Molecular epidemiology, phylogeny and evolution of Candida albicans. Infect Genet Evol. 2014;21:166-178. [PMID: 24269341 DOI: 10.1016/j.meegid.2013.11.008]

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.

Evaluation of mixed biofilm production by Candida spp. and Staphylococcus aureus strains co-isolated from cystic fibrosis patients in northwest Algeria

Cystic fibrosis patients' lungs are chronically colonized by multiple microbial species capable of forming biofilms. This study aimed to characterize the polymicrobial biofilm formed by Candida spp. and S. aureus, co-isolated from sputum samples of cystic fibrosis patients regarding microbial density, metabolic activity, and structure. 67 samples from 28 patients were collected with a 96% alteration rate. 34% showed alterations by both Candida spp. and Gram-positive bacteria, predominantly Candida spp. and S. aureus in 77% of cases, accounting for 6 associations. Biofilm biomass was quantified using the crystal violet assay, and metabolic activity was assessed using the MTT reduction assay. Scanning electron microscopy analyzed the C. tropicalis/S. aureus24 biofilm architecture. Candida spp. isolates demonstrated the ability to form mixed biofilms with S. aureus. The C. tropicalis/S. aureus24 association exhibited the highest production of biofilm and metabolic activity, along with the C. albicans17/C. rugosa/S. aureus7 in both single and mixed biofilms.

A gain-of-function mutation in zinc cluster transcription factor Rob1 drives Candida albicans adaptive growth in the cystic fibrosis lung environment

Candida albicans chronically colonizes the respiratory tract of patients with Cystic Fibrosis (CF). It competes with CF-associated pathogens (e.g. Pseudomonas aeruginosa) and contributes to disease severity. We hypothesize that C. albicans undergoes specific adaptation mechanisms that explain its persistence in the CF lung environment. To identify the underlying genetic and phenotypic determinants, we serially recovered 146 C. albicans clinical isolates over a period of 30 months from the sputum of 25 antifungal-naive CF patients. Multilocus sequence typing analyses revealed that most patients were individually colonized with genetically close strains, facilitating comparative analyses between serial isolates. We strikingly observed differential ability to filament and form monospecies and dual-species biofilms with P. aeruginosa among 18 serial isolates sharing the same diploid sequence type, recovered within one year from a pediatric patient. Whole genome sequencing revealed that their genomes were highly heterozygous and similar to each other, displaying a highly clonal subpopulation structure. Data mining identified 34 non-synonymous heterozygous SNPs in 19 open reading frames differentiating the hyperfilamentous and strong biofilm-former strains from the remaining isolates. Among these, we detected a glycine-to-glutamate substitution at position 299 (G299E) in the deduced amino acid sequence of the zinc cluster transcription factor ROB1 (ROB1G299E), encoding a major regulator of filamentous growth and biofilm formation. Introduction of the G299E heterozygous mutation in a co-isolated weak biofilm-former CF strain was sufficient to confer hyperfilamentous growth, increased expression of hyphal-specific genes, increased monospecies biofilm formation and increased survival in dual-species biofilms formed with P. aeruginosa, indicating that ROB1G299E is a gain-of-function mutation. Disruption of ROB1 in a hyperfilamentous isolate carrying the ROB1G299E allele abolished hyperfilamentation and biofilm formation. Our study links a single heterozygous mutation to the ability of C. albicans to better survive during the interaction with other CF-associated microbes and illuminates how adaptive traits emerge in microbial pathogens to persistently colonize and/or infect the CF-patient airways.

Molecular epidemiology and antimicrobial resistance of vaginal Candida glabrata isolates in Namibia

Candida glabrata is the most common non-albicans Candida species that causes vulvovaginal candidiasis (VVC). Given the intrinsically low susceptibility of C. glabrata to azole drugs, investigations into C. glabrata prevalence, fungal susceptibility profile, and molecular epidemiology are necessary to optimise the treatment of VVC. This molecular epidemiological study was conducted to determine antifungal drug profile, single nucleotide polymorphisms (SNPs) associated with phenotypic antifungal resistance and epidemic diversity of C. glabrata isolates from women with VVC in Namibia. Candida glabrata isolates were identified using phenotypic and molecular methods. Antifungal susceptibility of strains was determined for fluconazole, itraconazole, amphotericin B, and anidulafungin. Whole genome sequencing was used to determine SNPs in antifungal resistance genes and sequence type (ST) allocation. Among C. glabrata isolates, all (20/20; 100%) exhibited phenotypic resistance to the azole class antifungal drug, (fluconazole), and phenotypic susceptibility to the polyene class (amphotericin B), and the echinocandins (anidulafungin). Non-synonymous SNPs were identified in antifungal resistance genes of all fluconazole-resistant C. glabrata isolates including ERG6 (15%), ERG7 (15%), CgCDR1 (25%), CgPDR1 (60%), SNQ2 (10%), FKS1 (5.0%), FKS2 (5.0%), CgFPS1 (5.0%), and MSH2 (15%). ST15 (n = 8/20, 40%) was predominant. This study provides important insight into phenotypic and genotypic antifungal resistance across C. glabrata isolates from women with VVC in Namibia. In this study, azole resistance is determined by an extensive range of SNPs, while the observed polyene and echinocandin resistance-associated SNPs despite phenotypic susceptibility require further investigation.

Multilocus sequence typing of Candida albicans oral isolates reveals high genetic relatedness of mother-child dyads in early life

Candida albicans is a pathogenic fungus recently recognized for its role in severe early childhood caries development (S-ECC). C. albicans oral colonization begins at birth, but the extent of the mother's involvement in yeast transmission to their children is unclear, therefore, this study used a prospective mother-infant cohort to investigate the maternal contribution of C. albicans oral colonization in early life. Oral samples were collected from 160 mother-child dyads during pregnancy and from birth to two years of life. We used whole-genome sequencing to obtain the genetic information of C. albicans isolates and examined the genetic relatedness of C. albicans between mothers and their children using Multilocus Sequence Typing. Multivariate statistical methods were used to identify factors associated with C. albicans' acquisition (horizontal and vertical transmissions). Overall, 227 C. albicans oral isolates were obtained from 93 (58.1%) of mother-child pairs. eBURST analysis revealed 16 clonal complexes, and UPGMA analysis identified 6 clades, with clade 1 being the most populated 124 isolates (54.6%). Significantly, 94% of mothers and children with oral C. albicans had highly genetically related strains, highlighting a strong maternal influence on children's C. albicans acquisition. Although factors such as race, ethnicity, delivery method, and feeding behaviors did not show a significant association with C. albicans vertical transmission, the mother's oral hygiene status reflected by plaque index (PI) emerged as a significant factor; Mothers with higher dental plaque accumulation (PI >=2) had a significantly increased risk of vertically transmitting C. albicans to their infants [odds ratio (95% confidence interval) of 8.02 (1.21, 53.24), p=0.03]. Furthermore, Black infants and those who attended daycare had an elevated risk of acquiring C. albicans through horizontal transmission (p <0.01). These findings highlight the substantial role of maternal transmission in the oral acquisition of C. albicans during early life. Incorporating screening for maternal fungal oral carriage and implementing oral health education programs during the perinatal stage may prove valuable in preventing fungal transmission in early infancy.

A reappraisal on amyloid cascade hypothesis: the role of chronic infection in Alzheimer's disease

Alzheimer disease (AD) is a progressive neurological disorder that accounted for the most common cause of dementia in the elderly population. Lately, 'infection hypothesis' has been proposed where the infection of microbes can lead to the pathogenesis of AD. Among different types of microbes, human immunodeficiency virus-1 (HIV-1), herpes simplex virus-1 (HSV-1), Chlamydia pneumonia, Spirochetes and Candida albicans are frequently detected in the brain of AD patients. Amyloid-beta protein has demonstrated to exhibit antimicrobial properties upon encountering these pathogens. It can bind to microglial cells and astrocytes to activate immune response and neuroinflammation. Nevertheless, HIV-1 and HSV-1 can develop into latency whereas Chlamydia pneumonia, Spirochetes and Candida albicans can cause chronic infections. At this stage, the DNA of microbes remains undetectable yet active. This can act as the prolonged pathogenic stimulus that over-triggers the expression of Aβ-related genes, which subsequently lead to overproduction and deposition of Aβ plaque. This review will highlight the pathogenesis of each of the stated microbial infection, their association in AD pathogenesis as well as the effect of chronic infection in AD progression. Potential therapies for AD by modulating the microbiome have also been suggested. This review will aid in understanding the infectious manifestations of AD.

