In vitro activity of carvacrol, cinnamaldehyde and thymol combined with antifungals against Malassezia pachydermatis

Malassezia pachydermatis is an important opportunistic agent of dermatitis and otitis in dogs. M. pachydermatis is generally treated with topical therapies using combinations of antifungal, antimicrobial and anti-inflammatory agents. We investigated the in vitro activities of carvacrol (CRV), cinnamaldehyde (CIN) and thymol (THY) alone and in combination with antifungal agents (fluconazole, itraconazole, ketoconazole, clotrimazole, miconazole, terbinafine and nystatin) against M. pachydermatis. The assays were performed according to the Clinical and Laboratory Standards Institute (CLSI), using Sabouraud dextrose broth and checkerboard microdilution. The mean fractional inhibitory concentration index (FICI) showed primary synergies for the combinations carvacrol+nystatin, thymol+nystatin, and carvacrol+miconazole (80%). In conclusion, the results obtained indicate that the phytochemicals tested showed relevant in vitro anti-M. pachydermatis activity. Future in vivo experiments are needed to elucidate the safety and therapeutic potential of these combinations.

An experimental murine model of otitis and dermatitis caused by Malassezia pachydermatis

We report a malasseziosis model in immunocompromised Swiss mice. For this model, the mice were immunosuppressed with a combination of cyclophosphamide at 150 mg/kg and hydrocortisone acetate at 250 mg/kg. Two groups were formed according to the site of inoculation. Dermatitis group received an intradermal injection of 5 × 10⁶ cell/mouse at a shaved dorsal region, while the otitis group received the same inoculum in the middle ear. Five animals/group were euthanised at different times, and the skin and ear were histopathologically analysed. During the first euthanasia, which occurred after inoculation, microscopic examination showed that all mice presented budding yeast-like in a tissue sample. The presence of yeasts decreased over time being undetected on the 17th day (dermatitis group) and the 21st day (otitis group) after inoculation. This is the first murine model for malasseziosis that can be useful for evaluating new treatment approaches.

Dendritic cells pulsed with Pythium insidiosum (1,3)(1,6)-β-glucan, Heat-inactivated zoospores and immunotherapy prime naïve T cells to Th1 differentiation in vitro

Pythiosis is a life-threatening disease caused by the fungus-like microorganism Pythium insidiosum that can lead to death if not treated. Since P. insidiosum has particular cell wall characteristics, pythiosis is difficult to treat, as it does not respond well to traditional antifungal drugs. In our study, we investigated a new immunotherapeutic approach with potential use in treatment and in the acquisition of immunity against pythiosis. Dendritic cells from both human and mouse, pulsed with P. insidiosum heat-inactivated zoospore, (1,3)(1,6)-β-glucan and the immunotherapeutic PitiumVac^® efficiently induced naïve T cell differentiation in a Th1 phenotype by the activation of specific Th1 cytokine production in vitro. Heat-inactivated zoospores showed the greatest Th1 response among the tested groups, with a significant increase in IL-6 and IFN-γ production in human cells. In mice cells, we also observed a Th17 pathway induction, with an increase on the IL-17A levels in lymphocytes cultured with β-glucan pulsed DCs. These results suggest a potential use of DCs pulsed with P. insidiosum antigens as a new therapeutic strategy in the treatment and acquisition of immunity against pythiosis.

Embryonated chicken eggs: An experimental model for Pythium insidiosum infection

Pythiosis is a severe disease caused by Pythium insidiosum. Currently, the research on the treatment of pythiosis uses rabbits as an experimental infection model. To reduce the use of animals in scientific experimentation, alternative models are increasingly necessary options. The objective of this study was to establish a new experimental infection model for pythiosis using embryonated chicken eggs. First, we tested the inoculation of 4 zoospore concentrations into the egg allantoic cavity at 3 embryonic days. We observed that increased zoospore concentration causes a decrease in survival time, and at a later embryonic day (the 14th) of infection, embryos showed delayed mortality. To confirm the reproducibility of the model, we chose the 14th embryonic day for the inoculation of 50 zoospores/egg, and the experiment was repeated twice. Mortality began with 30% embryos 48 hours after inoculation, and 95% embryos died within 72 hours. There was no mortality in the uninfected control group. The infection was confirmed by culture, PCR and histopathology. Immunohistochemistry confirmed the presence of hyphae in blood vessels in the umbilical cords in 95% of embryos and only 1 liver (5%). Our results suggest that embryonated eggs can be a very useful alternative infection model to study pythiosis.

Chemically induced disseminated pythiosis in BALB/c mice: A new experimental model for Pythium insidiosum infection

