Pandora's mycological box: molecular sequences vs. morphology in understanding fungal relationships and biodiversity

Fusarium Keratitis From a Comprehensive Eye Health Care Facility in South India: Molecular Characterization by MALDI-TOF Versus PCR Sequencing, Species Complex Distribution, and Clinical Correlation

PURPOSE

Fusarium keratitis possesses significant diagnostic and therapeutic challenges. Medically relevant Fusaria belong to various species complexes and show prominent differences in their antifungal susceptibility profile which may influence the clinical outcome. Rapid diagnostic methods are warranted for precise identification of species complexes for prompt initiation of correct antifungals. The aim of the study was to compare between matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and PCR sequencing for correct species-level identification and to analyze the clinical outcome among different Fusarium species complexes.

METHODS

Twenty-nine culture-proven Fusarium keratitis cases were included in this study. A phylogenetic tree was constructed after TEF1α gene sequencing and isolates were subjected to MALDI-TOF MS, followed by database expansion and identification. Clinical outcome and risk association among species complexes were analyzed retrospectively.

RESULTS

Maximum likelihood phylogeny categorized 68.9% isolates as Fusarium solani species complex (FSSC), 17.2% as Fusarium dimerum species complex (FDSC), followed by 13.7% as Fusarium fujikuroi species complex (FFSC). With extended database, MALDI-TOF MS could correctly speciate 96.5% (28/29) isolates. Previous antibiotic usage (P = 0.034) and preoperative antifungal treatment with natamycin, voriconazole, or ketoconazole (P = 0.025) were significantly higher in the FSSC group. The patients in the FFSC group had a significantly longer duration of symptoms at the time of clinical presentation to the clinic (15 days vs. 5 days, P = 0.030). Among 11 patients with a clinically poor outcome, 9 (31%) had FSSC infection.

CONCLUSIONS

Patients infected with the FSSC had more aggressive infection with poor prognosis. MALDI-TOF MS can serve as the best alternative method to conventional molecular identification with reduced turnaround time, which may help the ophthalmologists to consider the appropriate antifungals or early surgical intervention for improved outcome.

Application of MALDI-TOF MS to species complex differentiation and strain typing of food related fungi: Case studies with Aspergillus section Flavi species and Penicillium roqueforti isolates

Filamentous fungi are one of the main causes of food losses worldwide and their ability to produce mycotoxins represents a hazard for human health. Their correct and rapid identification is thus crucial to manage food safety. In recent years, MALDI-TOF emerged as a rapid and reliable tool for fungi identification and was applied to typing of bacteria and yeasts, but few studies focused on filamentous fungal species complex differentiation and typing. Therefore, the aim of this study was to evaluate the use of MALDI-TOF to identify species of the Aspergillus section Flavi, and to differentiate Penicillium roqueforti isolates from three distinct genetic populations. Spectra were acquired from 23 Aspergillus species and integrated into a database for which cross-validation led to more than 99% of correctly attributed spectra. For P. roqueforti, spectra were acquired from 63 strains and a two-step calibration procedure was applied before database construction. Cross-validation and external validation respectively led to 94% and 95% of spectra attributed to the right population. Results obtained here suggested very good agreement between spectral and genetic data analysis for both Aspergillus species and P. roqueforti, demonstrating MALDI-TOF applicability as a fast and easy alternative to molecular techniques for species complex differentiation and strain typing of filamentous fungi.

Diagnostic of Fungal Infections Related to Biofilms

Fungal biofilm-related infections, most notably those caused by the Candida and Aspergillus genera, need to be diagnosed accurately and rapidly to avoid often unfavorable outcomes. Despite diagnosis of these infections is still based on the traditional histopathology and culture, the use of newer, rapid methods has enormously enhanced the diagnostic capability of a modern clinical mycology laboratory. Thus, while accurate species-level identification of fungal isolates can be achieved with turnaround times considerably shortened, nucleic acid-based or antigen-based detection methods can be considered useful adjuncts for the diagnosis of invasive forms of candidiasis and aspergillosis. Furthermore, simple, reproducible, and fast methods have been developed to quantify biofilm production by fungal isolates in vitro. In this end, isolates can be categorized as low, moderate, or high biofilm-forming, and this categorization may reflect their differential response to the conventional antifungal therapy. By means of drug susceptibility testing performed on fungal biofilm-growing isolates, it is now possible to evaluate not only the activity of conventional antifungal agents, but also of novel anti-biofilm agents. Despite this, future diagnostic methods need to target specific biofilm components/molecules, in order to provide a direct proof of the presence of this growth phenotype on the site of infection. In the meantime, our knowledge of the processes underlying the adaptive drug resistance within the biofilm has put into evidence biofilm-specific molecules that could be potentially helpful as therapeutic targets. Surely, the successful management of clinically relevant fungal biofilms will rely upon the advancement and/or refinement of these approaches.

