Generation of protoplasts provides a powerful experimental research tool for biological and pathogenicity studies of Pythium insidiosum

INTRODUCTION

Pythiosis is a high-mortality infectious condition in humans and animals. The etiologic agent is Pythium insidiosum. Patients present with an ocular, vascular, cutaneous/subcutaneous, or gastrointestinal infection. Antifungal medication often fails to fight against P. insidiosum. The effective treatment is limited to radical surgery, resulting in organ loss. Fatal outcomes are observed in advanced cases. Pythiosis needs to be studied to discover novel methods for disease control. Genome data of P. insidiosum is publicly available. However, information on P. insidiosum biology and pathogenicity is still limited due to the lack of a cost-effective animal model and molecular tools.

MATERIALS AND METHODS

We aimed to develop a high-efficiency protocol for generating P. insidiosum protoplast, and used it to set up an animal model, in vitro drug susceptibility assay, and DNA transformation for this pathogen.

RESULTS

P. insidiosum protoplast was successfully generated to establish a feasible pythiosis model in embryonic chicken eggs and an efficient in vitro drug susceptibility assay. DNA transformation is a critical method for gene manipulation necessary for functional genetic studies in pathogens. Attempts to establish a DNA transformation method for P. insidiosum using protoplast were partly successful. Significant work needs to be done for genetically engineering a more robust selection marker to generate stable transformants at increased efficiency.

CONCLUSION

This study is the first to report an efficient P. insidiosum protoplast production for clinical and research applications. Such advances are crucial to speeding up the pathogen's biology and pathogenicity exploration.

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.

Identification and Biotyping of Pythium insidiosum Isolated from Urban and Rural Areas of Thailand by Multiplex PCR, DNA Barcode, and Proteomic Analyses

Pythium insidiosum causes pythiosis, a fatal infectious disease of humans and animals worldwide. Prompt diagnosis and treatment are essential to improve the clinical outcome of pythiosis. Diagnosis of P. insidiosum relies on immunological, molecular, and proteomic assays. The main treatment of pythiosis aims to surgically remove all affected tissue to prevent recurrent infection. Due to the marked increase in case reports, pythiosis has become a public health concern. Thailand is an endemic area of human pythiosis. To obtain a complete picture of how the pathogen circulates in the environment, we surveyed the presence of P. insidiosum in urban (Bangkok) and rural areas of Thailand. We employed the hair-baiting technique to screen for P. insidiosum in 500 water samples. Twenty-seven culture-positive samples were identified as P. insidiosum by multiplex PCR, multi-DNA barcode (rDNA, cox1, cox2), and mass spectrometric analyses. These environmental strains of P. insidiosum fell into Clade-II and -III genotypes and exhibited a close phylogenetic/proteomic relationship with Thai clinical strains. Biodiversity of the environmental strains also existed in a local habitat. In conclusion, P. insidiosum is widespread in Thailand. A better understanding of the ecological niche of P. insidiosum could lead to the effective prevention and control of this pathogen.

Identification, overexpression, purification, and biochemical characterization of a novel hyperthermostable keratinase from Geoglobus acetivorans

The goal of this study was to identify and biochemically characterize a novel hyperthermostable keratinase from microorganisms for feather waste degradation. Here, a hyperthermophilic Geoglobus acetivorans keratinase (GacK) gene was chosen based on a search of a sequence database. The selected GacK gene was synthesized, cloned, and successfully expressed without a signal peptide in the E. coli system. A monomer of approximately 58 kDa was obtained in a soluble form and purified. The recombinant GacK displayed the highest activity at an optimum temperature of 100 °C and a pH of 10. The hyperthermostable GacK enzymatic performance remained high even after incubation in nonionic surfactants and the chelating agent EDTA. The residual and keratinolytic activities of GacK, as determined with azocasein and keratin azure used as substrates, remained significantly greater than 80% at 130 °C for 7 h. The kinetic parameters Km and Vmax for azure keratin were 0.41 mg/ml and 875.14 unit/mg, respectively, while those for azocasein were 1.51 mg/ml and 505.32 unit/mg, respectively. The results suggest that the enzyme is among the most hyperthermostable keratinases. Because of its enzymatic characteristics to degrade keratin azure at high temperatures, GacK may potentially be utilized in future industrial applications.

An initial survey of 150 horses from Thailand for anti-Pythium insidiosum antibodies

INTRODUCTION

Pythium insidiosum causes a life-threatening infection termed pythiosis in humans and other animals. The organism has been identified in tropical and subtropical environments worldwide. Since 1985, human pythiosis has been increasingly reported from Thailand. Seroprevalence studies estimated that 32,000 Thai people had been exposed to the pathogen. In 2018, the first animal pythiosis case in Thailand was diagnosed in a horse. Here, we investigated the seroprevalence of anti-P. insidiosum antibodies in the Thai equine population.

