism of action. The minimum inhibitory concentrations (MICs) of squalamine, ASD and available antifungals were determined against 21 yeast isolates that were recovered from cases of fungemia. Remarkably, homogeneous MICs ranging from 8-16 mg/L and from 1-2 mg/L were noted for squalamine and ASD, respectively, as opposes the heterogeneous in vitro activity of available systemic antifungals. Aminosterols induced haemolysis, a surrogate for toxic effects to mammalian cells, at concentrations high above their MICs. In time-kill studies, killing was as fast with ASD as with amphotericin B. Both aminosterols induced a time-dependent disruption of yeast membrane, as evidenced by gradual increase of ATP efflux. In conclusion, our preliminary data indicate that aminosterols have the potential to be further developed as antifungals. Additional work is warranted to assess their toxicity and activity in experimental models.

Role of Candida albicans Aft2p transcription factor in ferric reductase activity, morphogenesis and virulence

The ability of Candida albicans to act as an opportunistic fungal pathogen is linked to its ability to switch among different morphological forms. This conversion is an important feature of C. albicans and is correlated with its pathogenesis. Many conserved positive and negative transcription factors regulate morphogenetic transition of C. albicans. Here, we show the results of functional analysis of CaAFT2, which is an orthologue of the Saccharomyces cerevisiae AFT2 gene. We have cloned CaAFT2 which has an ability to complement the S. cerevisiae aft1Δ mutant strain growth defect. Interestingly, although disruption of the AFT2 gene did not affect cell growth in solid and liquid iron-limited conditions, the cell surface ferric reductase activity was significantly decreased. Importantly, deletion of AFT2 in C. albicans led to growth of a smooth colony with no peripheral hyphae. Moreover, virulence of an aft2Δ/aft2Δ mutant was markedly attenuated in a mouse model. Our results suggest that CaAft2p represents a novel activator and that it functions in ferric reductase activity, morphogenesis and virulence in C. albicans.

In vitro activity of xanthorrhizol against Candida glabrata, C. guilliermondii, and C. parapsilosis biofilms

The formation of Candida biofilms has important clinical ramifications, because these biofilms exhibit increased resistance to conventional antifungal therapies. The aim of this study was to investigate the activity of xanthorrhizol on biofilms produced by non-C. albicans Candida (NCAC) species, including C. glabrata, C. guilliermondii, and C. parapsilosis. NCAC biofilms were generated in flat-bottom 96-well microtiter plates and quantified using the XTT (2, 3 - bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenyl amino) carbonyl]-2H-tetrazolium hydroxide) reduction assay. The NCAC biofilms at adherent, intermediate, and mature growth phases were treated with 0.5-512 μg/ml of xanthorrhizol for 24 h. The ranges of sessile minimum inhibitory concentrations (SMICs) of xanthorrhizol against C. glabrata, C. guilliermondii, and C. parapsilosis biofilms were 8-32 μg/ml, 8-16 μg/ml, and 8-64 μg/ml, respectively. Xanthorrhizol affected cell density that had an indirect effect on the biofilm OD(490). The compound eradicated the viable cells of the C. glabrata and C. parapsilosis biofilms at the adherent growth phase at 16 μg/ml and that of C. guilliermondii at 8 μg/ml. Treatment with 128 μg/ml of xanthorrhizol reduced the OD(490) of C. glabrata, C. guilliermondii, and C. parapsilosis biofilms at the mature growth phase by 77.8%, 88.5%, and 64.5%, respectively. These results indicate that xanthorrhizol exhibits potent activity against NCAC biofilms in vitro. Therefore, xanthorrhizol has potential therapeutic value in treating biofilm-associated NCAC infections and should be further evaluated in vivo.

Inter-kingdom encounters: recent advances in molecular bacterium-fungus interactions

Interactions between bacteria and fungi are well known, but it is often underestimated how intimate and decisive such associations can be with respect to behaviour and survival of each participating organism. In this article we review recent advances in molecular bacterium-fungus interactions, combining the data of different model systems. Emphasis is given to the positive or negative consequences these interactions have on the microbe accommodating plants and animals. Intricate mechanisms of antagonism and tolerance have emerged, being as important for the biological control of plants against fungal diseases as for the human body against fungal infections. Bacterial growth promoters of fungal mycelium have been characterized, and these may as well assist plant-fungus mutualism as disease development in animals. Some of the toxins that have been previously associated with fungi are actually produced by endobacteria, and the mechanisms that lie behind the maintenance of such exquisite endosymbioses are fascinating. Bacteria do cause diseases in fungi, and a synergistic action between bacterial toxins and extracellular enzymes is the hallmark of such diseases. The molecular study of bacterium-fungus associations has expanded our view on microbial communication, and this promising field shows now great potentials in medicinal, agricultural and biotechnological applications.

