Pramote Vanittanakom

Rhizomys sumatrensis and Cannomys badius, new natural animal hosts of Penicillium marneffei

The incidence of Penicillium marneffei infection has increased substantially, especially in persons with HIV infection. Very little is known about the natural reservoirs or animal hosts of P. marneffei. This pathogenic fungus was first isolated from a species of bamboo rat (Rhizomys sinensis) in Vietnam and later from another rodent species, R. pruinosus. We studied a total of 75 captured bamboo rats; P. marneffei could be isolated from the internal organs of 13 of 14 (92.8%) of large bamboo rats, R. sumatrensis, and of 3 of 10 reddish-brown small bay bamboo rats, Cannomys badius (30%). All 51 greyish-black C. badius were negative on culture. Among R. sumatrensis, P. marneffei were frequently recovered from the lungs (85.7%), spleen (50%) and liver (28.6%). Of the 28 soil samples collected from the bamboo rat burrows and the 67 from the residential areas of patients with P. marneffei infection, P. marneffei was isolated from one soil sample collected from a burrow of R. sumatrensis. The mycological characteristics of P. marneffei isolates from bamboo rats and humans were very similar. Our data indicate that R. sumatrensis and C. badius may be important animal hosts of P. marneffei in northern Thailand.

Rapid Identification of Penicillium marneffei by PCR-Based Detection of Specific Sequences on the rRNA Gene

ABSTRACT An emerging pathogenic dimorphic fungus, Penicillium marneffei, is one of the major causes of morbidity in patients with human immunodeficiency virus infection in Southeast Asia. A PCR-hybridization assay has been developed to identify this pathogen. This study describes the use of single and nested PCR methods for the rapid identification of P. marneffei. Two sets of oligonucleotide primers were derived from the sequence of 18S rRNA genes of P. marneffei. The outer primers (RRF1 and RRH1) were fungus specific. The inner primers (Pm1 and Pm2) were specific for P. marneffei and were used in nested or single PCR. The specific fragment of approximately 400-bp was amplified from both mold and yeast forms of 13 P. marneffei human isolates, 12 bamboo rat isolates, and 1 soil isolate, but not from other fungi, bacteria, and human DNA. The amplified products were analyzed by agarose gel electrophoresis followed by ethidium bromide staining. The sensitivities of the single PCR and nested PCR were 1.0 pg/μl and 1.8 fg/μl, respectively. The assay is useful for rapid identification of P. marneffei cultures. Very young culture of P. marneffei (2-day-old filamentous colony, 2 mm in diameter) could be performed by this assay. The species was identified within 7 h (single PCR) or 10 h (nested PCR), compared to 4 to 7 days for confirmation of dimorphism. The application of these PCR methods for early diagnosis of the disease needs to be studied further.

The Copper, Zinc Superoxide Dismutase Gene of Penicillium marneffei: Cloning, Characterization, and Differential Expression During Phase Transition and Macrophage Infection

Superoxide dismutase (SOD) is an enzyme that converts superoxide radicals into hydrogen peroxide and oxygen molecules. SOD has been shown to contribute to the virulence of many human-pathogenic fungi through its ability to neutralize toxic levels of reactive oxygen species generated by the host. SOD has also been speculated to be important in the pathogenesis of fungal infections, but the role of this enzyme has not been rigorously investigated. In this report, we isolated and characterized the copper, zinc superoxide dismutase gene, designated sodA, from the important human pathogenic fungus, Penicillium marneffei. The putative SodA polypeptide consisted of 154 amino acids and exhibited a significant level of similarity to other fungal Cu, Zn SODs. Differential expression of the sodA gene in P. marneffei was demonstrated by semi-quantitative RT-PCR. Apparently, the sodA transcript accumulated in conidia, but expression was downregulated in the mycelia phase. In contrast, transcript expression was upregulated in the yeast phase as well as during macrophage infection. The significantly higher expression of the sodA transcript during macrophage infection suggests that this gene might play an important role in stress responses and in the adaptation of P. marneffei to the internal macrophage environment. The latter may serve as a putative virulence factor of this fungus allowing for survival in the host cell.