Molecular fingerprinting by multi-locus sequence typing identifies microevolution and nosocomial transmission of Candida glabrata in Kuwait

Backgrounds

Candida glabrata is a frequently isolated non-albicans Candida species and invasive C. glabrata infections in older patients are associated with high mortality rates. Opportunistic Candida infections in critically ill patients may be either endogenous or nosocomial in origin and this distinction is critical for effective intervention strategies. This study performed multi-locus sequence typing (MLST) to study genotypic relatedness among clinical C. glabrata isolates in Kuwait.

Methods

Candida glabrata isolates (n = 91) cultured from 91 patients were analyzed by MLST. Repeat isolates (n = 16) from 9 patients were also used. Antifungal susceptibility testing for fluconazole, voriconazole, caspofungin and amphotericin B (AMB) was determined by Etest. Genetic relatedness was determined by constructing phylogenetic tree and minimum spanning tree by using BioNumerics software.

Results

Resistance to fluconazole, voriconazole and AMB was detected in 7, 2 and 10 C. glabrata isolates, respectively. MLST identified 28 sequence types (STs), including 12 new STs. ST46 (n = 33), ST3 (n = 8), ST7 (n = 6) and ST55 (n = 6) were prevalent in ≥4 hospitals. Repeat isolates obtained from same or different site yielded identical ST. No association of ST46 with source of isolation or resistance to antifungals was apparent. Microevolution and cross-transmission of infection was indicated in two hospitals that yielded majority (57 of 91, 67%) of C. glabrata.

Conclusion

Our data suggest that C. glabrata undergoes microevolution in hospital environment and can be nosocomially transmitted to other susceptible patients. Thus, proper infection control practices during routine procedures on C. glabrata-infected patients may prevent transmission of this pathogen to other hospitalized patients.

The effect of herbal medicine in innate immunity to Candida albicans

Candida albicans (C. albicans) is an opportunistic pathogenic fungus that often causes mucosal and systemic infections. Several pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs) and C-type lectin receptors (CLRs), have been implicated in the host recognition of C. albicans. These PRRs recognize the pathogen-associated molecular patterns (PAMPs) of C. albicans to activate innate immune cells, thereby rapidly inducing various inflammatory responses by activating intracellular signaling cascades. Herbal medicine and its active components deserve priority development due to their low toxicity and high antibacterial, antiviral and antifungal activities. This review discussed the activities of herbal compounds against C. albicans and their related mechanisms, especially their regulatory role on innate immune cells such as neutrophils, macrophages, and dendritic cells (DCs) implicated in C. albicans infections. Our work aims to find new therapeutic drugs and targets to prevent and treat diseases caused by C. albicans infection with the mechanisms by which this fungus interacts with the innate immune response.

Emergence of Antifungal Resistant Subclades in the Global Predominant Phylogenetic Population of Candida albicans

Candida albicans remains the most common species causing invasive candidiasis. In this study, we present the population structure of 551 global C. albicans strains. Of these, the antifungal susceptibilities of 370 strains were tested. Specifically, 66.6% of the azole-nonsusceptible (NS)/non-wild-type (NWT) strains that were tested belonged to Clade 1. A phylogenetic analysis, a principal components analysis, the population structure, and a loss of heterozygosity events revealed two nested subclades in Clade 1, namely, Clade 1-R and Clade 1-R-α, that exhibited higher azole-NS/NWT rates (75.0% and 100%, respectively). In contrast, 6.4% (21/326) of the non-Clade 1-R isolates were NS/NWT to at least 1 of 4 azoles. Notably, all of the Clade 1-R-α isolates were pan-azole-NS/NWT that carried unique A114S and Y257H double substitutions in Erg11p and had the overexpression of ABC-type efflux pumps introduced by the substitution A736V in transcript factor Tac1p. It is worth noting that the Clade 1-R and Clade 1-R-α isolates were from different cities that are distributed over a large geographic span. Our study demonstrated the presence of specific phylogenetic subclades that are associated with antifungal resistance among C. albicans Clade 1, which calls for public attention on the monitoring of the future spread of these clones. IMPORTANCE Invasive candidiasis is the most common human fungal disease among hospitalized patients, and Candida albicans is the predominant pathogen. Considering the large number of infected cases and the limited alternative therapies, the azole-resistance of C. albicans brings a huge clinical threat. Here, our study suggested that antifungal resistance in C. albicans could also be associated with phylogenetic lineages. Specifically, it was revealed that more than half of the azole-resistant C. albicans strains belonged to the same clade. Furthermore, two nested subclades of the clade exhibited extremely high azole-resistance. It is worth noting that the isolates of two subclades were from different cities that are distributed over a large geographic span in China. This indicates that the azole-resistant C. albicans subclades may develop into serious public health concerns.

Comprehensive whole genome sequencing with hybrid assembly of multi-drug resistant Candida albicans isolate causing cerebral abscess

Comprehensive whole genome sequencing (WGS) with hybrid assembly of a multi-drug resistant (MDR) Candida albicans (CA) isolate causing cerebral abscess was performed using Illumina paired end and Oxford Nanopore long read technologies. The innovative technologies utilized here enabled us to resolve fragmented assemblies, and implement comprehensive and detailed genomic analyses involved in antifungal resistance of Candida spp. Functionally important genes (MDR1, CDR2 and SQN2) involved in antifungal resistance were identified and a phylogenetic analysis of the clinical isolate was performed. Additionally, our clinical isolate was found to share 4 single nucleotide polymorphisms with two other sequenced strains of MDR C. auris (381 and 386) including translation elongation factor EF1α and EF3, ATPase activity associated proteins, and the lysine tRNA ligase.

Molecular characterization of fungal endophthalmitis and keratitis caused by yeasts

Candida species are the most common causes of sight-threatening fungal ocular infections in temperate regions of the world. Despite their relevance, little is known about the emergence of novel species and the molecular epidemiology of these infections. Here, we molecularly characterized 38 yeast isolates collected from patients diagnosed with endophthalmitis or keratitis at Massachusetts Eye and Ear from 2014 to 2021. Sequencing of the ITS1-5.8S-/ITS2 regions demonstrated that this population of yeasts was dominated by Candida spp. (37 out of 38; 97%), with 58% of the cases caused by C. albicans (n = 22) and the remaining by emerging non-albicans species, predominantly by C. parapsilosis (n = 8) and C. dubliniensis (n = 6). One isolate each was identified as C. tropicalis and Clavispora lusitaniae. Interestingly, all C. dubliniensis were isolated from endophthalmitis and most C. parapsilosis from keratitis. Multilocus sequence typing analysis of C. albicans showed a prevalence of CC-1 isolates that has DST69 as the putative founder, with 64% of them belonging to this clonal complex (CC). Isolates grouped within this cluster were more predominant in endophthalmitis (10 out of 14; 71%). One C. albicans CC-1 isolate was multi-azole resistant. In conclusion, we observed that nearly half of the ocular infections caused by yeasts are associated with C. albicans, with evidence for the emergence of non-albicans species that are differentially enriched in distinct ocular niches. Candida albicans isolates clustered within the predominant CC-1 group were particularly more common in endophthalmitis, demonstrating a potential pattern of ocular disease enrichment within this clade.

Role of Candida albicans in Oral Carcinogenesis

Oral carcinogenesis is also dependent on the balance of the oral microbiota. Candida albicans is a member oral microbiota that acts as an opportunistic pathogen along with changes in the epithelium that can predispose to premalignancy and/or malignancy. This systematic review uses the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines to analyze the role of Candida albicans in the process of oral carcinogenesis. Eleven articles qualified inclusion criteria, matched keywords, and provided adequate information about the carcinogenesis parameters of Candida albicans in oral cancer. Candida albicans in oral carcinogenesis can be seen as significant virulent factors for patients with oral squamous cell carcinoma (OSCC) or potentially malignant disorder (OPMD) with normal adjacent mucosa. Candida albicans have a role in the process of oral carcinogenesis concerning morphological phenotype changes in cell structure and genotype and contribute to the formation of carcinogenic substances that can affect cell development towards malignancy.