MATERIALS AND METHODS

We surveyed serum anti-P. insidiosum antibodies in 150 horses distributed across Thailand, using three established serological tests: enzyme-linked immunosorbent assay (ELISA), immunochromatographic test (ICT), and Western blot analysis.

RESULTS

ELISA detected the anti-P. insidiosum antibodies in three horses. ICT and Western blot confirmed the presence of the antibodies in one of the ELISA-positive horses. Based on one positive out of 150 horses tested, the seroprevalence of anti-P. insidiosum antibodies in the Thai equine population was 0.7%, which is markedly higher than that in the Thai human population (0.07%), but much lower than that in the Brazilian equine population (11.1%).

CONCLUSION

The seroprevalence of the anti-P. insidiosum antibodies in the equine population suggests a higher incidence of pythiosis in horses than in humans. The antibody surveillance reported by our group was undertaken to promote a better understanding of the epidemiology and host susceptibility of pythiosis in Thailand.

Expression, purification, and characterization of the recombinant exo-1,3-β-glucanase (Exo1) of the pathogenic oomycete Pythium insidiosum

Pythiosis is a deadly infectious disease of humans and animals living in tropical and subtropical countries. The causative agent is the oomycete Pythium insidiosum. Treatment of pythiosis is challenging. The use of antimicrobial agents usually fails in the treatment of pythiosis. Many patients undergo surgical removal of an infected organ (i.e., eye, arm, and leg). The immunotherapeutic vaccine, prepared from the crude extract of P. insidiosum, shows limited efficacy against pythiosis. The fatal outcome occurs in patients with advanced disease. There are urgent needs for an effective therapeutic modality for pythiosis. Recently, the exo-1,3-β-glucanase (Exo1) has been identified as a conserve immunoreactive protein of P. insidiosum. Exo1 was predicted to reside at the cell membrane and hydrolyze cell wall β-glucan during cell growth. An Exo1 ortholog is absent in the human genome, making it an appealing target for drug or vaccine development. We attempted to clone and express the codon-optimized exo1 gene of P. insidiosum in E. coli. To solve the inclusion body formation, expression and purification of Exo1 were achievable in the denaturing condition using SDS- and urea-based buffers. Exo1 lacked hydrolytic activity due to the absence of proper protein folding and post-translational modifications. ELISA and Western blot analyses demonstrated the immunoreactivity of Exo1 against pythiosis sera. In conclusion, we successfully expressed and purified the immunoreactive Exo1 protein of P. insidiosum. The recombinant Exo1 can be produced at an unlimited amount and could serve as an extra protein to enhance the effectiveness of the current form of the vaccine against pythiosis.

Protein A/G-based enzyme-linked immunosorbent assay for detection of anti-Pythium insidiosum antibodies in human and animal subjects

Objectives

Pythiosis is a deadly infectious disease caused by Pythium insidiosum. Reports of both human and animal pythiosis are on the rise worldwide. Prognosis of the pythiosis patients relies on early diagnosis and prompt treatment. There are needs for an immunodiagnostic test that can detect the disease in both humans and animals. This study aims at reporting an optimized protocol for the development of a protein A/G-based enzyme-linked immunosorbent assay (ELISA) for the detection of anti-P. insidiosum antibody in multiple host species.

Results

A total of 25 pythiosis and 50 control sera, obtained from humans, horses, dogs, cats, and cows, were recruited for the assay development. With a proper ELISA cutoff point, all pythiosis sera can ultimately be distinguished from the control sera. The successfully-developed protein A/G-based ELISA can detect the anti-P. insidiosum antibodies in serum samples of both humans and animals. It is a versatile, feasible-to-develop, and functional immunodiagnostic assay for pythiosis.

Assessment of matrix-assisted laser desorption ionization-time of flight mass spectrometry for identification and biotyping of the pathogenic oomycete Pythium insidiosum

OBJECTIVE

Pythiosis is a life-threatening infectious disease caused by the oomycete Pythium insidiosum. The disease has been increasingly reported worldwide. Most patients with pythiosis undergo surgical removal of an infected organ. Early diagnosis contributes to better prognosis of pythiosis patients. Here, we assessed the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for identification and biotyping of P. insidiosum.

METHODS

A comprehensive set of mass spectra of P. insidiosum was generated to evaluate MALDI-TOF MS for identification and biotyping of P. insidiosum.

