History and Perspective of Immunotherapy for Pythiosis

Ex vivo observation of Pythium insidiosum-antigen treated neutrophils on three Pythium insidiosum strains isolated from vascular pythiosis patients

The mechanisms of Pythium insidiosum-antigen (PIA) immunotherapy activating a patient's immune system are unknown. We evaluated the interleukin-8 (IL-8) serum levels during P. insidiosum infection and after vaccination with PIA in vascular pythiosis cases. Furthermore, we studied the anti-P. insidiosum activity of neutrophils stimulated with various concentrations of PIA ex vivo in 3 strains of P. insidiosum isolated from vascular pythiosis patients. IL-8 serum levels were evaluated using the ELISA technique. We assessed the effect of PIA-stimulated neutrophils on the viability of zoospores using MTT assay, visualized neutrophil extracellular trap (NET) formation via microscopy, and measured the levels of double-stranded DNA (dsDNA) using PicoGreen dsDNA quantitation assay in 3 strains of P. insidiosum isolated from vascular pythiosis patients. Serum levels of IL-8 gradually lowered from the early to the end phases of vaccination with PIA among the surviving group of vascular pythiosis cases. Neutrophils stimulated with 0.01 µg/ml PIA reduced zoospore viability significantly compared to PIA-unstimulated neutrophils for strain 1 and strain 3 (p < .05). Neutrophils stimulated with 0.01, 0.1, 1, and 10 µg/ml PIA exhibited significantly lower zoospore viability than PIA-unstimulated neutrophils for strain 2 (p < .05). IL-8 can be used as a biomarker for monitoring vascular pythiosis cases treated with the PIA vaccine. Also, anti-P. insidiosum activity of PIA-stimulated neutrophils was probably due to the disruption of cellular activity in zoospores rather than the mechanisms based on the formation of NETs.

Treating Pythiosis with Antibacterial Drugs Targeting Protein Synthesis: An Overview

This review article explores the effectiveness of antibacterial drugs that inhibit protein synthesis in treating pythiosis, a difficult-to-treat infection caused by Pythium insidiosum. The article highlights the susceptibility of P. insidiosum to antibacterial drugs, such as macrolides, oxazolidinones, and tetracyclines. We examine various studies, including in vitro tests, experimental infection models, and clinical case reports. Based on our synthesis of these findings, we highlight the potential of these drugs in managing pythiosis, primarily when combined with surgical interventions. The review emphasizes the need for personalized treatment strategies and further research to establish standardized testing protocols and optimize therapeutic approaches.

Subcutaneous pythiosis in human treated successfully with antimicrobial treatment, debridement and immunotherapy

Pythiosis is caused due to a filamentous eukaryotic micro-organism called Pythium insidiosum and the disease occurs commonly in horses and cattle. Subcutaneous pythiosis infection in humans is rare with no clear clinical guidelines for treatment. We present a case of a man in his 20s with non-resolving ulcers noted over lower extremity after exposure to swamp water draining animal remains. The patient received several courses of oral antibiotics with no improvement in symptoms before getting admitted to our institution. A diagnosis of subcutaneous pythiosis was made after deep wound culture following debridement detected P. insidiosum by use of PCR. Due to the rare incidence of such infection in humans and no clear guidelines available for treatment, the case was discussed with infectious disease specialists outside our institution and with veterinary physicians. An emergent approval for use of immunotherapy in conjunction with surgical debridement and antimicrobials was obtained from Food and Drug administration. The patient underwent successful treatment of infection and skin graft following treatment.

Potential anti-Pythium insidiosum therapeutics identified through screening of agricultural fungicides