Genotyping of Candida albicans and Comparison of its Antifungal Resistance Pattern in the South Indian Region

Recent studies have documented an increase in the incidence of antifungal resistance in newly emerging species closely related to C. albicans, and the coexistence of genotypic variants. Hence, an application of PCR-based molecular typing is crucial in identifying these fungi. Our study used molecular methods to characterize the latest genotypic subgroups of C. albicans and analysed if there was a relationship between the genotypes and the antifungal resistance pattern. The study was conducted in JSS Hospital, Mysuru, Karnataka between July 2018 and December 2020. A total of 1427 Candida species were isolated from clinical samples. Candida albicans were isolated and confirmed using Germ tube test, ID VITEK 2 and PCR (ITS primer). DNA extraction was done using the Hi-Media Yeast DNA Extraction Kit. The amplified products were analysed using Agarose gel electrophoresis (2%). Among 1427 Candida species, 282 were Candida albicans. The following resistance was exhibited to major antifungals – Caspofungin (3.5%), Amphotericin B (1.4%), flucytosine (2.8%) Fluconazole (6%) Micafungin (2.8%) Voriconazole (3.1%) and all were sensitive to miconazole. ABC genotyping showed Genotype A (450 bp) predominant (87.58%) followed by genotype B (840bp) (9.92 %) and genotype C (450bp and 840 bp) (0.2%). Genotype D and E were not observed. Our study showed the growing antifungal resistance in clinical isolates. Genotype A was predominant in South Karnataka region followed by Genotype B and C. There was no correlation between genotyping and antifungal resistance. However, a study with greater number of samples from diverse geographical locations may give more insight.

Molecular cloning and functional characterization of UBC13 and MMS2 from Candida albicans

To maintain genome stability, eukaryotes have evolved a powerful DNA damage response system called DNA-damage tolerance (DDT) to deal with replication-blocking lesions. In the budding yeast Saccharomyces cerevisiae, K63-linked polyubiquitination of proliferating cell nuclear antigen (PCNA) is mediated by a Ubc13-Mms2 heterodimer, leading to error-free DDT. Candida albicans is one of the most studied fungal pathogens and to date no data regarding K63-linked ubiquitination or error-free DDT has been available. Here we report the identification and functional characterization of UBC13 and MMS2 genes from C. albicans. Both genes are highly conserved between S. cerevisiae and C. albicans. However, CaUbc13 differs from all other eukaryotes in that it contains a 21-amino acid tail that appears to attenuate its interaction with CaMms2, suggesting a possible regulatory mechanism in C. albicans. Both CaUBC13 and CaMMS2 genes can functionally rescue the corresponding budding yeast mutants from increased spontaneous mutagenesis and killing by DNA-damaging agents, indicating an error-free DDT pathway in C. albicans. Indeed Caubc13Δ/Δ and Camms2Δ/Δ null mutants were constructed and displayed characteristic sensitivity to DNA-damaging agents.

Prevalence of biofilms in Candida spp. bloodstream infections: A meta-analysis

CONTEXT

Candida-related infections are nowadays a serious Public Health Problem emerging multidrug-resistant strains. Candida biofilm also leads bloodstream infections to invasive systemic infections.

OBJECTIVE

The present meta-analysis aimed to analyze Candida biofilm rate, type, and antifungal resistance among hospitalized patients between 1995 and 2020.

DATA SOURCES

Web of Science, Scopus, PubMed, and Google Scholar databases were searched for English papers using the following medical subject heading terms (MESH): "invasive candidiasis"; "bloodstream infections"; "biofilm formation"; "biofilm-related infections"; "mortality"; and "prevalence".

STUDY SELECTION

The major inclusion criteria included reporting the rate of biofilm formation and the prevalence of biofilm-related to Candida species, including observational studies (more exactly, cohort, retrospective, and case-control studies). Furthermore, data regarding the mortality rate, the geographical location of the study set, and the use of anti-fungal agents in clinical isolates were also extracted from the studies.

DATA EXTRACTION

Independent extraction of articles by 2 authors using predefined data fields, including study quality indicators.

DATA SYNTHESIS

A total of 31 studies from publicly available databases met our inclusion criteria. The biofilm formation in the data set varied greatly from 16 to 100% in blood samples. Most of the studies belonged to Europe (17/31) and Asia (9/31). Forest plot showed a pooled rate of biofilm formation of 80.0% (CI: 67-90), with high heterogeneity (Q = 2567.45, I2 = 98.83, τ2 = 0.150) in random effects model (p < 0.001). The funnel plot and Egger's linear regression test failed to find publication bias (p = 0.896). The mortality rate in Candida-related bloodstream infections was 37.9% of which 70.0% were from biofilm-associated infections. Furthermore, Candida isolates were also characterized in low, intermediate, or high biofilm formers through their level of biofilm mass (crystal violet staining or XTT assays) after a 24h growth. When comparing between countries, statistical differences were obtained (p = 0.0074), showing the lower and higher biofilm prevalence values in Italy and Spain, respectively. The prevalence of low, intermediate, and high biofilms were 36.2, 18.9, and 35.0% (p < 0.0001), respectively. C. tropicalis was the prevalent species in high biofilm formation (67.5%) showing statistically significant differences when compared to other Candida species, except for C. krusei and C. glabrata. Finally, the rates of antifungal resistance to fluconazole, voriconazole, and caspofungin related to biofilm were 70.5, 67.9 and 72.8% (p < 0.001), respectively.

CONCLUSIONS

Early detection of biofilms and a better characterization of Candida spp. bloodstream infections should be considered, which eventually will help preserve public health resources and ultimately diminish mortality among patients.

GNP2 Encodes a High-Specificity Proline Permease in Candida albicans

The tight association of Candida albicans with the human host has driven the evolution of mechanisms that permit metabolic flexibility. Amino acids, present in a free or peptide-bound form, are abundant carbon and nitrogen sources in many host niches. In C. albicans, the capacity to utilize certain amino acids, like proline, is directly connected to fungal morphogenesis and virulence. Yet the precise nature of proline sensing and uptake in this pathogenic fungus has not been investigated. Since C. albicans encodes 10 putative orthologs of the four Saccharomyces cerevisiae proline transporters, we tested deletion strains of the respective genes and identified Gnp2 (CR_09920W) as the main C. albicans proline permease. In addition, we found that this specialization of Gnp2 was reflected in its transcriptional regulation and further assigned distinct substrate specificities for the other orthologs, indicating functional differences of the C. albicans amino acid permeases compared to the model yeast. The physiological relevance of proline uptake is exemplified by the findings that strains lacking GNP2 were unable to filament in response to extracellular proline and had a reduced capacity to damage macrophages and impaired survival following phagocytosis. Furthermore, GNP2 deletion rendered the cells more sensitive to oxidative stress, illustrating new connections between amino acid uptake and stress adaptation in C. albicans. IMPORTANCE The utilization of various nutrients is of paramount importance for the ability of Candida albicans to successfully colonize and infect diverse host niches. In this context, amino acids are of special interest due to their ubiquitous availability, relevance for fungal growth, and direct influence on virulence traits like filamentation. In this study, we identify a specialized proline transporter in C. albicans encoded by GNP2. The corresponding amino acid permease is essential for proline-induced filamentation, oxidative stress resistance, and fungal survival following interaction with macrophages. Altogether, this work highlights the importance of amino acid uptake for metabolic and stress adaptation in this fungus.

Wild Boar (Sus scrofa) as Reservoir of Zoonotic Yeasts: Bioindicator of Environmental Quality

Wildlife animals are recognized as reservoirs for zoonotic fungi and their faeces might play an important role in introducing pathogens into the environment. Thought wild boar (Sus scrofa) population has dramatically increased across Europe, information about their possible role in dissemination of zoonotic pathogenic yeasts in the environment is scant. Therefore, fecal samples (n = 124) from wild boars from Campania region (Southern Italy) were collected and yeasts identified biochemically and molecularly by sequencing of the internal transcribed spacer region and their phylogenetical relationship assessed. The antifungal susceptibility profiles of yeasts were also investigated using AFST-EUCAST method. Yeasts were isolated from 50.1% of the samples with the highest occurrence in samples from the province of Salerno (61.1%). A total of 368 Candida strains belonging to nine species were identified, with Candida albicans (45.7%), followed by Candida krusei (15.2%), Kazachstania slooffiae (9.8%) and Candida parapsilosis (7.6%) as the most prevalent identified species. Among C. albicans four sequence types (i.e., ST1-ST4) were identified with an intraspecific nucleotide difference up to 0.21%. The ML tree grouped all representative sequence types as paraphyletic clades with those of the references yeast species, respectively and supported by high bootstrap values. Fluconazole was the less active drug whereas, posaconazole, voriconazole, and isavuconazole the most active one. No resistance phenomena were observed for C. albicans and high MICs values for 5FC, azoles and echinocandines were registered in non-albicans Candida spp. This study showed, for the first time, the important role of wild boars in dissemination of pathogenic fungi in the environment. The absence of resistance phenomena in the Candida spp. might reflect environmental free from residues of azoles antifungals pollution or chemicals and suggests the role of wild boar as bio indicators of environment quality.

