MTL genotypes, phenotypic switching, and susceptibility profiles of Candida parapsilosis species group compared to Lodderomyces elongisporus

Unveiling Lodderomyces elongisporus as an Emerging Yeast Pathogen: A Holistic Approach to Microbiological Diagnostic Strategies

Lodderomyces elongisporus, first isolated in 1952, has increasingly been recognized as a significant pathogen, with a notable rise in human infections since the 1970s. Initially misidentified as Candida parapsilosis due to morphological similarities, L. elongisporus has now been conclusively established as a distinct species, largely due to advancements in molecular biology, particularly DNA sequencing. This review traces the detection history of L. elongisporus, from the earliest documented cases to the most recent reports, underscoring its role as a causative agent in human infections. It also explores therapeutic strategies that have demonstrated efficacy, alongside instances of environmental contamination reported in international literature. A critical evaluation of diagnostic methodologies essential for precise identification is provided, including culture-based techniques such as colony morphology on Sabouraud Dextrose Agar (SDA) and chromogenic media, coupled with microscopic assessments using Lactophenol Cotton Blue (LPCB) and Gram staining. The ultrastructure of L. elongisporus, as observed under Scanning Electron Microscopy (SEM), is also discussed. Furthermore, non-culture-based diagnostics, such as sugar utilization tests (API 20C AUX and the innovative in-house arabinose-based "Loddy" test) and antifungal susceptibility profiling, are reviewed, with a particular focus on molecular tools like ITS-DNA sequencing and MALDI-TOF MS, which, despite their higher costs, offer unparalleled specificity. The accurate distinction and characterization of L. elongisporus are paramount, particularly in vulnerable and immunocompromised patients, where misdiagnosis can lead to severe consequences. This review advocates for intensified research efforts to develop more accessible diagnostic tools and deepen our understanding of this emerging pathogen, ultimately aiming to improve patient outcomes.

Glucose-enhanced oxidative stress resistance-A protective anticipatory response that enhances the fitness of Candida albicans during systemic infection

Most microbes have developed responses that protect them against stresses relevant to their niches. Some that inhabit reasonably predictable environments have evolved anticipatory responses that protect against impending stresses that are likely to be encountered in their niches-termed "adaptive prediction". Unlike yeasts such as Saccharomyces cerevisiae, Kluyveromyces lactis and Yarrowia lipolytica and other pathogenic Candida species we examined, the major fungal pathogen of humans, Candida albicans, activates an oxidative stress response following exposure to physiological glucose levels before an oxidative stress is even encountered. Why? Using competition assays with isogenic barcoded strains, we show that "glucose-enhanced oxidative stress resistance" phenotype enhances the fitness of C. albicans during neutrophil attack and during systemic infection in mice. This anticipatory response is dependent on glucose signalling rather than glucose metabolism. Our analysis of C. albicans signalling mutants reveals that the phenotype is not dependent on the sugar receptor repressor pathway, but is modulated by the glucose repression pathway and down-regulated by the cyclic AMP-protein kinase A pathway. Changes in catalase or glutathione levels do not correlate with the phenotype, but resistance to hydrogen peroxide is dependent on glucose-enhanced trehalose accumulation. The data suggest that the evolution of this anticipatory response has involved the recruitment of conserved signalling pathways and downstream cellular responses, and that this phenotype protects C. albicans from innate immune killing, thereby promoting the fitness of C. albicans in host niches.

Metabolic and phenotypic plasticity may contribute for the higher virulence of Trichosporon asahii over other Trichosporonaceae members

BACKGROUND

The Trichosporonaceae family comprises a large number of basidiomycetes widely distributed in nature. Some of its members, especially Trichosporon asahii, have the ability to cause human infections. This ability is related to a series of virulence factors, which include lytic enzymes production, biofilm formation, resistance to oxidising agents, melanin and glucuronoxylomannan in the cell wall, metabolic plasticity and phenotypic switching. The last two are poorly addressed within human pathogenic Trichosporonaceae.