Pythiosis is a severe and life-threatening disease that affects humans and various animal species. We report a model of vascular/disseminated pythiosis occurring after subcutaneous inoculation of 2 x 10⁴Pythium insidiosum zoospores/mL in immunocompromised BALB/c mice. For this model, we carried out two rounds of experiments. First, we evaluated two protocols of immunosuppression before inoculation: cyclophosphamide at 150 mg/kg (CYP group) and cyclophosphamide 200 mg/kg plus hydrocortisone acetate at 250 mg/kg (CYP+HCA group). It was not possible to obtain mortality in the CYP group; however, the combination of CYP+HCA altered disease outcomes, with mortality rates reaching 60%. Second, we used the CYP+HCA immunosuppression protocol to analyze the histological and immunological statuses triggered by disease. When we inoculated immunocompetent mice with P. insidiosum zoospores, self-healing occurred via increased levels of IL-2, IFN-γ and IL-17A, which are characteristic of the Th1/Th17 cytokine response. For infected and immunosuppressed mice, the cytokine profiles showed high levels of IL-10, IL-6 and TNF-α. Increased IL-10 values are related to fungal infection susceptibility and led us to speculate that infection may be established through suppression of the host immune response. In addition, histopathological evaluation of the kidneys and liver demonstrated the presence of hyphae and the cellular findings suggested an acute vascular inflammation that mimics vascular/disseminated pythiosis in humans. This is the first murine model for pythiosis that is useful both for understanding the pathogenesis of this disease and for evaluating new treatment approaches.

Canine gastrointestinal pythiosis treatment by combined antifungal and immunotherapy and review of published studies

Pythium insidiosum is an oomycete, a fungal like microorganism, which infects mammals, causing pythiosis in animals and humans, especially in tropical and subtropical regions around the world. The treatment for this infection is very difficult, and therapeutic options commonly comprise surgery, immunotherapy and antimicrobial drugs. The present report describes the clinical healing of a dog with gastrointestinal pythiosis by treatment with a combination of antifungals and immunotherapy, as well as reviews the cases reported in the literature that used some type of therapy for canine pythiosis. A 2.5-year-old male beagle initially showed sporadic vomiting episodes, and this symptom became more frequent 5 months after the onset of clinical signs. Celiotomy procedure found thickness of the stomach wall extending to the pylorus and duodenum. A biopsy was performed, and the diagnosis of pythiosis was made by mycological, histopathological analyses and molecular identification. Therapy was based on an association of terbinafine plus itraconazole during 12 months and immunotherapy for 2.5 months. The healing of the dog reported here allows us to propose the use of immunotherapy associated with antifungal therapy to treat canine gastrointestinal pythiosis. However, additional studies should be performed on a larger number of patients to establish a standard treatment protocol for canine pythiosis.

Phylogenetic relationships of Brazilian isolates of Pythium insidiosum based on ITS rDNA and cytochrome oxidase II gene sequences

Pythium insidiosum is an aquatic oomycete that is the causative agent of pythiosis. Advances in molecular methods have enabled increased accuracy in the diagnosis of pythiosis, and in studies of the phylogenetic relationships of this oomycete. To evaluate the phylogenetic relationships among isolates of P. insidiosum from different regions of Brazil, and also regarding to other American and Thai isolates, in this study a total of thirty isolates of P. insidiosum from different regions of Brazil was used and had their ITS1, 5.8S rRNA and ITS2 rDNA (ITS) region and the partial sequence of cytochrome oxidase II (COX II) gene sequenced and analyzed. The outgroup consisted of six isolates of other Pythium species and one of Lagenidium giganteum. Phylogenetic analyses of ITS and COX II genes were conducted, both individually and in combination, using four different methods: Maximum parsimony (MP); Neighbor-joining (NJ); Maximum likelihood (ML); and Bayesian analysis (BA). Our data supported P. insidiosum as monophyletic in relation to the other Pythium species, and COX II showed that P. insidiosum appears to be subdivided into three major polytomous groups, whose arrangement provides the Thai isolates as paraphyletic in relation to the Brazilian ones. The molecular analyses performed in this study suggest an evolutionary proximity among all American isolates, including the Brazilian and the Central and North America isolates, which were grouped together in a single entirely polytomous clade. The COX II network results presented signals of a recent expansion for the American isolates, probably originated from an Asian invasion source. Here, COX II showed higher levels bias, although it was the source of higher levels of phylogenetic information when compared to ITS. Nevertheless, the two markers chosen for this study proved to be entirely congruent, at least with respect to phylogenetic relationships between different isolates of P. insidiosum.

Identification of Pythium insidiosum by nested PCR in cutaneous lesions of Brazilian horses and rabbits

Pythium insidiosum is a fungus-like organism present in subtropical and tropical areas, such as Brazil, known to infect humans and various animal species. P. insidiosum is the etiological agent of pythiosis, an emerging and granulomatous disease characterized mainly by cutaneous and subcutaneous lesions in horses, the principal species affected. Accurate diagnosis of pythiosis and identification of its causal agent by microbiological and serological tests can be often difficult and inconclusive principally for horses and humans. The aim of this study was to evaluate the application of the previously described P. insidiosum-specific nested polymerase chain reaction (PCR) assay to directly detect P. insidiosum DNA in clinical and experimental lesions. Universal fungal primers (ITS1 and ITS4) were used during the first-round of PCR to amplify ITS1, 5.8s, and ITS2. A second-round of PCR was conducted with P. insidiosum-specific primers (PI1 and PI2) to amplify a variable region within this ITS1. In this study, a total of 21 equine clinical samples (kunkers) and 28 specimens from experimentally infected rabbits were analyzed by nested PCR. The first-round of PCR generated 800-base pair products, and the second-round produced 105-base pair amplicons for each P. insidiosum-specific sample; no amplicons were generated in negative control samples. Our results suggest that nested PCR is an important and efficient tool for diagnosis of both endemic (horse samples) and experimental (rabbit samples) pythiosis.