Parasexuality of Candida Species

While most fungi have the ability to reproduce sexually, multiple independent lineages have lost meiosis and developed parasexual cycles in its place. Emergence of parasexual cycles is particularly prominent in medically relevant fungi from the CUG paraphyletic group of Candida species. Since the discovery of parasex in C. albicans roughly two decades ago, it has served as the model for Candida species. Importantly, parasex in C. albicans retains hallmarks of meiosis including genetic recombination and chromosome segregation, making it a potential driver of genetic diversity. Furthermore, key meiotic genes play similar roles in C. albicans parasex and highlights parallels between these processes. Yet, the evolutionary role of parasex in Candida adaptation and the extent of resulting genotypic and phenotypic diversity remain as key knowledge gaps in this facultative reproductive program. Here, we present our current understanding of parasex, the mechanisms governing its regulation, and its relevance to Candida biology.

Fluorescent toys 'n' tools lighting the way in fungal research

Although largely overlooked compared to bacterial infections, fungal infections pose a significant threat to the health of humans and other organisms. Many pathogenic fungi, especially Candida species, are extremely versatile and flexible in adapting to various host niches and stressful situations. This leads to high pathogenicity and increasing resistance to existing drugs. Due to the high level of conservation between fungi and mammalian cells, it is hard to find fungus-specific drug targets for novel therapy development. In this respect, it is vital to understand how these fungi function on a molecular, cellular as well as organismal level. Fluorescence imaging allows for detailed analysis of molecular mechanisms, cellular structures and interactions on different levels. In this manuscript, we provide researchers with an elaborate and contemporary overview of fluorescence techniques that can be used to study fungal pathogens. We focus on the available fluorescent labelling techniques and guide our readers through the different relevant applications of fluorescent imaging, from subcellular events to multispecies interactions and diagnostics. As well as cautioning researchers for potential challenges and obstacles, we offer hands-on tips and tricks for efficient experimentation and share our expert-view on future developments and possible improvements.

Tyrosine-Templated Dual-Component Silver Nanomaterials Exhibit Photoluminescence and Versatile Antimicrobial Properties through ROS Generation

The role of small molecules in the preparation of metal nanomaterials generates considerable interest in the fields from materials science to interdisciplinary sciences. In this study, a small amino acid, l-tyrosine (Tyr), has been used as a ligand precursor for the preparation of silver nanomaterials (AgNMs) comprising a dual system: smaller silver nanoclusters (responsible exclusively for the photophysical properties) and larger silver nanoparticles (responsible exclusively for the antimicrobial properties). The luminescent properties of this AgNM system substantiate the role played by Tyr as a capping and a reducing agent outside the protein environment. An interesting feature of this report is the promising antimicrobial properties of the AgNMs against Saccharomyces cerevisiae, Candida albicans, Escherichia coli, and Bacillus cereus cell lines. The importance of this work is that this investigation demonstrates the combating ability of our AgNM system against pathogenic strains (C. albicans and B. cereus) as well. Moreover, the mechanistic aspects of the antimicrobial activity of the AgNMs were elucidated using various methods, such as propidium iodide staining, monitoring reactive oxygen species generation, leakage of proteins, DNA cleavage, etc. We propose that AgNM-mediated cytotoxicity in S. cerevisiae stems from the generation of singlet oxygen (¹O₂) species that create oxidative stress, disrupting the cell membrane and thereby resulting in leakage of proteins from the cells. This study can pave the way toward elucidating the role of a small molecule, Tyr, in the formation of NMs and describes the use of new NMs in potential antimicrobial applications.

Antifungal Drug Susceptibility and Genetic Characterization of Fungi Recovered from COVID-19 Patients

Fungal infections are common complications of respiratory viral infections and are associated with the increased need for intensive care and elevated mortality. Data regarding microbiological and molecular characteristics of such infections in COVID-19 patients are scarce. Here, we performed a comprehensive analysis, including species identification, antifungal susceptibility testing, molecular resistance determinants analysis, typing, and retrospective clinical data review, of fungal isolates recovered from 19 COVID-19 patients, who were hospitalized at the Hackensack University Medical Center (HUMC) in Hackensack, New Jersey, USA, in the initial phase of the pandemic from April–May 2020. In total, 17 Candida albicans, two C. parapsilosis, and two Aspergillus fumigatus were analyzed. All Candida spp. isolates were susceptible to micafungin and azole drugs (fluconazole, voriconazole, posaconazole, itraconazole, isavuconazole). A. fumigatus isolates were susceptible to micafungin and all triazole drugs except fluconazole (intrinsic resistance). Multilocus sequence typing (MLST) of C. albicans isolates revealed 15 different sequence types (STs), which clustered below the clade-defining limit of p-distance < 0.04. Pulsed-field gel electrophoresis (PFGE) karyotyping revealed no chromosomal rearrangements in these isolates. A. fumigatus isolates were of different, non-related genotypes. We speculate that virus- and drug-induced immunosuppression (94.7% of the patients received corticosteroids), together with prolonged hospital stay (median duration of 29 days) and mechanical ventilation (median duration of 24 days) likely increased the susceptibility to secondary respiratory and bloodstream infections in the studied patient population. The presence of fungi in blood or respiratory tract fluid was a prognosticator for poor clinical outcome, which presented as an 89.5% 30-day mortality in our patient cohort.

The combined application of the anti-RAS1 and anti-RIM101 2'-OMethylRNA oligomers enhances Candida albicans filamentation control

Whereas antisense oligomers (ASOs) have been successfully utilized to control gene expression, they have been little exploited to control Candida albicans virulence's determinants. Filamentation is an important virulence factor of C. albicans, and RAS1 and RIM101 genes are involved in its regulation. Thus, the main goal of this work was to project ASOs, based on 2'-OMethyl chemical modification, to target RAS1 and RIM101 mRNA and to validate its application either alone or in combination, to reduce Candida filamentation in different human body fluids.It was verified that both, anti-RAS1 2'OMe and anti-RIM101 2'OMe oligomers, were able to reduce the levels of RAS1 and RIM101 genes' expression and to significantly reduce C. albicans filamentation. Furthermore, the combined application of anti-RAS1 2'OMe oligomer and anti-RIM101 2'OMe oligomer enhances the control of C. albicans filamentation in artificial saliva and urine.Our work confirms that ASOs are useful tools for research and therapeutic development on the control of candidiasis.

LAY ABSTRACT

This work aimed to project antisense oligomers to control Candida albicans filamentation. The results revealed that the projected oligomers, anti-RAS1 2'OMe and anti-RIM101 2'OMe, were able to control RAS1 and RIM101 gene expression and to significantly reduce C. albicans filamentation.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

A Second-Generation Fungerp Analog, SCY-247, Shows Potent In Vivo Activity in a Murine Model of Hematogenously Disseminated Candida albicans

Echinocandins are a first-line therapy for Candida infections through their ability to inhibit the synthesis of polymer β-(1,3)-d-glucan. However, there has been an emergence of multidrug-resistant fungal species necessitating the development of novel antifungal agents to combat invasive fungal infections. SCY-247, a second-generation glucan synthase inhibitor of the triterpenoid class (fungerps), is currently being developed as a potential therapy option. We determined the pharmacokinetics (PKs) of SCY-247 following oral (gavage) administration in mice and evaluated the efficacy of SCY-247 in a murine model of hematogenously disseminated candidiasis caused by Candida albicans Plasma concentrations of SCY-247 were measurable through the last collected time point in all dose groups. Mean concentrations of SCY-247 increased with dose levels, with concentrations of SCY-247 higher after multiple doses than after a single dose. Treatment with SCY-247 resulted in decreased fungal burden and improvement in survival rates against C. albicans disseminated infection. Treatment with 10 mg/kg of body weight of SCY-247 showed a significant reduction in CFU compared with the untreated control (3-log decrease on average) (P = 0.008). Similarly, 40 mg/kg SCY-247 demonstrated a statistically significant reduction in kidney CFU compared with untreated mice (average log CFU ± SD of 2.38 ± 2.58 versus 6.26 ± 0.51; P = 0.001). Mice treated with SCY-247 at 40 mg/kg exhibited a 100% survival rate at the end of the study, contrasted with 62.5% (5 of 8) survival rate in untreated mice. The results of this investigation indicate that SCY-247 is a promising novel anti-fungal agent with activity against Candida infections.