OBJECTIVE

These factors were herein studied to contribute with the knowledge of these emerging pathogens and to uncover mechanisms that would explain the higher frequency of T. asahii in human infections.

METHODS

We included 79 clinical isolates phenotypically identified as Trichosporon spp. and performed their molecular identification. Lactate and N-acetyl glucosamine were the carbon sources of metabolic plasticity studies. Morphologically altered colonies after subcultures and incubation at 37°C indicated phenotypic switching.

RESULTS AND CONCLUSION

The predominant species was T. asahii (n = 65), followed by Trichosporon inkin (n = 4), Apiotrichum montevideense (n = 3), Trichosporon japonicum (n = 2), Trichosporon faecale (n = 2), Cutaneotrichosporon debeurmannianum (n = 1), Trichosporon ovoides (n = 1) and Cutaneotrichosporon arboriforme (n = 1). T. asahii isolates had statistically higher growth on lactate and N-acetylglucosamine and on glucose during the first 72 h of culture. T. asahii, T. inkin and T. japonicum isolates were able to perform phenotypic switching. These results expand the virulence knowledge of Trichosporonaceae members and point for a role for metabolic plasticity and phenotypic switching on the trichosporonosis pathogenesis.

Mating-Type Switching in Budding Yeasts, from Flip/Flop Inversion to Cassette Mechanisms

Mating-type switching is a natural but unusual genetic control process that regulates cell identity in ascomycete yeasts. It involves physically replacing one small piece of genomic DNA by another, resulting in replacement of the master regulatory genes in the mating pathway and hence a switch of cell type and mating behavior. In this review, we concentrate on recent progress that has been made on understanding the origins and evolution of mating-type switching systems in budding yeasts (subphylum Saccharomycotina). Because of the unusual nature and the complexity of the mechanism in Saccharomyces cerevisiae, mating-type switching was assumed until recently to have originated only once or twice during yeast evolution. However, comparative genomics analysis now shows that switching mechanisms arose many times independently-at least 11 times in budding yeasts and once in fission yeasts-a dramatic example of convergent evolution. Most of these lineages switch mating types by a flip/flop mechanism that inverts a section of a chromosome and is simpler than the well-characterized 3-locus cassette mechanism (MAT/HML/HMR) used by S. cerevisiae. Mating-type switching (secondary homothallism) is one of the two possible mechanisms by which a yeast species can become self-fertile. The other mechanism (primary homothallism) has also emerged independently in multiple evolutionary lineages of budding yeasts, indicating that homothallism has been favored strongly by natural selection. Recent work shows that HO endonuclease, which makes the double-strand DNA break that initiates switching at the S. cerevisiae MAT locus, evolved from an unusual mobile genetic element that originally targeted a glycolytic gene, FBA1.

The first described case of Lodderomyces elongisporus meningitis

We describe the first documented case of meningitis caused by Lodderomyces elongisporus. Identification of L. elongisporus was made on the basis of an arachnoid biopsy with pathology samples sent for fungal internal transcribed spacer sequencing after multiple central nervous system (CNS) fungal culture specimens were negative. After final diagnosis, treatment was transitioned from amphotericin to fluconazole, which, combined with insertion of lumbar drain followed by a permanent ventriculopleural shunt, resulted in significant clinical improvement. Our report reviews the literature of (1) cases of L. elongisporus, which almost exclusively describe fungemia or endocarditis; (2) CNS infections caused by Candida parapsilosis, an organism with which L. elongisporus was previously conflated; and (3) management of fungal meningitis-associated hydrocephalus.