Pythiosis is a life-threatening infectious disease caused by the oomycete Pythium insidiosum. Clinical manifestations of pythiosis include an eye, blood vessel, skin, or gastrointestinal tract infection. Pythiosis has been increasingly reported worldwide, with an overall mortality rate of 28%. Radical surgery is required to save patients' lives due to the limited efficacy of antimicrobial drugs. Effective medical treatments are urgently needed for pythiosis. This study aims to find anti-P. insidiosum agents by screening 17 agricultural fungicides that inhibit plant-pathogenic oomycetes and validating their efficacy and safety. Cyazofamid outperformed other fungicides as it can potently inhibit genetically diverse P. insidiosum isolates while exhibiting minimal cellular toxicities. The calculated therapeutic scores determined that the concentration of cyazofamid causing significant cellular toxicities was eight times greater than the concentration of the drug effectively inhibiting P. insidiosum. Furthermore, other studies showed that cyazofamid exhibits low-to-moderate toxicities in animals. The mechanism of cyazofamid action is likely the inhibition of cytochrome b, an essential component in ATP synthesis. Molecular docking and dynamic analyses depicted a stable binding of cyazofamid to the Qi site of the P. insidiosum's cytochrome b orthologous protein. In conclusion, our search for an effective anti-P. insidiosum drug indicated that cyazofamid is a promising candidate for treating pythiosis. With its high efficacy and low toxicity, cyazofamid is a potential chemical for treating pythiosis, reducing the need for radical surgeries, and improving recovery rates. Our findings could pave the way for the development of new and effective treatments for pythiosis.IMPORTANCEPythiosis is a severe infection caused by Pythium insidiosum. The disease is prevalent in tropical/subtropical regions. This infectious condition is challenging to treat with antifungal drugs and often requires surgical removal of the infected tissue. Pythiosis can be fatal if not treated promptly. There is a need for a new treatment that effectively inhibits P. insidiosum. This study screened 17 agricultural fungicides that target plant-pathogenic oomycetes and found that cyazofamid was the most potent in inhibiting P. insidiosum. Cyazofamid showed low toxicity to mammalian cells and high affinity to the P. insidiosum's cytochrome b, which is involved in energy production. Cyazofamid could be a promising candidate for the treatment of pythiosis, as it could reduce the need for surgery and improve the survival rate of patients. This study provides valuable insights into the biology and drug susceptibility of P. insidiosum and opens new avenues for developing effective therapies for pythiosis.

MGI short-read genome assemblies of Pythium insidiosum (reclassified as Pythium periculosum) strains Pi057C3 and Pi050C3

OBJECTIVES

Pythium insidiosum causes a difficult-to-treat infectious condition called pythiosis, with high morbidity and mortality. So far, genome data of at least 10 strains of P. insidiosum, primarily classified in the phylogenetic clades I and II, have been sequenced using various next-generation sequencing platforms. The MGI short-read platform was employed to obtain genome data of 2 clade-III strains of P. insidiosum (recently reclassified as Pythium periculosum) from patients in Thailand and the United States. This work is a part of our attempt to generate a comprehensive genome database from diverse pathogen strains.

DATA DESCRIPTION

A 150-bp paired-end library was prepared from a gDNA sample of P. insidiosum (P. periculosum) strains Pi057C3 and Pi050C3 (also known as ATCC90586) to generate draft genome sequences using an MGISEQ-2000RS sequencer. As a result, for the strain Pi057C3, we obtained a 42.5-Mb assembled genome (164x coverage) comprising 14,134 contigs, L50 of 241, N50 of 45,748, 57.6% CG content, and 12,147 ORFs. For the strain Pi050C3, we received a 43.3-Mb draft genome (230x coverage) containing 14,511 contigs, L50 of 245, N50 of 45,208, 57.7% CG content, and 12,249 ORFs. The genome sequences have been deposited in the NCBI/DDBJ databases under the accession numbers JAKCXM000000000.1 (strain Pi057C3) and JAKCXL000000000.1 (strain Pi050C3).

Neutrophil extracellular traps and phagocytosis in Pythium insidiosum

Neutrophils are innate immune cells that play crucial roles in response to extracellular pathogens, including bacteria and fungi. Pythium insidiosum (P insidiosum) is a fungus-like pathogen that causes "pythiosis" in mammals. This study investigated in vitro function of human neutrophils against P. insidiosum. We demonstrated the killing mechanism of neutrophils when incubated with P. insidiosum zoospores (infective stage), such as phagocytosis and neutrophil extracellular traps (NETs). Healthy human neutrophils significantly reduced six strains of live zoospores isolated from different sources compared to the condition without neutrophils (p < 0.001), observed by colony count and trypan blue staining. As our results showed the killing ability of neutrophils, we further investigated the neutrophil killing mechanism when incubating with zoospores. Our study found that only two strains of heat-killed zoospores significantly induced phagocytosis (p < 0.01). Co-culture of heat-killed zoospores and neutrophils demonstrated NET formation, which was detected by immunofluorescence staining using DAPI, anti-myeloperoxidase, and anti-neutrophil elastase and quantitated under the fluorescence microscope. In addition, the level of cell-free DNA released from neutrophils (as a marker of NET production) after incubation with zoospores showed significantly increased levels when compared with unstimulated neutrophils (p < 0.001). Our findings demonstrate that neutrophils revealed the NET formation in response to P. insidiosum zoospores. This study is the first observation of the neutrophil mechanism against P. insidiosum, which could provide a better understanding of some parts of the innate immune response during pythiosis.