Isolation, identification and genotyping of Candida albicans from Landes geese

In May 2018, Landes geese raised in Weifang, Shandong Province, China, developed a disease characterized by thickened oesophageal mucosa and white, round ulcers. Based on pathogen isolation and identification, differential culture and morphological observations, Candida albicans (C. albicans) was identified as the causative pathogen from the oesophagus of infected geese, and artificial infection experiments were then performed using the isolated strains. In experimental reproduction, the symptoms of infected geese were consistent with those of natural infection, and gosling morbidity and mortality were 75% and 60%, respectively. Re-isolation of the strain from the dead goslings confirmed C. albicans as the causative pathogen of oesophageal ulcers. We further performed internal transcribed space rDNA sequence analysis, ABC genotyping and multi-locus sequence typing analysis. We observed 100% sequence similarity between the two strains, designated as WFCL and WFLQ, which were isolated from different regions, with 100% homology between the strains isolated in the present study and the human-origin C. albicans strains isolated previously from China. The goose-origin strains isolated in this study and the human-origin C. albicans isolates were included in the same branch in phylogenetic trees analysis, indicating that the strain responsible for oesophageal ulcer in geese is closely related to human-origin C. albicans. In addition, based on eBURST analysis of sequence types, goose-origin C. albicans strains were relatively independent in terms of population evolution. To the best of our knowledge, this is the first detailed report on goose oesophageal ulceration caused by C. albicans infection in geese. Considering that C. albicans is an important zoonotic pathogen, this study provides a reference for further studies on avian C. albicans infections and is important for ensuring public health and safety.

Robust, Comprehensive Molecular, and Phenotypical Characterisation of Atypical Candida albicans Clinical Isolates From Bogotá, Colombia

Candida albicans is commensal in human microbiota and is known to be the commonest opportunistic pathogen, having variable clinical outcomes that can lead to up to 60% mortality. Such wide clinical behaviour can be attributed to its phenotypical plasticity and high genetic diversity. This study characterised 10 Colombian clinical isolates which had already been identified as C. albicans by molecular tests; however, previous bioinformatics analysis of protein mass spectra and phenotypical characteristics has shown that this group of isolates has atypical behaviour, sharing characteristics of both C. africana and C. albicans. This study was aimed at evaluating atypical isolates' pathogenic capability in the Galleria mellonella model; susceptibility profiles were determined and MLST was used for molecular characterisation. Cluster analysis, enabling unbiased bootstrap to classify the isolates and establish their cluster membership and e-BURST, was used for establishing clonal complexes (CC). Both approaches involved using representative MLST data from the 18 traditional C. albicans clades, as well as C. albicans-associated and minor species. Ten atypical isolates were distributed as follows: 6/10 (B71, B41, B60, R6, R41, and R282) were grouped into a statistically well-supported atypical cluster (AC) and constituted a differentiated CC 6; 2/10 of the isolates were clearly grouped in clade 1 and were concurrent in CC 4 (B80, B44). Another 2/10 atypical isolates were grouped in clade 10 and concurred in CC 7 (R425, R111); most atypical isolates were related to geographically distant isolates and some represented new ST. Isolates B41 and R41 in the AC had greater virulence. Isolate B44 was fluconazole-resistant and was grouped in clade 1. The atypical nature of the isolates studied here was demonstrated by the contrast between phenotypical traits (C. africana-like), molecular markers (C. albicans-like), virulence, and antifungal resistance, highlighting the widely described genetic plasticity for this genus. Our results showed that the atypical isolates forming well-differentiated groups belonged to C. albicans. Our findings could contribute towards developing molecular epidemiology approaches for managing hospital-acquired infection.

Synergistic Antifungal Activity of Chitosan with Fluconazole against Candida albicans, Candida tropicalis, and Fluconazole-Resistant Strains

(1) Background: Few antifungal drugs are currently available, and drug-resistant strains have rapidly emerged. Thus, the aim of this study is to evaluate the effectiveness of the antifungal activity from a combinational treatment of chitosan with a clinical antifungal drug on Candida albicans and Candida tropicalis. (2) Methods: Minimum inhibitory concentration (MIC) tests, checkerboard assays, and disc assays were employed to determine the inhibitory effect of chitosan with or without other antifungal drugs on C. albicans and C. tropicalis. (3) Results: Treatment with chitosan in combination with fluconazole showed a great synergistic fungicidal effect against C. albicans and C. tropicalis, but an indifferent effect on antifungal activity when challenged with chitosan-amphotericin B or chitosan-caspofungin simultaneously. Furthermore, the combination of chitosan and fluconazole was effective against drug-resistant strains. (4) Conclusions: These findings provide strong evidence that chitosan in combination with fluconazole is a promising therapy against two Candida species and its drug-resistant strains.

Association between CAI microsatellite, multilocus sequence typing, and clinical significance within Candida albicans isolates

Candida albicans bloodstream infection (BSI) is epidemiologically important because of its increasing frequency and serious outcome. Strain typing and delineation of the species are essential for understanding the phylogenetic relationship and clinical significance. Microsatellite CAI genotyping and multilocus sequence typing (MLST) were performed on 285 C. albicans bloodstream isolates from patients in Chang Gung Memorial Hospital at Linkou (CGMHL), Taiwan from 2003 to 2011. Data regarding demographics, comorbidities, risk factors, and clinical outcomes were recorded within adult patients with C. albicans BSI. Both CAI genotyping and MLST yielded comparable discriminatory power for C. albicans characterization. Besides, the distribution of CAI repetition showed a satisfactory phylogenetic association, which could be a good alternative method in the molecular phylogenetics of C. albicans and epidemiological studies. As for the clinical scenario, clade 17 isolates with CAI alleles either possessing 29 or more repetitions were related to higher 14-day and 30-day mortality, and shorter median survival days.

Molecular epidemiology of Candida tropicalis isolated from urogenital tract infections

Candida tropicalis is a common human pathogenic yeast, and its molecular typing is important for studying the population structure and epidemiology of this opportunistic yeast, such as epidemic genotype, population dynamics, nosocomial infection, and drug resistance surveillance. In this study, the antifungal susceptibility test and multilocus sequence typing (MLST) analysis were carried out on C. tropicalis from central China. Among 64 urogenital isolates, 45 diploid sequence types (DST) were found, of which 20 DSTs (44.4%) were new to the central database. The goeBURST analysis showed that CC1 (clonal complex) was the only azole‐resistant (100%, 10/10) cluster in Wuhan, which was composed of DST546, DST225, DST376, and DST506, and most of the strains (90%, 9/10) were isolated from the urinary tract. Potential nosocomial infections were mainly caused by CC1 strains. The azole resistance rate of urinary isolates (50.0%, 21/42) was higher than that of vaginal isolates (27.3%, 6/22). The genotype diversity and novelty of vaginal isolates were higher than those of urinary isolates. C. tropicalis population in Wuhan was genetically diverse and divergent from that seen in other countries. In this study, there were significant differences in genotype and azole susceptibility between urine and vaginal strains. The azole‐resistant cluster (CC1) found in urine is of great significance for the clinical treatment and prevention of nosocomial infection. The newly discovered DSTs will contribute to further study the similarity, genetic relationship, and molecular epidemiology of C. tropicalis worldwide.

Comparison of antifungal and cytotoxicity activities of titanium dioxide and zinc oxide nanoparticles with amphotericin B against different Candida species: In vitro evaluation

BACKGROUND

Candida species are known to cause serious fungal infections that produce cutaneous, mucosal, and systemic infections. Nowadays, mortality and morbidity candidiasis in immunocompromised patients have increased. Nanotechnology is a new world-known technology and includes particles ranging from about 1 to 100 nanometers. The purpose of this study was to evaluate the antifungal and cytotoxicity activities of titanium dioxide nanoparticles (TiO2-NPs) and zinc oxide nanoparticles (ZnO-NPs) compared to amphotericin B (AmB) on different Candida spp in in vitro conditions.

METHODS

In the present study, susceptibility of different Candida species to TiO2-NPs and ZnO-NPs compared to AmB was determined by broth microdilution (BMD) and agar well diffusion methods. Cytotoxicity of TiO2-NPs and ZnO-NPs and amphotericin B was measured by MTT (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium Bromide) assay.