Cyphobasidium gen. nov., a new lichen-inhabiting lineage in the Cystobasidiomycetes (Pucciniomycotina, Basidiomycota, Fungi)

Pucciniomycotina is a highly diverse group of fungi, showing a remarkably wide range of lifestyles and ecologies. However, lichen-inhabiting fungi are only represented by a few species included in the genera Chionosphaera and Cystobasidium, and their phylogenetic position has never been investigated. Phylogenetic analyses using the nuclear SSU, ITS, and LSU ribosomal DNA markers reveal that the lichenicolous members of Cystobasidium (C. hypogymniicola, C. usneicola) form a monophyletic group distinct from Cystobasidium and outside the Cystobasidiales. The new genus Cyphobasidium is consequently described to accommodate these lichen-inhabiting species. Cyphobasidium is characterized by producing conspicuous galls on the host lichen thalli, by having distinctive basidia that arise from a thick-walled, cup-like structure, the probasidium, that persists after the senescence of the actual basidium (meiosporangium), and by its lichenicolous occurrence on species of Hypogymnia and Usnea. Cyphobasidium is one of the few representatives of the Cystobasidiomycetes in which the sexual stage predominates in nature, whereas most species in the group are known only from an asexual yeast phase. This is the first time the position of lichen-inhabiting taxa within the Pucciniomycotina is investigated using molecular data.

Rapid identification of clinical members of Fusarium fujikuroi complex using MALDI-TOF MS

Aim: To develop the matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF MS) method for identification of Fusarium species within Fusarium fujikuroi complex for use in clinical microbiology laboratories. Materials & methods: A total of 24 reference and 60 clinical and environmental isolates belonging to the F. fujikuroi complex were subjected to MALDI-TOF MS identification. Protein extracts of Fusarium isolates were obtained using formic acid extraction. Multilocus sequence analysis was used as a gold standard. Results: The MALDI-TOF MS Biotyper correctly identified 93.6% of the strains down to the species level, while the remaining isolates (6.4%) were identified at the genus level when using scores of ≥ 2.0 as cut-off values. Correct identification was obtained despite large intraspecific heterogeneities in MALDI-TOF spectra. Conclusion: MALDI-TOF MS is a rapid identification tool for the recognition of species within F. fujikuroi complex, provided a database is available.

MALDI-TOF mass spectrometry: any use for Aspergilli?

Recently, relentless efforts to develop rapid, cost-effective, and reliable laboratory methods for daily diagnosis of fungal diseases such as aspergillosis appear to be materialized in the relatively new, but revolutionary matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS) technology. As for Aspergilli, MALDI-TOF MS profiling of isolates growing in culture--characteristic protein spectra are obtainable by means of simple and reproducible preanalytical and analytical procedures--ensures that single species within the different sections or complexes can be easily and accurately identified, including species that are morphologically and phylogenetically similar to each other. Thus, resort to longer and more onerous molecular biology techniques is restricted to those cases for which no spectra in the reference fungal database or library are available at the time of analysis. However, it is necessary to interrogate reference libraries composed of spectra that have been obtained using procedures similar to those used to obtain the test isolate's mass spectrum, as well as to continuously update these libraries for enriching them with fungal strains/species not (or not well) represented in their current versions. Compared to mold identification, very limited work was reported on the use of MALDI-TOF MS to perform strain typing or antifungal susceptibility testing for Aspergilli. If these complementing areas will be potentiated in the near future, MALDI-TOF MS could effectively support the clinical microbiology/mycology laboratory in its primary role of assisting either infection control specialists or physicians for the diagnosis and treatment of aspergillosis.

DNA barcoding to map the microbial communities: current advances and future directions

During the last two decades, the DNA barcode development towards microbial community has increased dramatically. DNA barcode development is related to error-free and quick species identification which aid in understanding the microbial biodiversity, as well as the diseases related to microbial species. Here, we seek to evaluate the so-called barcoding initiatives for the microbial communities and the emerging trends in this field. In this paper, we describe the development of DNA marker-based DNA barcoding system, comparison between routine species identification and DNA barcode, and microbial biodiversity and DNA barcode for microbial communities. Two major topics, such as the molecular diversity of viruses and barcode for viruses have been discussed at the same time. We demonstrate the current status and the maker of DNA barcode for bacteria, algae, fungi, and protozoa. Furthermore, we argue about the promises, limitations, and present and future challenges of microbial barcode development.

FunGene-DB: a web-based tool for Polyporales strains authentication

Polyporales are extensively studied wood-decaying fungi with applications in white and green biotechnologies and in medicinal chemistry. We developed an open-access, user-friendly, bioinformatics tool named FunGene-DB (http://www.fungene-db.org). The goal was to facilitate the molecular authentication of Polyporales strains and fruit-bodies, otherwise subjected to morphological studies. This tool includes a curated database that contains ITS1-5.8S-ITS2 rDNA genes screened through a semi-automated pipeline from the International Nucleotide Sequence Database (INSD), and the similarity search BLASTn program. Today, the web-accessible database compiles 2379 accepted sequences, among which 386 were selected as reference sequences (most often fully identified ITS sequences for which a voucher, strain or specimen, has been deposited in a public-access collection). The restriction of the database to one reference sequence per species (or per clade for species complex) allowed most often unequivocal analysis. We conclude that FunGene-DB is a promising tool for molecular authentication of Polyporales. It should be especially useful for scientists who are not expert mycologists but who need to check the identity of strains (e.g. for culture collections, for applied microbiology).