Bacterial peptidoglycan triggers Candida albicans hyphal growth by directly activating the adenylyl cyclase Cyr1p

Human serum potently induces hyphal development of the polymorphic fungal pathogen Candida albicans, a phenotype that contributes critically to infections. The fungal adenylyl cyclase Cyr1p is a key component of the cAMP/PKA-signaling pathway that controls diverse infection-related traits, including hyphal morphogenesis. However, identity of the serum hyphal inducer(s) and its fungal sensor remain unknown. Our initial analyses of active serum fractions revealed signs of bacterial peptidoglycan (PGN)-like molecules. Here, we show that several purified and synthetic muramyl dipeptides (MDPs), subunits of PGN, can strongly promote C. albicans hyphal growth. Analogous to PGN recognition by the mammalian sensors Nod1 and Nod2 through their leucine-rich-repeat (LRR) domain, we show that MDPs activate Cyr1p by directly binding to its LRR domain. Given the abundance of PGN in the intestine, a natural habitat and invasion site for C. albicans, our findings have important implications for the mechanisms of infection by this pathogen.

An Avenue to the Sordarin Core Adaptable to Analog Synthesis

We describe a synthesis of ketones 3 (X = O-R or CN; Y = H or alkyl), which are useful building blocks for the preparation of analogs of the potent antifungal agent sordarin, 1. Congeners of 1 constructed from 3 should permit detailed SAR investigations of the terpenoid core of the natural product.

Environmental sensing and signal transduction pathways regulating morphopathogenic determinants of Candida albicans

Candida albicans is an opportunistic fungal pathogen that is found in the normal gastrointestinal flora of most healthy humans. However, under certain environmental conditions, it can become a life-threatening pathogen. The shift from commensal organism to pathogen is often correlated with the capacity to undergo morphogenesis. Indeed, under certain conditions, including growth at ambient temperature, the presence of serum or N-acetylglucosamine, neutral pH, and nutrient starvation, C. albicans can undergo reversible transitions from the yeast form to the mycelial form. This morphological plasticity reflects the interplay of various signal transduction pathways, either stimulating or repressing hyphal formation. In this review, we provide an overview of the different sensing and signaling pathways involved in the morphogenesis and pathogenesis of C. albicans. Where appropriate, we compare the analogous pathways/genes in Saccharomyces cerevisiae in an attempt to highlight the evolution of the different components of the two organisms. The downstream components of these pathways, some of which may be interesting antifungal targets, are also discussed.

Galanin message-associated peptide suppresses growth and the budded-to-hyphal-form transition of Candida albicans

The expression of the mRNA encoding galanin message-associated peptide (GMAP) in human keratinocytes is upregulated by lipopolysaccharides and exposure to Candida albicans. GMAP has growth-inhibiting activity against C. albicans and inhibits the budded-to-hyphal-form transition, establishing GMAP as a possible new component of the innate immune system.

Chemical composition, toxicological aspects and antifungal activity of essential oil from Lippia sidoides Cham

OBJECTIVES

The aims of this study were to test the essential oil from Lippia sidoides Cham. for antifungal activity, in vitro, against Candida spp. and Microsporum canis, to evaluate its acute and subchronic toxicological effects, in vivo, and to determine its chemical constituents.

METHODS

The antifungal activity, in vitro, was initially evaluated by the agar-well diffusion technique, and the MIC and minimum fungicidal concentration (MFC) were determined by the broth microdilution method. The acute and subchronic toxicological effects were determined in mice and rats, respectively. The chemical composition of the essential oil was determined by gas chromatography coupled to mass spectroscopy.

RESULTS

The essential oil obtained from L. sidoides was effective against all tested strains by the agar-well diffusion method. The MICs of L. sidoides essential oil for strains of M. canis ranged from 4 to 70 mg/L and the MFCs ranged from 9 to 150 mg/L. The MICs for strains of Candida spp. ranged from 620 to 2500 mg/L and the MFCs ranged from 1250 to 5000 mg/L. The main constituents of L. sidoides essential oil were thymol (59.65%), E-caryophyllene (10.60%) and p-cymene (9.08%). The acute administration of the essential oil up to 3 g/kg by the oral route to mice was devoid of overt toxicity. The 30 day oral administration of L. sidoides oil (117.95 mg/kg/day) to rats did not induce any significant histopathological, haematological or serum biochemical alterations.

CONCLUSIONS

The essential oil from L. sidoides may be a promising source in the search for new antifungal drugs due to its efficacy and low toxicity.