Carbon substrates promotes stress resistance and drug tolerance in clinical isolates of Candida tropicalis

Candida tropicalis is a human pathogen and one of the most prevalent non-Candida albicans Candida (NCAC) species causing invasive infections. Azole antifungal resistance in C. tropicalis is also gradually increasing with the increasing incidence of infections. The pathogenic success of C. tropicalis depends on its effective response in the host microenvironment. To become a successful pathogen, cellular metabolism, and physiological status determine the ability of the pathogen to counter diverse stresses inside the host. However, to date, limited knowledge is available on the impact of carbon substrate metabolism on stress adaptation and azole resistance in C. tropicalis. In this study, we determined the impact of glucose, fructose, and sucrose as the sole carbon source on the fluconazole resistance and osmotic (NaCl), oxidative (H2O2) stress adaptation in C. tropicalis clinical isolates. We confirmed that the abundance of carbon substrates influences or increases drug resistance and osmotic and oxidative stress tolerance in C. tropicalis. Additionally, both azole-resistant and susceptible isolates showed similar stress adaptation phenotypes, confirming the equal efficiency of becoming successful pathogens irrespective of drug susceptibility profile. To the best of our knowledge, our study is the first on C. tropicalis to demonstrate the direct relation between carbon substrate metabolism and stress tolerance or drug resistance.

Inhibition of the morphological transition of Candida spp. by riparins I-IV

Candida spp. is an opportunistic pathogen capable of causing superficial to invasive infections. Morphological transition is one of the main virulence factors of this genus and, therefore, is an important variable to be considered in pharmacological interventions. Riparins I, II, III, and IV are alkamide-type alkaloids extracted from the unripe fruit of Aniba riparia, whose remarkable pharmacological properties were previously demonstrated. This work aimed to evaluate in silico and in vitro the inhibitory effects of Riparins on the morphological transition of Candida albicans, Candida tropicalis, and Candida krusei. Molecular docking was applied to analyze the inhibitory effects of riparins against proteins such as N-acetylglucosamine, CYP-51, and protein kinase A (PKA) using the Ramachandran plot. The ligands were prepared by MarvinSketch and Spartan software version 14.0, and MolDock Score and Rerank Score were used to analyze the affinity of the compounds. In vitro analyses were performed by culturing the strains in humid chambers in the presence of riparins or fluconazole (FCZ). The morphology was observed through optical microscopy, and the size of the hyphae was determined using the ToupView software. In silico analysis demonstrated that all riparins are likely to interact with the molecular targets: GlcNAc (>50%), PKA (>60%), and CYP-51 (>70%). Accordingly, in vitro analysis showed that these compounds significantly inhibited the morphological transition of all Candida strains. In conclusion, this study demonstrated that riparins inhibit Candida morphological transition and, therefore, can be used to overcome the pathogenicity of this genus.

Unravelling the temporal and spatial variation of fungal phylotypes from embryo to adult stages in Atlantic salmon

Early microbial colonization has a profound impact on host physiology during different stages of ontogeny. Although several studies have focused on early bacterial colonization and succession, the composition and role of fungal communities are poorly known in fish. Here, we sequenced the internal transcribed spacer 2 (ITS2) region of fungi to profile the mycobiome associated with the eggs, hatchlings and intestine of Atlantic salmon at various freshwater and marine stages. In most of the stages studied, fungal diversity was lower than bacterial diversity. There were several stage-specific fungal phylotypes belonging to different stages of ontogeny but some groups, such as Candida tropicalis, Saccharomyces cerevisiae, Alternaria metachromatica, Davidiella tassiana and Humicola nigrescens, persisted during successive stages of ontogeny. We observed significant changes in the intestinal fungal communities during the first feeding. Prior to first feeding, Humicola nigrescens dominated, but Saccharomyces cerevisiae (10 weeks post hatch) and Candida tropicalis (12 weeks post hatch) became dominant subsequently. Seawater transfer resulted in a decrease in alpha diversity and an increase in Candida tropicalis abundance. We also observed notable variations in beta diversity and composition between the different farms. Overall, the present study sheds light on the fungal communities of Atlantic salmon from early ontogeny to adulthood. These novel findings will also be useful in future studies investigating host-microbiota interactions in the context of developing better nutritional and health management strategies for Atlantic salmon farming.