Rapp-Hodgkin syndrome with palmoplantar keratoderma, glossy tongue, congenital absence of lingual frenum and of sublingual caruncles: Newly recognized findings

We report on a boy with Rapp-Hodgkin syndrome (RHS) or Rapp-Hodgkin ectodermal dysplasia. He had sparse, wiry, slow growing and uncombable hair, but no pili torti or pili canaliculi characteristic of RHS. He also had sparse eyelashes and eyebrows, and obstructed lacrimal puncta and epiphora. Bilateral bony external auditory canal stenosis led to hearing loss. The mouth was small with repaired bilateral cleft lip and palate. Oral manifestations included hypodontia, microdontia, unerupted mandibular premolars with well formed roots, large dental pulp spaces, enamel hypoplasia, multiple caries, glossy tongue, and congenital absence of lingual frenum and of sublingual caruncles including submandibular and sublingual salivary duct openings. Palmo-plantar keratoderma, unerupted premolars, congenital absence of lingual frenum, sublingual caruncles, glossy tongue, and pili canaliculi seen in the patient are newly recognized findings of this syndrome. Overlapping findings of RHS ectrodactyly-ectodermal dysplasia-clefting syndrome (EEC), and ankyloblepharon-ectodermal defects-cleft lip and palate syndrome (AEC) are discussed.

Efficiency of the flotation method in the isolation of Penicillium marneffei from seeded soil

The efficiency of a modified flotation method for the isolation of Penicillium marneffei from soils has been evaluated. About 80% was recovered from sterilized soil freshly seeded with P. marneffei (100 conidia/1.5 g soil). When seeded non-sterile soil was used (at least 100 seeded conidia/1.5 g soil), P. marneffei could be effectively recovered by employing a combination of the flotation method and the mouse inoculation method.

Functional Analysis of atfA Gene to Stress Response in Pathogenic Thermal Dimorphic Fungus Penicillium marneffei

Penicillium marneffei, the pathogenic thermal dimorphic fungus is a causative agent of a fatal systemic disease, penicilliosis marneffei, in immunocompromised patients especially HIV patients. For growth and survival, this fungus has to adapt to environmental stresses outside and inside host cells and this adaptation requires stress signaling pathways and regulation of gene expression under various kinds of stresses. In this report, P. marneffei activating transcription factor (atfA) gene encoding bZip-type transcription factor was characterized. To determine functions of this gene, atfA isogenic mutant strain was constructed using the modified split marker recombination method. The phenotypes and susceptibility to varieties of stresses including osmotic, oxidative, heat, UV, cell wall and cell membrane stresses of the mutant strain were compared with the wild type and the atfA complemented strains. Results demonstrated that the mRNA expression level of P. marneffei atfA gene increased under heat stress at 42°C. The atfA mutant was more sensitive to sodium dodecyl sulphate, amphotericin B and tert-butyl hydroperoxide than the wild type and complemented strains but not hydrogen peroxide, menadione, NaCl, sorbitol, calcofluor white, itraconazole, UV stresses and heat stress at 39°C. In addition, recovery of atfA mutant conidia after mouse and human macrophage infections was significantly decreased compared to those of wild type and complemented strains. These results indicated that the atfA gene was required by P. marneffei under specific stress conditions and might be necessary for fighting against host immune cells during the initiation of infection.

Molecular detection of Pythium insidiosum from soil in Thai agricultural areas

Pythium insidiosum is an aquatic fungus-like organism in the kingdom Stramenopila that causes pythiosis in both humans and animals. Human pythiosis occurs in ocular, localized granulomatous subcutaneous and systemic or vascular forms. Individuals whose occupations involve exposure to aquatic habitats have an elevated risk of contracting pythiosis. Previously, we reported the first successful isolation of Pythium insidiosum from aquatic environmental samples by culture including confirmation using molecular methods. In this study, we show that P. insidiosum inhabitats moist soil environments in agricultural areas. A total of 303 soil samples were collected from 25 irrigation sources in the areas nearby the recorded home addresses of pythiosis patients residing in northern provinces of Thailand. P. insidiosum DNA was identified directly from each soil extract by using a nested PCR assay and subsequent phylogenetic analysis of the ribosomal intragenic spacer region. P. insidiosum DNA could be detected from 16 of the 25 soil sources (64%). Conventional culture methods were also performed, however all samples exhibited negative culture results. We conclude that both irrigation water and soil are the natural reservoirs of P. insidiosum. In endemic areas, the exposure to these environmental reservoirs should be considered a risk factor for hosts susceptible to pythiosis.