RESULTS

MALDI-TOF MS accurately identified all 13 P. insidiosum strains tested, at the species level. Mass spectra of P. insidiosum did not match any other microorganisms, including fungi (i.e., Aspergillus species, Fusarium species, and fungal species of the class Zygomycetes), which have similar microscopic morphologies with this oomycete. MALDI-TOF MS- and rDNA sequence-based biotyping methods consistently classified P. insidiosum into three groups: Clade-I (American strains), II (Asian and Australian strains), and III (mostly Thai strains).

CONCLUSIONS

MALDI-TOF MS has been successfully used for identification and biotyping of P. insidiosum. The obtained mass spectral database allows clinical microbiology laboratories, well-equipped with a MALDI-TOF mass spectrometer, to conveniently identify P. insidiosum, without requiring any pathogen-specific reagents (i.e., antigen, antibody or primers).

Biochemical and genetic analyses of the oomycete Pythium insidiosum provide new insights into clinical identification and urease-based evolution of metabolism-related traits

The oomycete microorganism, Pythium insidiosum, causes the life-threatening infectious condition, pythiosis, in humans and animals worldwide. Affected individuals typically endure surgical removal of the infected organ(s). Detection of P. insidiosum by the established microbiological, immunological, or molecular methods is not feasible in non-reference laboratories, resulting in delayed diagnosis. Biochemical assays have been used to characterize P. insidiosum, some of which could aid in the clinical identification of this organism. Although hydrolysis of maltose and sucrose has been proposed as the key biochemical feature useful in discriminating P. insidiosum from other oomycetes and fungi, this technique requires a more rigorous evaluation involving a wider selection of P. insidiosum strains. Here, we evaluated 10 routinely available biochemical assays for characterization of 26 P. insidiosum strains, isolated from different hosts and geographic origins. Initial assessment revealed diverse biochemical characteristics across the P. insidiosum strains tested. Failure to hydrolyze sugars is observed, especially in slow-growing strains. Because hydrolysis of maltose and sucrose varied among different strains, use of the biochemical assays for identification of P. insidiosum should be cautioned. The ability of P. insidiosum to hydrolyze urea is our focus, because this metabolic process relies on the enzyme urease, an important virulence factor of other pathogens. The ability to hydrolyze urea varied among P. insidiosum strains and was not associated with growth rates. Genome analyses demonstrated that urease- and urease accessory protein-encoding genes are present in both urea-hydrolyzing and non-urea-hydrolyzing strains of P. insidiosum. Urease genes are phylogenetically conserved in P. insidiosum and related oomycetes, while the presence of urease accessory protein-encoding genes is markedly diverse in these organisms. In summary, we dissected biochemical characteristics and drew new insights into clinical identification and urease-related evolution of P. insidiosum.

Probing the Phylogenomics and Putative Pathogenicity Genes of Pythium insidiosum by Oomycete Genome Analyses

Pythium insidiosum is a human-pathogenic oomycete. Many patients infected with it lose organs or die. Toward the goal of developing improved treatment options, we want to understand how Py. insidiosum has evolved to become a successful human pathogen. Our approach here involved the use of comparative genomic and other analyses to identify genes with possible functions in the pathogenicity of Py. insidiosum. We generated an Oomycete Gene Table and used it to explore the genome contents and phylogenomic relationships of Py. insidiosum and 19 other oomycetes. Initial sequence analyses showed that Py. insidiosum is closely related to Pythium species that are not pathogenic to humans. Our analyses also indicated that the organism harbours secreted and adhesin-like proteins, which are absent from related species. Putative virulence proteins were identified by comparison to a set of known virulence genes. Among them is the urease Ure1, which is absent from humans and thus a potential diagnostic and therapeutic target. We used mass spectrometric data to successfully validate the expression of 30% of 14,962 predicted proteins and identify 15 body temperature (37 °C)-dependent proteins of Py. insidiosum. This work begins to unravel the determinants of pathogenicity of Py. insidiosum.

Single nucleotide polymorphism-based multiplex PCR for identification and genotyping of the oomycete Pythium insidiosum from humans, animals and the environment