RESULTS

The results indicated that the TiO2-NPs and ZnO-NPs showed antifungal activities against pathogenic Candida spp. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of TiO2-NP ranges against Candida spp. were 128-256 µg/mL and 256-512 µg/mL, respectively. The MIC and MFC values of ZnO-NPs were 64-128 µg/mL and 256-512 µg/mL, respectively. However, MICs and MFCs of AmB were 8-16 µg/mL and 16-32 µg/mL, respectively. The MTT assay results showed that the CC50% belonged to ZnO-NPs 706.2 μg/mL, for TiO2-NPs 862.1 μg/mL, and for AmB 70.19 μg/mL, respectively.

CONCLUSION

Our findings showed that TiO2-NPs and ZnO-NPs had antifungal effects against all Candida species, yet the antifungal properties of TiO2-NPs and ZnO-NPs were significantly less than those of AmB. The CC50% of AmB was significantly lower than ZnO-NPs and TiO2-NPs.

The Paralogous Transcription Factors Stp1 and Stp2 of Candida albicans Have Distinct Functions in Nutrient Acquisition and Host Interaction

Nutrient acquisition is a central challenge for all organisms. For the fungal pathogen Candida albicans, utilization of amino acids has been shown to be critical for survival, immune evasion, and escape, while the importance of catabolism of host-derived proteins and peptides in vivo is less well understood. Stp1 and Stp2 are paralogous transcription factors (TFs) regulated by the Ssy1-Ptr3-Ssy5 (SPS) amino acid sensing system and have been proposed to have distinct, if uncertain, roles in protein and amino acid utilization. We show here that Stp1 is required for proper utilization of peptides but has no effect on amino acid catabolism. In contrast, Stp2 is critical for utilization of both carbon sources. Commensurate with this observation, we found that Stp1 controls a very limited set of genes, while Stp2 has a much more extensive regulon that is partly dependent on the Ssy1 amino acid sensor (amino acid uptake and catabolism) and partly Ssy1 independent (genes associated with filamentous growth, including the regulators UME6 and SFL2). The ssy1Δ/Δ and stp2Δ/Δ mutants showed reduced fitness in a gastrointestinal (GI) colonization model, yet induced greater damage to epithelial cells and macrophages in a manner that was highly dependent on the growth status of the fungal cells. Surprisingly, the stp1Δ/Δ mutant was better able to colonize the gut but the mutation had no effect on host cell damage. Thus, proper protein and amino acid utilization are both required for normal host interaction and are controlled by an interrelated network that includes Stp1 and Stp2.

Analyzing the Association between Candida Prevalence, Species Specificity, and Oral Squamous Cell Carcinoma: A Systematic Review and Meta-Analysis— Candida and OSCC

The present review is a qualitative and quantitative analysis of the overall prevalence of Candida, and its species specificity in oral squamous cell carcinoma (OSCC). PubMed, Scopus, and Web of Science databases were searched using the keywords ‘Candida and oral squamous cell carcinoma’. Only case-control observational studies in the English language evaluating the prevalence and species specificity of Candida in OSCC were included. 297 articles were identified (PubMed-106, Scopus-148, Web of Science-43) using the keywords. After screening the titles and abstracts, 206 articles were removed as they were duplicates (118) or irrelevant to the topic (88). Full text of the remaining 91 articles was assessed using the inclusion criteria, based on which only seven articles were included in the systematic review. For the quantitative analysis, the odds ratio and confidence interval were assessed and a forest plot was generated. Based on the meta-analysis, there is an association between the total Candida, Candida albicans (CA) and OSCC, while the association with non-Candida albicans (NCA) is relatively weak. The number of studies included in the meta-analysis was relatively low (four to five). Further, at least one of the studies included in the meta-analysis for the association of CA., NCA and total Candida with OSCC had a Newcastle–Ottawa score below 7. Thus, although the results showed an association, the quality and quantity of the evidence may not be sufficient for conclusive inference.

The effects of human lactoferrin in experimentally induced systemic candidiasis

Introduction. Candida albicans is responsible for several types of oral and systemic infections. In light of emerging resistance to antifungals, studies have demonstrated the antifungal effect of lactoferrin (LF), which is part of the innate immune system, has anticandidal activities.Methodology. C. albicans (2×10⁶ c.f.u. ml^-1) were incubated either with PBS or human LF (hLF) (100 µg ml^-1) at 37 °C for 24 h and then RNA was isolated and virulence factors analysed. C. albicans (1×10⁵ c.f.u.) was injected into the tail vein of immunocompromised wild-type and Ltf ^-/-. Then, 24 h later, the Ltf ^-/-I mice received hLF intravenously (100 µg g^-1 body weight), while the control group received PBS. Then, 48 h later, the organs were collected, homogenized and C. albicans c.f.u.s were counted. In addition, the inflammatory mediators of kidneys and the virulence factors of C. albicans were analysed.Results. hLF-treated Ltf ^-/-I mice showed significant clearance of C. albicans in different organ tissues when compared to untreated Ltf ^-/-I mice. The inflammatory cytokines, such as IL-1β, IL-6 , TNF-α and MPO and iNOS were downregulated in hLF-treated Ltf ^-/-I mice when compared to untreated Ltf ^-/-I mice. Whereas, IL-10 and IL-17A were upregulated at 72 h post infection when compared to Ltf ^-/-C mice. Histological analysis also revealed a significant decrease in the size and number of infectious foci in the hLF-treated groups. hLF treatment significantly downregulated several virulence factors of C. albicans both in vitro and in vivo.Conclusion. We concluded that hLF-treated Ltf ^-/- mice can reduce the severity of C. albicans-induced systemic infection.

Looking for New Antifungal Drugs from Flavonoids: Impact of the Genetic Diversity of Candida albicans on the in-vitro Response

BACKGROUND

In an era in which antimicrobial resistance is increasing at an alarming pace, it is very important to find new antimicrobial agents effective against pathogenic microrganisms resistant to traditional treatments. Among the notable breakthroughs in the past years of research in natural-drug discovery, there is the identification and testing of flavonoids, a group of plant-derived substances capable of promoting many beneficial effects on humans. These compounds show different biological activities such as inhibition of neuroinflammation and tumor growth as well as antimicrobial activity against many microbial pathogens.

METHODS

We undertook a review of protocols and standard strains used in studies reporting the inhibitory effects of flavonoids against Candida albicans by focusing our attention on genetic characterization of the strains examined. Moreover, using the C. albicans MLST-database, we performed a phylogenetic analysis showing the genetic variation occurring in this species.

RESULTS

Today, we have enough information to estimate genetic diversity within microbial species and recent data revealed that most of fungal pathogens show complex population structures in which not a single isolate can be designated as representative of the entire taxon. This is especially true for the highly divergent fungal pathogen C. albicans, in which the assumption that one or few "standard strains" can represent the whole species is overly unrealistic and should be laid to rest.

CONCLUSION

The goal of this article is to shed light on the extent of genetic variation in C. albicans and how this phenomenon can largely influence the activity of flavonoids against this species.

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.

Upregulation of secreted aspartyl proteinase genes of fluconazole-sensitive Candida albicans isolates

Candida albicans infection development depends on several factors associated with this etiological agent, including secreted aspartyl protease (Sap) production. Sap expression commonly occurs under selective pressure caused by the presence of antifungals. Fluconazole is the main antifungal drug used for treatment or prophylaxis. This study investigated the influence of inhibitory and sub-inhibitory fluconazole concentrations on Sap activity and their gene transcription for three clinical C. albicans isolates. Two isolates presented significant increases in Sap activity and transcription of SAP 1-8 genes in the presence of 1 MIC₈₀ of fluconazole compared to the absence of the antifungal agent. The results suggest that the increase in Sap activity occurs due to an upregulation of the SAP gene transcription influenced by fluconazole. This suggests the importance of all SAP genes in the progression of bloodstream infections compared to primary tissue infection. However, this phenomenon does not occur everywhere, and it is multifactorial. This may be related to the selective pressure effect on transcription modulators. Although preliminary, these results open a new perspective for the study of virulence factors.