Rapid Inactivation of mixed biofilms of Candida albicans and Candida tropicalis using antibacterial photodynamic therapy: Based on PAD™ Plus

Background

To investigate the sterilizing effect of antimicrobial photodynamic therapy (aPDT) based on PAD™ Plus on mixed biofilms of Candida albicans and Candida tropicalis.

Methods

A mature mixed biofilm model of C. albicans and C. tropicalis was constructed in vitro. FITC-concanavalin A staining was conducted to observe the formation of the extracellular matrix. MTT assay was performed to determine biofilm viability. The chromogenic medium was used to examine the Candida composition of the mixed biofilms. For aPDT treatment, based on PAD™ Plus, the biofilms were incubated with 1 mg/mL TBO for 1, 5, or 10 min, followed by 500 or 750 mW LED illumination for 1 or 2 min. The live/dead fungi were detected by SYTO9/propidium iodide staining. A multivariate factorial design was conducted to analyze the correlations of parameters with the inactivation effect of the mixed biofilms.

Results

Mature mixed biofilms formed at 24 h after seeding. Compared with untreated biofilms, following 1-min TBO incubation, 500 mW LED illumination for 1 min inactivated more than 90% of the fungi. Extending the incubation time did not significantly improve the inactivation effect. Application of 750 mW output power or 2 min LED illumination inactivated more than 99% of the fungi without increasing other parameters.

Conclusions

PAD™ Plus combined with 1 mg/mL TBO can rapidly inactivate the mature mixed biofilms of C. albicans and C. tropicalis, serving as a robust platform for the treatment of mixed infections of C. albicans and C. tropicalis.

Similarities and Differences among Species Closely Related to Candida albicans: C. tropicalis, C. dubliniensis, and C. auris

Although Candida species are widespread commensals of the microflora of healthy individuals, they are also among the most important human fungal pathogens that under certain conditions can cause diseases (candidiases) of varying severity ranging from mild superficial infections of the mucous membranes to life-threatening systemic infections. So far, the vast majority of research aimed at understanding the molecular basis of pathogenesis has been focused on the most common species—Candida albicans. Meanwhile, other closely related species belonging to the CTG clade, namely, Candida tropicalis and Candida dubliniensis, are becoming more important in clinical practice, as well as a relatively newly identified species, Candida auris. Despite the close relationship of these microorganisms, it seems that in the course of evolution, they have developed distinct biochemical, metabolic, and physiological adaptations, which they use to fit to commensal niches and achieve full virulence. Therefore, in this review, we describe the current knowledge on C. tropicalis, C. dubliniensis, and C. auris virulence factors, the formation of a mixed species biofilm and mutual communication, the environmental stress response and related changes in fungal cell metabolism, and the effect of pathogens on host defense response and susceptibility to antifungal agents used, highlighting differences with respect to C. albicans. Special attention is paid to common diagnostic problems resulting from similarities between these species and the emergence of drug resistance mechanisms. Understanding the different strategies to achieve virulence, used by important opportunistic pathogens of the genus Candida, is essential for proper diagnosis and treatment.

Profuse diversity and acidogenicity of the candida-biome of deep carious lesions of Severe Early Childhood Caries (S-ECC)

Introduction: The retentive niches of deep caries lesions have a distinct biome. Methods: We evaluated the site-specific (occlusal and proximal) Candida-biome of Severe-Early Childhood Caries (S-ECC) in 66- children (132 lesions). Asymptomatic primary molars fitting the definition of the International Caries Detection and Assessment-(ICDAS)-caries-code 5/6 were analyzed. Deep-dentinal sampling and simultaneous assessment of pH were performed. Clinical isolates were speciated using multiplex-PCR and evaluated for their acidogenic and aciduric potential.Results: Surprisingly, a high prevalence of Candida species (72.7%), either singly or in combination, was noted from both the proximal and occlusal cavities. C. tropicalis was the most prevalent species (47%; 34/72), followed by C. krusei (43.1%; 31/72) and C. albicans (40.3%; 29/72), with C. glabrata being the least (9.7%; 7/72). Over 45% low-pH niches (pH <7) of both sites yielded either dual or triple species of Candida. Genotyping revealed three distinct C. albicans genotypes (A, B, and C) with (14/29; 48.3%) of strains belonging to Genotype A. All four evaluated Candida species exhibited acidogenic and aciduric potential, C. tropicalis being the most potent.Conclusion: This, the first report of the high-density, multispecies, yeast colonization of deep-dentinal lesions in S-ECC, suggests that the Candida-biome plays a significant etiologic role in the condition, possibly due to their profound acidogenicity in milieus rich in dietary carbohydrates.