Selection of an Appropriate In Vitro Susceptibility Test for Assessing Anti-Pythium insidiosum Activity of Potassium Iodide, Triamcinolone Acetonide, Dimethyl Sulfoxide, and Ethanol

The orphan but highly virulent pathogen Pythium insidiosum causes pythiosis in humans and animals. Surgery is a primary treatment aiming to cure but trading off losing affected organs. Antimicrobial drugs show limited efficacy in treating pythiosis. Alternative drugs effective against the pathogen are needed. In-house drug susceptibility tests (i.e., broth dilution, disc diffusion, and radial growth assays) have been established, some of which adapted the standard protocols (i.e., CLSI M38-A2 and CLSI M51) designed for fungi. Hyphal plug, hyphal suspension, and zoospore are inocula commonly used in the drug susceptibility assessment for P. insidiosum. A side-by-side comparison demonstrated that each method had advantages and limitations. Minimum inhibitory and cidal concentrations of a drug varied depending on the selected method. Material availability, user experience, and organism and drug quantities determined which susceptibility assay should be used. We employed the hyphal plug and a combination of broth dilution and radial growth methods to screen and validate the anti-P. insidiosum activities of several previously reported chemicals, including potassium iodide, triamcinolone acetonide, dimethyl sulfoxide, and ethanol, in which data on their anti-P. insidiosum efficacy are limited. We tested each chemical against 29 genetically diverse isolates of P. insidiosum. These chemicals possessed direct antimicrobial effects on the growth of the pathogen in a dose- and time-dependent manner, suggesting their potential application in pythiosis treatment. Future attempts should focus on standardizing these drug susceptibility methods, such as determining susceptibility/resistant breakpoints, so healthcare workers can confidently interpret a result and select an effective drug against P. insidiosum.

Pythium insidiosum Keratitis: Past, Present, and Future

Pythium insidiosum (PI) is an oomycete, a protist belonging to the clade Stramenopila. PI causes vision-threatening keratitis closely mimicking fungal keratitis (FK), hence it is also labeled as "parafungus". PI keratitis was initially confined to Thailand, USA, China, and Australia, but with growing clinical awareness and improvement in diagnostic modalities, the last decade saw a massive upsurge in numbers with the majority of reports coming from India. In the early 1990s, pythiosis was classified as vascular, cutaneous, gastrointestinal, systemic, and ocular. Clinically, morphologically, and microbiologically, PI keratitis closely resembles severe FK and requires a high index of clinical suspicion for diagnosis. The clinical features such as reticular dot infiltrate, tentacular projections, peripheral thinning with guttering, and rapid limbal spread distinguish it from other microorganisms. Routine smearing with Gram and KOH stain reveals perpendicular septate/aseptate hyphae, which closely mimic fungi and make the diagnosis cumbersome. The definitive diagnosis is the presence of dull grey/brown refractile colonies along with zoospore formation upon culture by leaf induction method. However, culture is time-consuming, and currently polymerase chain reaction (PCR) method is the gold standard. The value of other diagnostic modalities such as confocal microscopy and immunohistopathological assays is limited due to cost, non-availability, and limited diagnostic accuracy. PI keratitis is a relatively rare disease without established treatment protocols. Because of its resemblance to fungus, it was earlier treated with antifungals but with an improved understanding of its cell wall structure and absence of ergosterol, this is no longer recommended. Currently, antibacterials have shown promising results. Therapeutic keratoplasty with good margin (1 mm) is mandated for non-resolving cases and corneal perforation. In this review, we have deliberated on the evolution of PI keratitis, covered all the recently available literature, described our current understanding of the diagnosis and treatment, and the potential future diagnostic and management options for PI keratitis.