Genetic diversity and antifungal susceptibility of Candida albicans isolated from Iranian patients

A total of 105 independent Candida albicans strains isolated from patients in Iran were investigated. According to CLSI documents M27-A3 and M27-S4, the 24 h geometric mean MICs of caspofungin, itraconazole, and fluconazole were 0.27, 3.19, and 11.91 μg/ml, respectively. Microsatellites analysis of CEF3, CAIII, LOC4 Loci identified 93 different allelic genotypes clustered apart into six different clades. Antifungal susceptibility was not linked with the source of isolation and the corresponding genotype of C. albicans strains.

The extremely halotolerant black yeast Hortaea werneckii - a model for intraspecific hybridization in clonal fungi

The polymorphic black yeast Hortaea werneckii (Capnodiales, Ascomycota) is extremely halotolerant (growth from 0 to 30% [w/v] NaCl) and has been extensively studied as a model for halotolerance in Eukaryotes for over two decades. Its most frequent sources are hypersaline environments and adjacent sea-water habitats in temperate, subtropical and tropical climates. Although typically saprobic, H. werneckii can also act as a commensal coloniser on human skin, causing tinea nigra on hands and soles. Here, we report that addition of NaCl to culture media expands the growth range of H. werneckii to 37 °C, which explains its colonisation of human skin, with its increased salinity. The morphological and physiological plasticity/ versatility of H. werneckii indicate that a species complex might be involved. This was investigated in this polyphasic taxonomic analysis based on the global diversity of H. werneckii strains collected from hypersaline environments, and from humans and animals. Analysis of D1/D2domains of 28S and internal transcribed spacer rDNA revealed 10 and 17 genotypes, respectively, that were not always compliant. The genotypes have global distributions. Human and environmental strains with the same genotypes are intermingled. Due to the limited number of phylogenetically informative characters in the ribosomal DNA dataset, the partial genes encoding for β-tubulin (BTB) and mini-chromosome maintenance protein (MCM7) were also sequenced. The use of these genes was hampered by ambiguous sequences obtained by Sanger sequencing, as a consequence of the diploid and highly heterozygous genome of many H. werneckii strains. Analysis of the BTB and MCM7 genes showed that in some cases two copies of the gene from the same genome are positioned in distant phylogenetic clusters of the intraspecific gene tree. Analysis of whole-genome sequences of selected H. werneckii strains generally confirmed the phylogenetic distances estimated on the basis of ribosomal genes, but also showed substantial reticulation within the phylogenetic history of the strains. This is in line with the hypothesis that the diploid genomes of H. werneckii were formed by hybridizations, which have sometimes occurred between relatively divergent strains.

The antimicrobial photodynamic inactivation resistance of Candida albicans is modulated by the Hog1 pathway and the Cap1 transcription factor

Candida albicans is the most important fungal pathogen afflicting humans, particularly immunocompromised patients. However, currently available antifungal drugs are limited and ineffective against drug-resistant strains. The development of new drugs or alternative therapeutic approaches to control fungal infections is urgent and necessary. Photodynamic inactivation (PDI) is a new promising therapy for eradicating microorganism infections through combining visible light, photosensitizers, and oxygen to generate reactive oxygen species (ROS). Although cytoprotective responses induced by photodynamic therapy (PDT) have been well studied in cancer cells, the mechanisms by which C. albicans responds to PDI are largely unknown. In this study, we first demonstrated that PDI induces C. albicans Hog1p activation. Deletion of any of the SSK2, PBS2, and HOG1 genes significantly decreased the survival rate after photochemical reactions, indicating that the Hog1 SAPK pathway is required for tolerance to PDI. Furthermore, the basic leucine zipper transcription factor Cap1 that regulates several downstream antioxidant genes was highly expressed during the response to PDI, and loss of CAP1 also resulted in decreased C. albicans survival rates. This study demonstrates the importance of the Hog1 SAPK and the Cap1 transcription factor, which regulates in resistance to PDI-mediated oxidative stress in C. albicans. Understanding the mechanisms by which C. albicans responds to PDI and consequently scavenges ROS will be very useful for the further development of therapeutics to control fungal infectious diseases, particularly those of the skin and mucosal infections.

Dissecting the Heterogeneous Population Genetic Structure of Candida albicans: Limitations and Constraints of the Multilocus Sequence Typing Scheme

Candida albicans is a fungal opportunistic pathogen of significant public health importance mainly due to the recent emergence of strains with increased aggressiveness and antifungal resistance. Here, we aimed to describe the epidemiological profiles and approximate the population structure of C. albicans by analyzing the C. albicans multilocus sequence typing (MLST) database (Calb-MLST-DB), which contains the largest publically available dataset for this species. Based on 4,318 database isolates, we confirmed the ubiquitous nature of C. albicans including a group of diploid sequence types (DSTs) obtained from Healthy individuals exclusively (taken as an indicator of lack of association with illnesses in its host), until isolates established from Non-Healthy individuals (potentially associated with pathogenic processes) and other DSTs reported in both types (Healthy and Non-Healthy). The highest number of reported DSTs was related to blood, oral and vaginal swabs (32.4, 20.5, and 13.8%, respectively). High genetic diversity was observed in the seven housekeeping genes included in the MLST scheme, with a diverse population structure (154 clonal complexes, CCs; and a high number of singletons, n = 1,074). Phylogenetic reconstruction on the concatenated alignment of these housekeeping genes for all the reported DSTs (n = 3,483) was partially concordant with the CC assignment, however, an absence of bootstrap threshold supported nodes or p-distance, and the lack of association with the other epidemiological variables, evidenced the limitations of the MLST scheme. Marked genetic admixture signals were identified by STRUCTURE, with the majority being attributable to recombination events according to the RDP program results, although another type of exchange event cannot be ruled out. Our results reaffirm the genetic diversity inherent in the genes used for the MLST scheme, which are associated with the chromosomal remodeling already proposed for C. albicans. This was also corroborated with an internal validation at a micro geographical scale. Despite these results are biased due to the unavailability of considering the broad global spectrum of C. albicans isolates around the world. This suggests that the strategy used to population type this pathogen should be reevaluated to improve epidemiological monitoring of its health impact.

Cell wall mannoprotein of Candida albicans polarizes macrophages and affects proliferation and apoptosis through activation of the Akt signal pathway

Candida albicans is a commensal fungus that associates with human hosts. Under normal circumstances this interaction does not produce any severe life-threatening disease, as macrophages of the innate immune system will result in its clearance. However, disorders may arise in immunosuppressed individuals. To understand the bioactivity of Candida albicans cell wall polysaccharides, which represent an important component of its function, mannoprotein from this fungus was extracted, purified and analyzed. Mannoprotein with α-(1,2) and α-(1,6) linkages was investigated with use of HPLC and NMR. Co-incubation of mannoprotein with macrophages resulted in a mannoprotein with the potential to polarize macrophages to M1 and promote phagocytosis/microbial killing ability thus increasing the clearance of pathogens through Akt2. Moreover, mannoprotein within the cell wall promoted cell proliferation and inhibited apoptosis by activation of the Akt signaling pathway. Collectively, α-(1,6)(1,2)-mannoprotein, one of the five polysaccharides extracted from the cell wall of Candida albicans, demonstrates immune-enhancing effects by activation of the Akt signaling pathway. These findings provide important new insights into the biological effects of polysaccharides on macrophages. Such information can then serve as the foundation for the development of novel anti-fungal medications.

DST659 genotype of Candida albicans showing positive association between biofilm formation and dominance in Taiwan

Based on multiple locus sequence typing, we previously found that DST659 and DST693 were dominant genotypes of Candida albicans among the bloodstream isolates at Chang-Gung Memorial Hospital at Linkou. Biofilm-forming activity, which is critical for C. albicans virulence, probably contributed to the dominance of antifungal sensitive isolates in hospital. Both in vitro membrane weighting and in vivo zebrafish egg infection assays were used to evaluate the biofilm-forming activity of DST659 and DST693 genotypes. Medical records of the patients infected by these two genotypes were retrospectively reviewed. High biofilm-forming activity of DST659 isolates was demonstrated in vitro and further proved with the zebrafish egg infection model, which showed a positive correlation between the biofilm-forming extent on chorion and the in vitro biofilm activity. Moreover, significantly less embryos survived when infected with DST659 isolates than those with DST693 (1.25% vs. 11.43%), and the high-biofilm subset of DST659 showed a greater reduction in survival of embryos at 48 h post-infection than the low-biofilm subset (0 vs. 1.92%). Patients infected with DST659 seemed to survive slightly worse than those infected with DST693, although the difference was insignificant. It is noteworthy that DST659-infected patients were associated with a higher incidence in renal insufficiency as compared to those with DST693, the low biofilm genotype. We suggest that a strong biofilm activity of DST659 contributed to a high mortality rate in zebrafish hosts and poor renal function in patients, as well as gaining the dominance in the northern Taiwan.