The Anti-Biofilm Efficacy of Caffeic Acid Phenethyl Ester (CAPE) In Vitro and a Murine Model of Oral Candidiasis

Candida albicans is the main fungal species associated with the development of oral candidiasis. Currently, therapeutic options for these infections are limited by the adverse effects of antifungal drugs and by the emergence of drug resistant strains. Thus, the development of new antifungal agents is needed for the prevention and treatment of oral Candida infections. Caffeic acid phenethyl ester (CAPE) is a natural compound from propolis polyphenolic groups that exhibits many pharmacological properties. In this study, we investigated whether CAPE can have antifungal and immunomodulatory effects on oral candidiasis. Preliminary tests to assess the antifungal activity of CAPE were performed using the Minimum Inhibitory Concentration (MIC) assay that demonstrated inhibition in a range from 16 to 32 μg/mL, confirming its antifungal activity on several C. albicans strains isolated from the oral cavity. Subsequently, we analyzed Candida spp biofilms formed in vitro, in which CAPE treatment at 5 x MIC caused a reduction of 68.5% in the total biomass and ~2.60 Log in the viable cell count (CFU/mL) in relation to the untreated biofilm (p<0.0001). Next, RNA was extracted from untreated and CAPE-treated biofilms and analyzed by real-time qPCR. A series of genes analyzed (ALS1, ECE1, EPA1, HWP1, YWP1, BCR1, BGR1, CPH1, EFG1, NDT80, ROB1, TEC1, UME6, SAP2, SAP5, PBL2, and LIP9) were downregulated by CAPE compared to the untreated control group (p<0.0001). In in vivo studies using Galleria mellonella, the treatment with CAPE prolonged survival of larvae infected by C. albicans by 44.5% (p < 0.05) and accompanied by a 2.07-fold increase in the number of hemocytes. Flow cytometry revealed the most prominent increases were in types P2 and P3 hemocytes, granular cells, which phagocytize pathogens. In addition, CAPE treatment decreased the fungal load in the hemolymph and stimulated the expression of antifungal peptide genes such as galiomicin and gallerimycin. The antifungal and immunomodulatory activities observed in G. mellonella were extended to a murine model of oral candidiasis, in which CAPE decreased the levels of C. albicans colonization (~2 log CFU/mL) in relation to the untreated control group. In addition, CAPE treatment significantly reduced pseudomembranous lesions, invasion of hyphae on epithelium surfaces, tissue damage and inflammatory infiltrate (p < 0.05). CAPE was also able to increase the expression of β-defensin 3 compared to the infected and untreated group by 3.91-fold (p < 0.0001). Taken together, these results show that CAPE has both antifungal and immunomodulatory effects, making it a promising natural antifungal agent for the treatment and prevention of candidiasis and shows impact to oral candidiasis.

Antimicrobial photodynamic therapy for oral Candida infection in adult AIDS patients: A pilot clinical trial

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) using methylene blue (MB) plus potassium iodide (KI) has been shown to be effective in killing Candida albicans in many in vitro and in vivo studies, however, there are limited reports of clinical investigations. This study aimed to explore the clinical application of aPDT with MB plus KI for the treatment of oral infection caused by C. albicans in adult acquired immune deficiency syndrome (AIDS) patients.

METHODS

A total of 21 adult AIDS patients with C. albicans oral candidiasis were divided into two groups according to MB concentration and received two consecutive aPDT treatments. Immediately before and after the aPDT treatments, C. albicans yeast isolates were recovered to measure the colony-forming units per mL (CFU/mL), biofilm formation, and to analyze the 25S rDNA genotype. Patients were assessed for the clinical recovery of oral lesions and improvement of symptoms.

RESULTS

The Log₁₀ CFU/mL of C. albicans decreased significantly after the second aPDT but not the first aPDT. There was no significant difference between the two MB concentrations. Both aPDT protocols decreased the oral lesions and clinical symptoms with no significant difference after 2-fraction aPDT. The biofilm formation of C. albicans isolates did not change before and after aPDT. The killing efficiency of 2-fraction-aPDT was not associated with either biofilm formation or 25S rDNA genotype.