Haplorchis taichui: Worm recovery rate and immune responses in infected rats (Rattus norvegicus)

Worm recovery rate, mucosal mast cells (MMCs), eosinophils and serum IgE concentration in rats were investigated after orally feeding 300 Haplorchis taichui metacercariae to male rats. The duodenal, jejunal and ileal tissue sections were stained with 1% alcian blue and 0.5% safranin-O for MMC count. Eosinophil count and the serum IgE concentration assay were measured from cardiac puncture blood. The average worm recovery rates were 20.00%, 13.00%, 0.67%, 1.67% and 0.00% on day 3, 7, 14, 21 and 28 post-infection (PI), respectively. The number of MMCs in the infected rats were significantly higher than in the controls (P<0.01), reaching a peak on day 21 PI. They decreased thereafter, with the decline in worm recovery. Eosinophil count and Serum IgE concentration were also increased but not significantly higher than the controls. However, they showed a positive relationship to worm recovery. It could be concluded from the results that MMCs, eosinophils and IgE may play an important role in the expulsion of H. taichui from rat intestine. However, the mechanism by which the MMC result in the helminth expulsion still need to be understood, and it is recommended that other cells such as goblet cells be studied further.

Role of the rttA gene in morphogenesis, stress response, and virulence in the human pathogenic fungus Penicillium marneffei

Penicillium marneffei is a human pathogenic fungus and the only thermally dimorphic species of the genus. At 25°C, P. marneffei grows as a mycelium that produces conidia in chains. However, when incubated at 37°C or following infection of host tissue, the fungus develops as a fission yeast. Previously, a mutant (strain I133) defective in morphogenesis was generated via Agrobacterium-mediated transformation. Specifically, the rtt109 gene (subsequently designated rttA) in this mutant was interrupted by T-DNA insertion. We characterized strain I133 and the possible roles of the mutated rttA gene in altered P. marneffei phenotypes. At 25°C, the rttA mutant produces fewer conidia than the wild type and a complemented mutant strain, as well as slower rates of conidial germination; however, strain I133 continued to grow as a yeast in 37°C-incubated cultures. Furthermore, whereas the wild type exhibited increased expression of rttA at 37°C in response to the DNA-damaging agent methyl methane sulfonate, strain I133 was hypersensitive to this and other genotoxic agents. Under similar conditions, the rttA mutant exhibited decreased expression of genes associated with carbohydrate metabolism and oxidative stress. Importantly, when compared with the wild-type and the complemented strain, I133 was significantly less virulent in a Galleria infection model when the larvae were incubated at 37°C. Moreover, the mutant exhibited inappropriate phase transition in vivo. In conclusion, the rttA gene plays important roles in morphogenesis, carbohydrate metabolism, stress response, and pathogenesis in P. marneffei, suggesting that this gene may be a potential target for the development of antifungal compounds.

Role of the Talaromyces marneffei (Penicillium marneffei) sakA gene in nitrosative stress response, conidiation and red pigment production

Abstract Stress‐activated MAPK pathways are systems used to regulate the stress adaptation of most fungi. It has been shown that in Talaromyces marneffei (Penicillium marneffei), a pathogenic dimorphic fungus, the sakA gene is involved, not only in tolerance against oxidative and heat stresses, but also in playing a role in asexual development, yeast cell generation in vitro and survival inside macrophage cell lines. In this study, the role of the T. marneffei sakA gene on the nitrosative stress response and the regulation of gene expression were investigated. The susceptibility of the sakA mutant to NaNO2 was investigated using drop dilution assay and the expression of genes of interest were determined by RT‐PCR, comparing them to the wild‐type and complemented strains. The results demonstrated that the T. marneffei sakA gene played a role in the stress response to NaNO2, the expression of genes functioning in conidial development (brlA, abaA and wetA) and red pigment biosynthesis (pks3, rp1, rp2 and rp3). These findings suggest that T. marneffei sakA is broadly involved in a wide variety of cell activities, including stress response, cell morphogenesis, asexual development and pigmentation.