Unveiling the Multilocus Sequence Typing (MLST) Schemes and Core Genome Phylogenies for Genotyping Chlamydia trachomatis

Multilocus sequence typing (MLST) has become a useful tool for studying the genetic diversity of important public health pathogens, such as Chlamydia trachomatis (Ct). Four MLST schemes have been proposed for Ct (data available from Chlamydiales MLST databases). However, the lack of a sole standardized scheme represents the greatest limitation regarding typing this species. This study was thus aimed at evaluating the usefulness of the four MLST schemes available for Ct, describing each molecular marker's pattern and its contribution toward a description of intra-specific genetic diversity and population structure. The markers for each scheme, showed a variable power of dicrimination, exhibiting in some cases over estimation in the determination of Sequence Types (STs). However, individual analysis of each locus's typing efficiency and discrimination power led to identifying 8 markers as having a suitable pattern for intra-specific typing. analyzing the 8 candidate markers gave a combination of 3 of these loci as an optimal scheme for identifying a large amount of STs, maximizing discrimination power whilst maintaining suitable typing efficiency. One scheme was compared against core genome phylogenies, finding a higher typing resolution through the last approach. These results confirm once again that although complete genome data, in particular from core genome MLST (cgMLST) allow a high resolution clustering for Ct isolates. There are combinations of molecular markers that could generate equivalent results, with the advantage of representing an easy implementation strategy and lower costs leading to contribute to the monitoring and molecular epidemiology of Ct.

Inherited CARD9 Deficiency: Invasive Disease Caused by Ascomycete Fungi in Previously Healthy Children and Adults

Autosomal recessive CARD9 deficiency underlies life-threatening, invasive fungal infections in otherwise healthy individuals normally resistant to other infectious agents. In less than 10 years, 58 patients from 39 kindreds have been reported in 14 countries from four continents. The patients are homozygous (n = 49; 31 kindreds) or compound heterozygous (n = 9; 8 kindreds) for 22 different CARD9 mutations. Six mutations are recurrent, probably due to founder effects. Paradoxically, none of the mutant alleles has been experimentally demonstrated to be loss-of-function. CARD9 is expressed principally in myeloid cells, downstream from C-type lectin receptors that can recognize fungal components. Patients with CARD9 deficiency present impaired cytokine and chemokine production by macrophages, dendritic cells, and peripheral blood mononuclear cells and defective killing of some fungi by neutrophils in vitro. Neutrophil recruitment to sites of infection is impaired in vivo. The proportion of Th17 cells is low in most, but not all, patients tested. Up to 52 patients suffering from invasive fungal diseases (IFD) have been reported, with ages at onset of 3.5 to 52 years. Twenty of these patients also displayed superficial fungal infections. Six patients had only mucocutaneous candidiasis or superficial dermatophytosis at their last follow-up visit, at the age of 19 to 50 years. Remarkably, for 50 of the 52 patients with IFD, a single fungus was involved; only two patients had IFDs due to two different fungi. IFD recurred in 44 of 45 patients who responded to treatment, and a different fungal infection occurred in the remaining patient. Ten patients died from IFD, between the ages of 12 and 39 years, whereas another patient died at the age of 91 years, from an unrelated cause. At the most recent scheduled follow-up visit, 81% of the patients were still alive and aged from 6.5 to 75 years. Strikingly, all the causal fungi belonged to the phylum Ascomycota: commensal Candida and saprophytic Trychophyton, Aspergillus, Phialophora, Exophiala, Corynesprora, Aureobasidium, and Ochroconis. Human CARD9 is essential for protective systemic immunity to a subset of fungi from this phylum but seems to be otherwise redundant. Previously healthy patients with unexplained invasive fungal infection, at any age, should be tested for inherited CARD9 deficiency.

KEY POINTS

• Inherited CARD9 deficiency (OMIM #212050) is an AR PID due to mutations that may be present in a homozygous or compound heterozygous state. • CARD9 is expressed principally in myeloid cells and transduces signals downstream from CLR activation by fungal ligands. • Endogenous mutant CARD9 levels differ between alleles (from full-length normal protein to an absence of normal protein). • The functional impacts of CARD9 mutations involve impaired cytokine production in response to fungal ligands, impaired neutrophil killing and/or recruitment to infection sites, and defects of Th17 immunity. • The key clinical manifestations in patients are fungal infections, including CMC, invasive (in the CNS in particular) Candida infections, extensive/deep dermatophytosis, subcutaneous and invasive phaeohyphomycosis, and extrapulmonary aspergillosis. • The clinical penetrance of CARD9 deficiency is complete, but penetrance is incomplete for each of the fungi concerned. • Age at onset is highly heterogeneous, ranging from childhood to adulthood for the same fungal disease. • All patients with unexplained IFD should be tested for CARD9 mutations. Familial screening and genetic counseling should be proposed. • The treatment of patients with CARD9 mutations is empirical and based on antifungal therapies and the surgical removal of fungal masses. Patients with persistent/relapsing Candida infections of the CNS could be considered for adjuvant GM-CSF/G-CSF therapy. The potential value of HSCT for CARD9-deficient patients remains unclear.

Antifungal tolerance is a subpopulation effect distinct from resistance and is associated with persistent candidemia

Tolerance to antifungal drug concentrations above the minimal inhibitory concentration (MIC) is rarely quantified, and current clinical recommendations suggest it should be ignored. Here, we quantify antifungal tolerance in Candida albicans isolates as the fraction of growth above the MIC, and find that it is distinct from susceptibility/resistance. Instead, tolerance is due to the slow growth of subpopulations of cells that overcome drug stress more efficiently than the rest of the population, and correlates inversely with intracellular drug accumulation. Many adjuvant drugs used in combination with fluconazole, a widely used fungistatic drug, reduce tolerance without affecting resistance. Accordingly, in an invertebrate infection model, adjuvant combination therapy is more effective than fluconazole in treating infections with highly tolerant isolates and does not affect infections with low tolerance isolates. Furthermore, isolates recovered from immunocompetent patients with persistent candidemia display higher tolerance than isolates readily cleared by fluconazole. Thus, tolerance correlates with, and may help predict, patient responses to fluconazole therapy.

The authors show that antifungal tolerance, defined as the fraction of growth of a fungal pathogen above the minimal inhibitory concentration, is due to the slow growth of subpopulations of cells that overcome drug stress, and that high tolerance is often associated with persistent infections.

Deep breast pain during lactation: a case-control study in Sweden investigating the role of Candida albicans

Background

Deep breast pain during lactation, with or without accompanying nipple pain and soreness continues to be anecdotally linked to infection by Candia albicans despite lack of robust evidence in the literature that Candida albicans is the cause of women’s breast symptoms.

Methods

A case-control study of breastfeeding women in Sweden with (n 35) and without (n 35) symptoms that may be attributable to Candida albicans was carried out. The symptoms were radiating, burning and penetrating or non-penetrating breast pain with or without associated nipple pain during or after breastfeeding. The primary aim of the study was to test the hypothesis that breastfeeding women with symptoms commonly associated with Candida albicans infection will have a growth of Candida albicans in their breast milk significantly more often than women without these symptoms. A secondary aim was comparison of breastfeeding self-efficacy, measured by the BSES-SF (Breastfeeding Self Efficacy Scale –Short Form), between cases and controls.

Results

None of the women in the control group and eight of the women in the case group showed a growth of Candida albicans in their breast milk (p <  0.01), which confirms the hypothesis. There were no statistically significant differences in severity or type of symptoms between those in the case group with and without growth of Candida albicans in their breast milk. Results of the BSES-SF measurement showed no statistically significant differences between cases and controls. However, when analyses were stratified for parity, multiparous controls showed statistically significant higher scores for breastfeeding self-efficacy than multiparous cases.

Conclusions

Neither clinical symptoms nor microbial cultivation appear to be reliable means for making a diagnosis of Candida albicans infection of the breast. Skilled breastfeeding consultants should offer support and help with positioning, attachment and identification of physical impediments to successful breastfeeding. Professionals should be aware that it is possible that uncertainty in the breastfeeding situation may to some extent account for mothers’ breast symptoms. The ISRCTN (International Standard Randomised Controlled Trial Number) identity for this case-control study is ISRCTN88839993. The study was retrospectively registered on 30 November 2016.