CONCLUSIONS

Two-fraction-aPDT with MB plus KI could reduce the number of viable C. albicans fungal cells and improve the clinical symptoms of oral candidiasis in adult AIDS patients, regardless of the biofilm formation or 25S rDNA genotype of infected C. albicans isolates.

Identification of Fungi Isolated from Oral Cavity of Patients with HIV Using MALDI-TOF MS

BACKGROUND

A growing incidence of invasive fungal infections, especially among immunocompromised patients, has given increased significance to microbiological diagnostics of yeast-like fungi. More accurate and faster fungi identification methods that can compete with classical methods are being searched for. In this paper, classical microbiological methods are compared to MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry).

METHODS

The diagnostic material was collected from buccal mucosa from 98 adults, including 69 with HIV. Only positive cultures were included in the study.

RESULTS

Matching results were obtained in 45 samples, and there were nonmatching results in 35 samples, with the majority of these in the study group, constituting 50% of identifications within this group. A particularly common mistake resulting from the use of classical methods is the false identification of C. dubliniensis as C. albicans. Additionally, C. tropicalis proves to be difficult to identify.

CONCLUSIONS

Our results and literature data suggest that MALDI-TOF MS should be considered an effective alternative to classical methods in terms of fungi identification, especially among HIV-positive patients, due to the different morphology of fungal colonies.

N-acetylglucosamine-mediated morphological transition in Candida albicans and Candida tropicalis

Morphological transitions in Candida species are key factors in facilitating invasion and adapting to environmental changes. N-acetylglucosamine (GlcNAc) is a monosaccharide signalling molecule that can regulate morphological transitions in Candida albicans and Candida tropicalis. Interestingly, although the uptake and metabolic pathways of GlcNAc and GlcNAc-mediated white-to-opaque cell switching are similar between the two Candida species, GlcNAc induces hyphal development in C. albicans, whereas it suppresses hyphal development in C. tropicalis. These findings indicate that the characteristics of C. albicans and C. tropicalis in response to GlcNAc are remarkably different. Here, we compare the conserved and divergent GlcNAc-mediated signalling pathways and catabolism between the two Candida species. Deletion of NGT1, a GlcNAc transportation gene, inhibited hyphal formation in C. albicans but promoted hyphal development in C. tropicalis. To further understand these opposite effects on filamentous growth in response to GlcNAc in the two Candida species, the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signalling pathways in both C. albicans and C. tropicalis were compared. Interestingly, GlcNAc activated the cAMP/PKA signalling pathway of the two Candida species, suggesting that the hyphal development-regulated circuit is remarkably diverse between the two species. Indeed, the Ndt80-like gene REP1, which is critical for regulating GlcNAc catabolism, exhibits distinct roles in the hyphal development of C. albicans and C. tropicalis. These data suggest possible reasons for the divergent hyphal growth response in C. albicans and C. tropicalis upon GlcNAc induction.

Candida Pathogenicity and Interplay with the Immune System

Candida species are opportunistic fungal pathogens that are part of the normal skin and mucosal microflora. Overgrowth of Candida can cause infections such as thrush or life-threatening invasive candidiasis in immunocompromised patients. Though Candida albicans is highly prevalent, several non-albicans species are also isolated from nosocomial infections. Candida sp. are over presented in the gut of people with Crohn's disease and certain types of neurological disorders, with hyphal form and biofilms being the most virulent states. In addition, Candida uses several secreted and cell surface molecules such as pH related antigen 1, High affinity glucose transporter, Phosphoglycerate mutase 1 and lipases to establish pathogenicity. A strong innate immune response is elicited against Candida via dendritic cells, neutrophils and macrophages. All three complement pathways are also activated. Production of proinflammatory cytokines IL-10 and IL-12 signal differentiation of CD4⁺ cells into Th1 and Th2 cells, whereas IL-6, IL-17 and IL-23 induce Th17 cells. Importance of T-lymphocytes is reflected in depleted T-cell count patients being more prone to Candidiasis. Anti- Candida antibodies also play a role against candidiasis using various mechanisms such as targeting virulent enzymes and exhibiting direct candidacidal activity. However, the significance of antibody response during infection remains controversial. Furthermore, some of the Candida strains have evolved molecular strategies to evade the sophisticated host attack by proteolysis of components of immune system and interfering with immune signalling pathways. Emergence of several non-albicans species that are resistant to current antifungal agents makes treatment more difficult. Therefore, deeper insight into interactions between Candida and the host immune system is required for discovery of novel therapeutic options.