Short communication: Characterization of vaginal fungal communities in healthy women and women with bacterial vaginosis (BV); a pilot study

The role of the vaginal fungal community, the mycobiota, in women's health is an emerging area of research. Utilization of novel molecular technology enables more in-depth characterization and identification of fungal diversity, and their potential associations to health. The present study is a substudy of a larger observational clinical trial investigating the vaginal microbiota composition before and after antibiotic treatment for Bacterial Vaginosis (BV) infection in comparison to the microbiota of healthy women (Clinicaltrials.gov identifier: NCT03187). Here, we characterized the vaginal mycobiota by sequencing the internal transcribed spacer (ITS) 2 region from vaginal microbial DNA collected from healthy women and women with BV and in relation to their treatment with oral metronidazole. Interestingly, both ascomycetous and basidiomycetous yeasts and filamentous fungi consisting of more than 30 different species were detectable from 21 out of 94 vaginal swab samples. The mycobiota was dominated by Candida species (>60% of relative abundance) and especially with Candida albicans in both study groups. The abundance of C. albicans was inversely correlated with fungal diversity but did not correlate with Nugent scores. Metronidazole did not seem to have a major effect on the relative abundance of C. albicans. The results revealed the diversity of the fungal community within healthy and BV-infected women, which is worth exploring further.

Multiple Reinventions of Mating-type Switching during Budding Yeast Evolution

Cell type in budding yeasts is determined by the genotype at the mating-type (MAT) locus, but yeast species differ widely in their mating compatibility systems and life cycles. Among sexual yeasts, heterothallic species are those in which haploid strains fall into two distinct and stable mating types (MATa and MATα), whereas homothallic species are those that can switch mating types or that appear not to have distinct mating types [1, 2]. The evolutionary history of these mating compatibility systems is uncertain, particularly regarding the number and direction of transitions between homothallism and heterothallism, and regarding whether the process of mating-type switching had a single origin [3-5]. Here, we inferred the mating compatibility systems of 332 budding yeast species from their genome sequences. By reference to a robust phylogenomic tree [6], we detected evolutionary transitions between heterothallism and homothallism, and among different forms of homothallism. We find that mating-type switching has arisen independently at least 11 times during yeast evolution and that transitions from heterothallism to homothallism greatly outnumber transitions in the opposite direction (31 versus 3). Although the 3-locus MAT-HML-HMR mechanism of mating-type switching as seen in Saccharomyces cerevisiae had a single evolutionary origin in budding yeasts, simpler "flip/flop" mechanisms of switching evolved separately in at least 10 other groups of yeasts. These results point to the adaptive value of homothallism and mating-type switching to unicellular fungi.

Genetic Diversity and Antifungal Susceptibility of Candida parapsilosis Sensu Stricto Isolated from Bloodstream Infections in Turkish Patients

Candida parapsilosis sensu stricto is an emerging cause of hospital-acquired Candida infections, predominantly in southern Europe, South America, and Asia. We investigated the genetic diversity and antifungal susceptibility profile of 170 independent C. parapsilosis sensu stricto strains obtained from patients with candidemia who were treated at the Ege University Hospital in Izmir, Turkey, between 2006 and 2014. The identity of each strain was confirmed via PCR amplification and digestion of the secondary alcohol dehydrogenase-encoding gene. The 24-h geometric mean minimum inhibitory concentrations of the antifungal agents, in increasing order, were as follows: posaconazole, 0.10 µg/mL; voriconazole, 0.21 µg/mL; caspofungin, 0.38 µg/mL; amphotericin B, 0.61 µg/mL; anidulafungin, 0.68 µg/mL; and fluconazole, 2.95 µg/mL. Microsatellite genotyping of the isolates (using fluorescently labeled primers and a panel of four different short-nucleotide repeat fragments) identified 25, 17, 17, and 8 different allelic genotypes at the CP6, B5, CP4, and CP1 locus, respectively. Posaconazole, caspofungin, and amphotericin B showed the greatest in vitro activity of the tested systemic azole, echinocandin, and polyene agents, respectively, and the observed antifungal susceptibility of the isolates was shown to be independent of their isolation source. We obtained a combined discriminatory power of 0.99 with a total of 130 genotypes for 170 isolates tested. Finally, microsatellite profiling analysis confirmed the presence of identical genotype between separate isolates, supporting that effective surveillance and infection-prevention programs are essential to limit the impact of C. parapsilosis sensu stricto on hospitalized patients' health.