Antimicrobial Susceptibility Testing for Three Malassezia Species.

The Malassezia genus comprises lipid-dependent yeasts that have long been associated with common skin diseases, and have recently been linked with Crohn's disease and certain cancers. Understanding Malassezia susceptibility to diverse antimicrobial agents is crucial for identifying effective antifungal therapies. Here, we tested the efficacy of isavuconazole, itraconazole, terbinafine, and artemisinin against three Malassezia species: M. restricta, M. slooffiae, and M. sympodialis. Using broth microdilution, we found antifungal properties for the two previously unstudied antimicrobials: isavuconazole and artemisinin. Overall, all Malassezia species were particularly susceptible to itraconazole, with a MIC range from 0.007 to 0.110 µg/mL. IMPORTANCE The Malassezia genus is known to be involved in a variety of skin conditions and has recently been associated with diseases such as Crohn's disease, pancreatic ductal carcinoma, and breast cancer. This work was completed to assess susceptibility to a variety of antimicrobial drugs on three Malassezia species, in particular Malassezia restricta, which is an abundant Malassezia species both on human skin and internal organs and has been implicated in Crohn's disease. We tested two previously unstudied drugs and developed a new testing method to overcome current limitations for measuring growth inhibition of slow-growing Malassezia strains.

Malassezia and Parkinson's Disease.

Parkinson's disease (PD) is a common debilitating neurodegenerative disease caused by a loss of dopamine neurons in the substantia nigra within the central nervous system (CNS). The process leading to this neuronal loss is poorly understood. Seborrheic dermatitis (SD) is a common benign inflammatory condition of the skin which mainly affects lipid-rich regions of the head and trunk. SD is caused by over proliferation of the lipophilic fungus Malassezia. PD and SD are strongly associated. The increased PD risk following an SD diagnosis (OR = 1.69, 95% CI 1.36, 2.1; p < 0.001) reported by Tanner and colleagues remains unexplained. Malassezia were historically considered commensals confined to the skin. However, many recent studies report finding Malassezia in internal organs, including the CNS. This raises the possibility that Malassezia might be directly contributing to PD. Several lines of evidence support this hypothesis. AIDS is causally associated with both parkinsonism and SD, suggesting that weak T cell-mediated control of commensal microbes such as Malassezia might contribute to both. Genetic polymorphisms associated with PD (LRRK2, GBA, PINK1, SPG11, SNCA) increase availability of lipids within human cells, providing a suitable environment for Malassezia. Four LRRK2 polymorphisms which increase PD risk also increase Crohn's disease risk; Crohn's disease is strongly associated with an immune response against fungi, particularly Malassezia. Finally, Malassezia hypha formation and melanin synthesis are stimulated by L-DOPA, which could promote Malassezia invasiveness of dopamine neurons, and contribute to the accumulation of melanin in these neurons. Although Malassezia's presence in the substantia nigra remains to be confirmed, if Malassezia play a role in PD etiology, antifungal drugs should be tested as a possible therapeutic intervention.

Spondyloarthritis, Acute Anterior Uveitis, and Fungi: Updating the Catterall-King Hypothesis.

Spondyloarthritis is a common type of arthritis which affects mostly adults. It consists of idiopathic chronic inflammation of the spine, joints, eyes, skin, gut, and prostate. Inflammation is often asymptomatic, especially in the gut and prostate. The HLA-B*27 allele group, which presents intracellular peptides to CD8+ T cells, is by far the strongest risk factor for spondyloarthritis. The precise mechanisms and antigens remain unknown. In 1959, Catterall and King advanced a novel hypothesis explaining the etiology of spondyloarthritis: an as-yet-unrecognized sexually acquired microbe would be causing all spondyloarthritis types, including acute anterior uveitis. Recent studies suggest an unrecognized sexually acquired fungal infection may be involved in prostate cancer and perhaps multiple sclerosis. This warrants reanalyzing the Catterall-King hypothesis based on the current literature. In the last decade, many links between spondyloarthritis and fungal infections have been found. Antibodies against the fungal cell wall component mannan are elevated in spondyloarthritis. Functional polymorphisms in genes regulating the innate immune response against fungi have been associated with spondyloarthritis (CARD9 and IL23R). Psoriasis and inflammatory bowel disease, two common comorbidities of spondyloarthritis, are both strongly associated with fungi. Evidence reviewed here lends credence to the Catterall-King hypothesis and implicates a common fungal etiology in prostate cancer, benign prostatic hyperplasia, multiple sclerosis, psoriasis, inflammatory bowel disease, and spondyloarthritis. However, the evidence available at this time is insufficient to definitely confirm this hypothesis. Future studies investigating the microbiome in relation to these conditions should screen specimens for fungi in addition to bacteria. Future clinical studies of spondyloarthritis should consider antifungals which are effective in psoriasis and multiple sclerosis, such as dimethyl fumarate and nystatin.