Dynamics of Mono- and Dual-Species Biofilm Formation and Interactions Between Paracoccidioides brasiliensis and Candida albicans

The oral cavity is a highly diverse microbial environment in which microorganisms interact with each other, growing as biofilms on biotic and abiotic surfaces. Understanding the interaction among oral microbiota counterparts is pivotal for clarifying the pathogenesis of oral diseases. Candida spp. is one of the most abundant fungi in the oral mycobiome with the ability to cause severe soft tissue lesions under certain conditions. Paracoccidioides spp., the causative agent of paracoccidioidomycosis, may also colonize the oral cavity leading to soft tissue damage. It was hypothesized that both fungi can interact with each other, increasing the growth of the biofilm and its virulence, which in turn can lead to a more aggressive infectivity. Therefore, this study aimed to evaluate the dynamics of mono- and dual-species biofilm growth of Paracoccidioides brasiliensis and Candida albicans and their infectivity using the Galleria mellonella model. Biomass and fungi metabolic activity were determined by the crystal violet and the tetrazolium salt reduction tests (XTT), respectively, and the colony-forming unit (CFU) was obtained by plating. Biofilm structure was characterized by both scanning electronic- and confocal laser scanning- microscopy techniques. Survival analysis of G. mellonella was evaluated to assess infectivity. Our results showed that dual-species biofilm with P. brasiliensis plus C. albicans presented a higher biomass, higher metabolic activity and CFU than their mono-species biofilms. Furthermore, G. mellonella larvae infected with P. brasiliensis plus C. albicans presented a decrease in the survival rate compared to those infected with P. brasiliensis or C. albicans, mainly in the form of biofilms. Our data indicate that P. brasiliensis and C. albicans co-existence is likely to occur on oral mucosal biofilms, as per in vitro and in vivo analysis. These data further widen the knowledge associated with the dynamics of fungal biofilm growth that can potentially lead to the discovery of new therapeutic strategies for these infections.

Antimicrobial peptide CGA-N12 decreases the Candida tropicalis mitochondrial membrane potential via mitochondrial permeability transition pore

Amino acid sequence from 65th to 76th residue of the N-terminus of Chromogranin A (CGA-N12) is an antimicrobial peptide (AMP). Our previous studies showed that CGA-N12 reduces Candida tropicalis mitochondrial membrane potential. Here, we explored the mechanism that CGA-N12 collapsed the mitochondrial membrane potential by investigations of its action on the mitochondrial permeability transition pore (mPTP) complex of C. tropicalis. The results showed that CGA-N12 induced cytochrome c (Cyt c) leakage, mitochondria swelling and led to polyethylene glycol (PEG) of molecular weight 1000 Da penetrate mitochondria. mPTP opening inhibitors bongkrekic acid (BA) could contract the mitochondrial swelling induced by CGA-N12, but cyclosporin A (CsA) could not. Therefore, we speculated that CGA-N12 could induce C. tropicolis mPTP opening by preventing the matrix-facing (m) conformation of adenine nucleotide transporter (ANT), thereby increasing the permeability of the mitochondrial membrane and resulted in the mitochondrial potential dissipation.

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.

Genetic diversity of Candida albicans isolates recovered from hospital environments and patients with severe acquired brain injuries

Although the epidemiology of pathogenic Candida species causing invasive human diseases is changing, Candida albicans still remains the most common cause of bloodstream infections worldwide. The propensity of this pathogen to cause infections is undoubtedly the result of its unique genetic plasticity that allow it to adapt and respond quickly to a myriad of changing conditions both in the host and in the environment. For this reason, we decided to investigate the genetic diversity of this important fungal pathogen in a particular category of patients with severe neurological deficits including the hospital environments where they are hospitalized. Genetic diversity of 21 C. albicans isolates recovered from blood, hands of healthcare workers and hospital environments was evaluated by using multilocus sequence typing (MLST) which revealed a high genetic heterogeneity with a set of 18 diploid sequence types (DSTs) recovered among 21 isolates investigated. Interestingly, 13 of these 18 MLST genotypes were completely new and added to the C. albicans MLST central database. Six eBURST clonal complexes (CC-1, CC-2, CC-6, CC-9, CC-27 and CC-42) and three singletons contained all DSTs found in this study. Among all the new DSTs identified, DST3388 was the most intriguing as this genotype was recovered from a typical C. albicans isolate clustering within the MLST-Clade 13, the most divergent evolutionary lineage within C. albicans population containing only isolates with unusual phenotypes originally known as Candida africana. In conclusion, the results of this study expand our understanding of the molecular epidemiology and global population structure of C. albicans suggesting that further studies on different categories of patients and hospital environments are needed to better understand how the population of this species adapts and evolves in heterogeneous hosts and changing environments.