Pythium insidiosum causes a life-threatening infectious disease, called pythiosis, in humans and animals worldwide. Diagnosis of pythiosis is difficult and often delayed. Surgical removal of infected tissue is the main treatment option. Disabilities and death are common outcomes for pythiosis patients. Reports of Py. insidiosum infections are rising. While it would be useful for clinical, epidemiological, and microbiological studies, information on genetic variation in Py. insidiosum strains is limited. This limitation is, at least in part, due to the cost and time-requirements of DNA sequencing procedures. rDNA-sequence-based phylogenetic analyses categorize Py. insidiosum into three groups, in relation to geographic distribution: Clade-I (American strains), Clade-II (American, Asian, and Australian strains), and Clade-III (Thai and American strains). In rDNA sequence analyses, we observed single nucleotide polymorphisms (SNP) that were associated with the phylogenetic clades of Py. insidiosum. In this study, we aim to develop a multiplex PCR assay, targeting the identified SNPs, for rapid genotyping of Py. insidiosum. We also aim to assess diagnostic efficiency of the assay for identification of Py. insidiosum. Fifty-three isolates of Py. insidiosum from humans (n=35), animals (n=14), and the environment (n=4), and 22 negative-control fungi were recruited for assay evaluation. Based on the pattern of amplicons, the multiplex PCR correctly assigned phylogenetic clades in 98% of the Py. insidiosum isolates tested. The assay exhibited 100% sensitivity and specificity for identification of Py. insidiosum. The assay successfully identified and genotyped the first proven isolate of Py. insidiosum from an animal with pythiosis in Thailand. In conclusion, the multiplex PCR provided accurate, sensitive and specific results for identifying and genotyping Py. insidiosum. Thus, this multiplex-PCR assay could be a simple, rapid, and cost-effective alternative to DNA sequencing for the identification and genotyping of Py. insidiosum.

Protein A/G-based immunochromatographic test for serodiagnosis of pythiosis in human and animal subjects from Asia and Americas

Pythiosis is a life-threatening infectious disease of both humans and animals living in Asia, Americas, Africa, and parts of Australia and New Zealand. The etiologic pathogen is the fungus-like organism Pythium insidiosum The disease has high mortality and morbidity rates. Use of antifungal drugs are ineffective against P. insidiosum, leaving radical surgery the main treatment option. Prompt treatment leads to better prognosis of affected individuals, and could be achieved by early and accurate diagnosis. Since pythiosis has been increasingly reported worldwide, there is a need for a rapid, user-friendly, and efficient test that facilitates the diagnosis of the disease. This study aims to develop an immunochromatographic test (ICT), using the bacterial protein A/G, to detect anti-P. insidiosum IgGs in humans and animals, and compare its diagnostic performance with the established ELISA. Eighty-five serum samples from 28 patients, 24 dogs, 12 horses, 12 rabbits, and 9 cattle with pythiosis, and 143 serum samples from 80 human and 63 animal subjects in a healthy condition, with thalassemia, or with other fungal infections, were recruited for assay evaluation. Detection specificities of ELISA and ICT were 100.0%. While the detection sensitivity of ELISA was 98.8%, that of ICT was 90.6%. Most pythiosis sera, that were falsely read negative by ICT, were weakly positive by ELISA. In conclusion, a protein A/G-based ICT is a rapid, user-friendly, and efficient assay for serodiagnosis of pythiosis in humans and animals. Compared to ELISA, ICT has an equivalent detection specificity and a slightly lower detection sensitivity.

Efficiency comparison of three methods for extracting genomic DNA of the pathogenic oomycete Pythium insidiosum

BACKGROUND

The fungus-like organism Pythium insidiosum is the causative agent of a life-threatening tropical infectious disease, pythiosis, which has high rates of morbidity and mortality. A lack of reliable diagnostic tools and effective treatments for pythiosis presents a major challenge to healthcare professionals. Unfortunately, surgical removal of infected organs remains the default treatment for pythiosis. P. insidiosum is an understudied organism. In-depth study of the pathogen at the molecular level could lead to better means of infection control High quality genomic DNA (gDNA) is needed for molecular biology-based research and application development, such as: PCR-assisted diagnosis, population studies, phylogenetic analysis, and molecular genetics assays.

OBJECTIVE

To evaluate quality and quantity of the P. insidiosum gDNA extracted by three separate protocols intended for fungal gDNA preparation.

MATERIAL AND METHOD

Seven P. insidiosum isolates were subjected to gDNA extraction by using conventional-extraction, rapid-extraction, and salt-extraction protocols.

RESULTS

The conventional protocol offered the best gDNA in terms of quality and quantity, and could be scaled up. The rapid-extraction protocol had a short turnaround time, but the quality and quantity of the gDNA obtained were limited. The salt-extraction protocol was simple, rapid, and efficient, making it appealing for high throughput preparation of small-scale gDNA samples.

CONCLUSION

Compared to rapid-extraction protocol, both conventional-extraction and salt-extraction protocols provided a better quality and quantity of gDNA, suitable for molecular studies of P. insidiosum. In contrast to the other two methods, the salt-extraction protocol does not require the use of hazardous and expensive materials such as phenol, chloroform, or liquid nitrogen.