The Role of Fungi in the Etiology of Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system. Infectious triggers of MS are being actively investigated. Substantial evidence supports the involvement of the Epstein-Barr virus (EBV), though other viruses, bacteria, protists, and fungi are also being considered. Many links between fungi and diseases involving chronic inflammation have been found recently. Evidence linking MS and fungi is reviewed here. The HLA-DRB1*15 allele group is the most important genetic risk factor of MS, and is a risk factor in several other conditions linked to fungal infections. Many biomarkers of MS are consistent with fungal infections, such as IL-17, chitotriosidase, and antibodies against fungi. Dimethyl fumarate (DMF), first used as an industrial fungicide, was recently repurposed to reduce MS symptoms. Its mechanisms of action in MS have not been firmly established. The low risk of MS during childhood and its moderate association with herpes simplex virus type 2 suggest genital exposure to microbes (including fungi) should be investigated as a possible trigger. Molecular and epidemiological evidence support a role for infections such as EBV in MS. Though fungal infections have not been widely studied in MS, many lines of evidence are consistent with a fungal etiology. Future microbiome and serological studies should consider fungi as a possible risk factor for MS, and future clinical studies should consider the effect of fungicides other than DMF on MS symptoms.

Epstein-Barr virus and multiple sclerosis: Updating Pender's hypothesis.

Substantial epidemiological evidence supports the involvement of the Epstein-Barr virus (EBV) in multiple sclerosis (MS). Mechanisms through which EBV may increase MS risk are reviewed here. Most individuals contract EBV in early childhood yet only develop MS in early adulthood, by which time EBV has been latent for decades. When latent, EBV is confined to a minute subset of memory B cells: about 1000 cells in peripheral blood and 500,000 cells in the lymphoid system, mainly in the mouth. Reactivation of EBV in the central nervous system (CNS) has been proposed as a cause of MS. Alternatively, EBV may enable the recognition of "forbidden" antigens by memory B cells through its presence in this leukocyte type, as first proposed by Pender. Though the requirement for B cells in MS supports both hypotheses, EBV has not been consistently found in MS lesions, as would be expected. EBV episome replication during B cell division is now known to be inefficient, resulting in some descendant B cells becoming EBV-free after a few dozen divisions. EBV-free memory B cells in the CNS may thus have descended from a memory B cell which matured while containing EBV episomes, enabling its B cell receptor to recognize "forbidden" MS-causing antigens in the CNS, even if EBV is absent from this site.

Common contaminants in next-generation sequencing that hinder discovery of low-abundance microbes.

Unbiased high-throughput sequencing of whole metagenome shotgun DNA libraries is a promising new approach to identifying microbes in clinical specimens, which, unlike other techniques, is not limited to known sequences. Unlike most sequencing applications, it is highly sensitive to laboratory contaminants as these will appear to originate from the clinical specimens. To assess the extent and diversity of sequence contaminants, we aligned 57 "1000 Genomes Project" sequencing runs from six centers against the four largest NCBI BLAST databases, detecting reads of diverse contaminant species in all runs and identifying the most common of these contaminant genera (Bradyrhizobium) in assembled genomes from the NCBI Genome database. Many of these microorganisms have been reported as contaminants of ultrapure water systems. Studies aiming to identify novel microbes in clinical specimens will greatly benefit from not only preventive measures such as extensive UV irradiation of water and cross-validation using independent techniques, but also a concerted effort to sequence the complete genomes of common contaminants so that they may be subtracted computationally.

MSMB variation and prostate cancer risk: clues towards a possible fungal etiology.

BACKGROUND. With recent advances in high-throughput sequencing technologies, many prostate cancer risk loci have been identified, including rs10993994, a single nucleotide polymorphism (SNP) located near the MSMB gene. Variant allele (T) carriers of this SNP produce less prostate secretory protein 94 (PSP94), the protein product of MSMB, and have an increased risk of prostate cancer (approximately 25% per T allele), suggesting that PSP94 plays a protective role in prostate carcinogenesis, although the mechanisms for such protection are unclear. METHODS. We reviewed the literature on possible mechanisms for PSP94 protection for prostate cancer. RESULTS. One possible mechanism is tumor suppression, as PSP94 has been observed to inhibit cell or tumor growth in in vitro and in vivo models. Another novel mechanism, which we propose in this review article, is that PSP94 may protect against prostate cancer by preventing or limiting an intracellular fungal infection in the prostate. This mechanism is based on the recent discovery of PSP94's fungicidal activity in low-calcium environments (such as the cytosol of epithelial cells), and accumulating evidence suggesting a role for inflammation in prostate carcinogenesis. We provide further details of our proposed mechanism in this review article. CONCLUSIONS. To explore this mechanism, future studies should consider screening prostate specimens for fungi using the rapidly expanding number of molecular techniques capable of identifying infectious agents from the entire tree of life.