A tool kit for quantifying eukaryotic rRNA gene sequences from human microbiome samples

Eukaryotic microorganisms are important but understudied components of the human microbiome. Here we present a pipeline for analysis of deep sequencing data on single cell eukaryotes. We designed a new 18S rRNA gene-specific PCR primer set and compared a published rRNA gene internal transcribed spacer (ITS) gene primer set. Amplicons were tested against 24 specimens from defined eukaryotes and eight well-characterized human stool samples. A software pipeline https://sourceforge.net/projects/brocc/ was developed for taxonomic attribution, validated against simulated data, and tested on pyrosequence data. This study provides a well-characterized tool kit for sequence-based enumeration of eukaryotic organisms in human microbiome samples.

Recent Taxonomic Developments with Candida and Other Opportunistic Yeasts

Increases in susceptible patient populations and advances in identification methods have resulted in the continued recognition of novel yeasts as agents of human infection. Most of these agents are members of the well-recognized genera Candida, Cryptococcus, Trichosporon, and Rhodotorula. Some of these agents are "cryptic species," members of species complexes, and may not be detectable using classical carbohydrate assimilation-based methods of yeast identification. Such species require DNA- or MALDI-based methods for correct identification, although sporadic isolates may not routinely require delineation to the individual species level. The coming end of the fungal taxonomy rules requiring separate names for sexual and asexual forms of the same fungus will hopefully allow greater clarity, as names for medically important yeast can now be based on the needs of the medical mycology community and the common goal of better communication between laboratory and clinician.

Raman microspectroscopy-based identification of individual fungal spores as potential indicators of indoor contamination and moisture-related building damage

We present an application of Raman microspectroscopy (RMS) for the rapid characterization and identification of individual spores from several species of microfungi. The RMS-based methodology requires minimal sample preparation and small sample volumes for analyses. Hence, it is suitable for preserving sample integrity while providing micrometer-scale spatial resolution required for the characterization of individual cells. We present the acquisition of unique Raman spectral signatures from intact fungal spores dispersed on commercially available aluminum foil substrate. The RMS-based method has been used to compile a reference library of Raman spectra from several species of microfungi typically associated with damp indoor environments. The acquired reference spectral library has subsequently been used to identify individual microfungal spores through direct comparison of the spore Raman spectra with the reference spectral signatures in the library. Moreover, the distinct peak structures of Raman spectra provide detailed insight into the overall chemical composition of spores. We anticipate potential application of this methodology in the fields of public health, forensic sciences, and environmental microbiology.

Food fermentations: microorganisms with technological beneficial use

Microbial food cultures have directly or indirectly come under various regulatory frameworks in the course of the last decades. Several of those regulatory frameworks put emphasis on "the history of use", "traditional food", or "general recognition of safety". Authoritative lists of microorganisms with a documented use in food have therefore come into high demand. One such list was published in 2002 as a result of a joint project between the International Dairy Federation (IDF) and the European Food and Feed Cultures Association (EFFCA). The "2002 IDF inventory" has become a de facto reference for food cultures in practical use. However, as the focus mainly was on commercially available dairy cultures, there was an unmet need for a list with a wider scope. We present an updated inventory of microorganisms used in food fermentations covering a wide range of food matrices (dairy, meat, fish, vegetables, legumes, cereals, beverages, and vinegar). We have also reviewed and updated the taxonomy of the microorganisms used in food fermentations in order to bring the taxonomy in agreement with the current standing in nomenclature.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Current state and perspectives of fungal DNA barcoding and rapid identification procedures

Fungal research is experiencing a new wave of methodological improvements that most probably will boost mycology as profoundly as molecular phylogeny has done during the last 15 years. Especially the next generation sequencing technologies can be expected to have a tremendous effect on fungal biodiversity and ecology research. In order to realise the full potential of these exciting techniques by accelerating biodiversity assessments, identification procedures of fungi need to be adapted to the emerging demands of modern large-scale ecological studies. But how should fungal species be identified in the near future? While the answer might seem trivial to most microbiologists, taxonomists working with fungi may have other views. In the present review, we will analyse the state of the art of the so-called barcoding initiatives in the light of fungi, and we will seek to evaluate emerging trends in the field. We will furthermore demonstrate that the usability of DNA barcoding as a major tool for identification of fungi largely depends on the development of high-quality sequence databases that are thoroughly curated by taxonomists and systematists.