Filamentous Non-albicans Candida Species Adhere to Candida albicans and Benefit From Dual Biofilm Growth

Non-albicans Candida species (NACS) are often isolated along with Candida albicans in cases of oropharyngeal candidiasis. C. albicans readily forms biofilms in conjunction with other oral microbiota including both bacteria and yeast. Adhesion between species is important to the establishment of these mixed biofilms, but interactions between C. albicans and many NACS are not well-characterized. We adapted a real-time flow biofilm model to study adhesion interactions and biofilm establishment in C. albicans and NACS in mono- and co-culture. Out of five NACS studied, only the filamenting species C. tropicalis and C. dubliniensis were capable of adhesion with C. albicans, while C. parapsilosis, C. lusitaniae, and C. krusei were not. Over the early phase (0-4 h) of biofilm development, both mono- and co-culture followed similar kinetics of attachment and detachment events, indicating that initial biofilm formation is not influenced by inter-species interactions. However, the NACS showed a preference for inter-species cell-cell interactions with C. albicans, and at later time points (5-11 h) we found that dual-species interactions impacted biofilm surface coverage. Dual-species biofilms of C. tropicalis and C. albicans grew more slowly than C. albicans alone, but achieved higher surface coverage than C. tropicalis alone. Biofilms of C. dubliniensis with C. albicans increased surface coverage more rapidly than either species alone. We conclude that dual culture biofilm of C. albicans with C. tropicalis or C. dubliniensis offers a growth advantage for both NACS. Furthermore, the growth and maintenance, but not initial establishment, of dual-species biofilms is likely facilitated by interspecies cell-cell adherence.

Influence of Streptococcus mitis and Streptococcus sanguinis on virulence of Candida albicans: in vitro and in vivo studies

The aim was to evaluate in vitro possible interactions, gene expression, and biofilm formation in species of Candida albicans, Streptococcus mitis, and Streptococcus sanguinis and their in vivo pathogenicity. The in vitro analysis evaluated the effects of S. mitis and S. sanguinis on C. albicans's biofilm formation by CFU count, filamentation capacity, and adhesion (ALS1, ALS3, HWP1) and transcriptional regulatory gene (BCR1, CPH1, EFG1) expression. In vivo studies evaluated the pathogenicity of the interaction of the microorganisms on Galleria mellonella, with analyses of the CFU per milliliter count and filamentation. In vitro results indicated that there was an observed decrease in CFU (79.4-71.5%) in multi-species biofilms. The interaction with S. mitis inhibited filamentation, which seems to increase its virulence factor with over-expression of genes ALS1, ALS3, and HWP1 as well the interaction with S. sanguinis as ALS3 and HWP1. S. mitis upregulated BRC1, CPH1, and EFG1. The histological images of in vivo study indicate an increase in the filamentation of C. albicans when in interaction with the other species. It was concluded that S. mitis interaction suggests increased virulence factors of C. albicans, with periods of lower virulence and proto-cooperation in the interaction with S. sanguinis.

Conserved and Divergent Functions of the cAMP/PKA Signaling Pathway in Candida albicans and Candida tropicalis

Fungal species undergo many morphological transitions to adapt to changing environments, an important quality especially in fungal pathogens. For decades, Candida albicans has been one of the most prevalent human fungal pathogens, and recently, the prevalence of Candida tropicalis as a causative agent of candidiasis has increased. In C. albicans, the ability to switch between yeast and hyphal forms is thought to be a key virulence factor and is regulated by multiple signaling cascades—including the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA), calcineurin, high-osmolarity glycerol (HOG), and mitogen-activated protein kinases (MAPK) signaling pathways—upon receiving environmental cues. The cAMP/PKA signaling pathway also triggers white-opaque switching in C. albicans. However, studies on C. tropicalis morphogenesis are limited. In this minireview, we discuss the regulation of the yeast-hypha transition, virulence, and white-opaque switching through the cAMP/PKA pathway in the closely related species C. albicans and C. tropicalis.