Quantification of Malassezia pachydermatis by real-time PCR in swabs from the external ear canal of dogs

Study of the variation of the Malassezia load in the interdigital fold of dogs with pododermatitis

The yeast Malassezia pachydermatis is a common inhabitant of the skin and mucosae of dogs. However, under certain circumstances this yeast can overgrow and act as an opportunistic pathogen causing otitis and dermatitis in dogs. Canine pododermatitis is a common disorder in dogs in which M. pachydermatis acts as an opportunistic pathogen. In the present study, the presence of Malassezia yeasts was assessed and quantified in samples collected from the interdigital space of dogs with pododermatitis before and after treatment, and from healthy dogs. The samples were subjected to two different cytological examinations, culture on Sabouraud glucose agar and modified Dixon's agar and a quantitative PCR targeting the internal transcribed spacer (ITS) genomic region. A selection of samples was analyzed by next generation sequencing (NGS) using the D1D2 domain of the large subunit of the ribosomal DNA as target. The pododermatitis samples before treatment showed higher cell counts, colony-forming units and ITS copies than the rest of samples. The NGS analysis revealed that Ascomycota was the main phylum in the healthy and post-treatment samples. However, Basidiomycota and M. pachydermatis was more abundant in the pododermatitis samples before treatment. These results support M. pachydermatis as an opportunistic agent in canine pododermatitis by a variety of methods, and demonstrate the correlation between cytologic and molecular methods for quantification.

Survey on the Presence of Malassezia spp. in Healthy Rabbit Ear Canals

Malassezia spp. have rarely been reported in rodents and lagomorphs. In 2011, Malassezia cuniculi was described in two rabbits. Further microscopic studies showed M. cuniculi-like yeasts in more than 50% of samples from rabbits’ ear canals, but no isolation was made. The present study details the presence of Malassezia spp. and tries to typify it from ear canals of healthy rabbits. Seventy-eight half-breed rabbits from rural farms and 98 companion dwarf rabbits from northern Italy were considered. A first attempt to screen ear swabs was performed by microscopic and cultural examination on Sabouraud Glucose Agar (SGA), modified Dixon Agar (mDA) and Leeming and Notman Agar (LNA). Additionally, ear swabs from eight further microscopically positive rabbits for M. cuniculi-like cells, were used for both isolation on LNA medium and nine of its variants and for DNA extraction, PCR and sequencing. The microscopic observation of the swabs of the screened 168 rabbits highlighted the presence of yeasts in one or both of the external ear canals of 98 rabbits (58.3%). Rabbits used for meat production were more frequently diagnosed positive than pet rabbits (P = 0.001), and young ones were more often positive compared to rabbits older than 3 months (P = 0.027). No yeast growth was observed in culture. From the eight selected rabbits, Malassezia isolation failed both on LNA and on the modified mediums. Sequences of ~300 bp fragments of 18s rDNA, obtained by PCR from swabs, showed 99.9% identity with Malassezia phylotype 131 described from human ear canals. As Malassezia-like yeasts have been observed in more than half of the examined population, its colonization of ear meatus can be considered as physiological in rabbits. The results outline how much remains to be discovered on Malassezia as a component of the skin mycobiota of rabbits and that the use of the culture examination alone is not the best choice to detect Malassezia-like yeasts in rabbits.

The canine skin and ear microbiome: A comprehensive survey of pathogens implicated in canine skin and ear infections using a novel next-generation-sequencing-based assay

This study analyzed the complex bacterial and fungal microbiota of healthy and clinically affected canine ear and skin samples. A total of 589 canine samples were included: 257 ear swab samples (128 healthy vs. 129 clinically affected) and 332 skin swab samples (172 healthy vs. 160 clinically affected) were analyzed using next-generation sequencing (NGS) to determine both relative and absolute abundances of bacteria and fungi present in the samples. This study highlighted the canine microbiota of clinically affected cases was characterized by an overall loss of microbial diversity, high microbial biomass, with overgrowth of certain members of the microbiota. The observed phenotype of these samples was best described by the combination of both relative and absolute microbial abundances. Compared to healthy samples, 78.3% of the clinically affected ear samples had microbial overgrowth; 69.8% bacterial overgrowth, 16.3% fungal overgrowth, and 7.0% had both bacterial and fungal overgrowth. The most important microbial taxa enriched in clinically affected ears were Malassezia pachydermatis, Staphylococcus pseudintermedius, Staphylococcus schleiferi, and a few anaerobic bacteria such as Finegoldia magna, Peptostreptococcus canis, and Porphyromonas cangingivalis. The anaerobic microbes identified here were previously not commonly recognized as pathogens in canine ear infections. Similar observations were found for skin samples, but yeasts and anaerobes were less abundant when compared to clinically affected cases. Results highlighted herein, signify the potential of NGS-based methods for the accurate quantification and identification of bacterial and fungal populations in diagnosing canine skin and ear infections, and highlight the limitations of traditional culture-based testing.

Malassezia Yeasts in Veterinary Dermatology: An Updated Overview

Lipophilic yeasts of the genus Malassezia are important skin commensals and opportunistic skin pathogens in a variety of animals. The species M. pachydermatis was first isolated from the skin of a captive Indian rhinoceros with an exfoliative dermatitis in 1925, recognized as an important otic pathogen of dogs in the 1950's, and finally accepted, after several years of controversy, as a common cause of canine dermatitis in the 1990's. Since then, there has been considerable research into the biology of Malassezia yeasts and their interaction with their animal hosts. In dogs and cats, M. pachydermatis is associated with ceruminous otitis externa and a "seborrhoeic" dermatitis, wherein pruritic, erythematous skin lesions, often with brown/black greasy, malodourous material matting hairs, preferentially develop in intertriginous areas. Skin disease is favored by folds, underlying hypersensitivity disorders, endocrinopathies, defects of cornification, and in cats, various visceral paraneoplastic syndromes. Diagnosis is based on detecting the yeast in compatible skin lesions, usually by cytology, and observing a clinical and mycological response to therapy. Treatment normally comprises topical or systemic azole therapy, often with miconazole-chlorhexidine shampoos or oral itraconazole or ketoconazole. Management of concurrent diseases is important to minimize relapses. Historically, wild-type Malassezia isolates from dogs and cats were typically susceptible to azoles, with the exception of fluconazole, but emerging azole resistance in field strains has recently been associated with either mutations or quadruplication of the ERG11 gene. These observations have prompted increased interest in alternative topical antifungal drugs, such as chlorhexidine, and various essential oils. Further clinical trials are awaited with interest.