Secretome Profiling by Proteogenomic Analysis Shows Species-Specific, Temperature-Dependent, and Putative Virulence Proteins of Pythium insidiosum

In contrast to most pathogenic oomycetes, which infect plants, Pythium insidiosum infects both humans and animals, causing a difficult-to-treat condition called pythiosis. Most patients undergo surgical removal of an affected organ, and advanced cases could be fetal. As a successful human/animal pathogen, P. insidiosum must tolerate body temperature and develop some strategies to survive and cause pathology within hosts. One of the general pathogen strategies is virulence factor secretion. Here, we used proteogenomic analysis to profile and validate the secretome of P. insidiosum, in which its genome contains 14,962 predicted proteins. Shotgun LC–MS/MS analysis of P. insidiosum proteins prepared from liquid cultures incubated at 25 and 37 °C mapped 2980 genome-predicted proteins, 9.4% of which had a predicted signal peptide. P. insidiosum might employ an alternative secretory pathway, as 90.6% of the validated secretory/extracellular proteins lacked the signal peptide. A comparison of 20 oomycete genomes showed 69 P. insidiosum–specific secretory/extracellular proteins, and these may be responsible for the host-specific infection. The differential expression analysis revealed 14 markedly upregulated proteins (particularly cyclophilin and elicitin) at body temperature which could contribute to pathogen fitness and thermotolerance. Our search through a microbial virulence database matched 518 secretory/extracellular proteins, such as urease and chaperones (including heat shock proteins), that might play roles in P. insidiosum virulence. In conclusion, the identification of the secretome promoted a better understanding of P. insidiosum biology and pathogenesis. Cyclophilin, elicitin, chaperone, and urease are top-listed secreted/extracellular proteins with putative pathogenicity properties. Such advances could lead to developing measures for the efficient detection and treatment of pythiosis.

A Review: Antimicrobial Therapy for Human Pythiosis

Human pythiosis is associated with poor prognosis with significant mortality caused by Pythium insidiosum. Antimicrobials’ in vitro and in vivo results against P. insidiosum are inconsistent. Although antimicrobials are clinically useful, they are not likely to achieve therapeutic success alone without surgery and immunotherapy. New therapeutic options are therefore needed. This non-exhaustive review discusses the rationale antimicrobial therapy, minimum inhibitory concentrations, and efficacy of antibacterial and antifungal agents against P. insidiosum. This review further provides insight into the immunomodulating effects of antimicrobials that can enhance the immune response to infections. Current data support using antimicrobial combination therapy for the pharmacotherapeutic management of human pythiosis. Also, the success or failure of antimicrobial treatment in human pythiosis might depend on the immunomodulatory effects of drugs. The repurposing of existing drugs is a safe strategy for anti-P. insidiosum drug discovery. To improve patient outcomes in pythiosis, we suggest further research and a deeper understanding of P. insidiosum virulence factors, host immune response, and host immune system modification by antimicrobials.

Global Distribution and Clinical Features of Pythiosis in Humans and Animals

Pythiosis is a difficult-to-treat infectious disease caused by Pythium insidiosum. The condition is unfamiliar among healthcare workers. Manifestation of pythiosis is similar to other fungal infections, leading to misdiagnosis and delayed treatment. The geographical extent of pythiosis at a global scale is unclear. This study aimed to analyze the clinical information recorded in the scientific literature to comprehensively project epidemiological characteristics, clinical features, and future trends of pythiosis. From 1980 to 2021, 4203 cases of pythiosis in humans (n = 771; 18.3%) and animals (primarily horse, dog, and cow; n = 3432; 81.7%), with an average of 103 cases/year, were recruited. Pythiosis case reports significantly increased in the last decade. Pythiosis spanned 23 tropical, subtropical, and temperate countries worldwide. Some patients acquired pythiosis from a trip to an endemic country. Strikingly, 94.3% of human cases were in India and Thailand, while 79.2% of affected animals were in the U.S.A. and Brazil. Clinical features of pythiosis varied. Vascular and ocular pythiosis were only observed in humans, whereas cutaneous/subcutaneous and gastrointestinal infections were predominant in animals. Mortality depended on host species and clinical forms: for example, none in patients with ocular pythiosis, 0.7% in cows with a cutaneous lesion, 26.8% in humans with vascular disease, 86.4% in dogs with gastrointestinal pathology, and 100% in several animals with disseminated infection. In summary, this study reports up-to-date epidemiological and clinical features of pythiosis in humans and animals. It increases awareness of this life-threatening disease, as the illness or outbreak can exist in any country, not limited to the endemic areas.