Precipitate production by some Malassezia species on Dixon's agar

An epidemiological study of animals dermatomycoses in Iran

OBJECTIVE

To determine the fungal species isolated from skin lesions of different animals suspected of having dermatomycoses and their prevalence in different regions of Iran.

MATERIALS AND METHODS

A total of 1011 animals (292 dogs, 229 cats, 168 horses, 100 camels, 98 cows, 60 squirrels, 37 birds, 15 sheep, 6 goats, 5 rabbits and 1 fox) suspected of having dermatomycoses were examined. The samples were obtained by plucking the hairs and feathers with forceps around the affected area and scraping the epidermal scales with a sterile scalpel blade. All collected samples were analyzed by direct microscopy and culture. Laboratory identification of the fungal isolates was based on their colonial, microscopic and biochemical characteristics.

RESULTS

Fungal agents were recovered from 553 (54.7%) animals suspected of having dermatomycoses. Of 553 confirmed cases, 255 (49.7%) were positive for dermatophytosis, 251 (45.4%) for Malassezia dermatitis, 14 (2.5%) for candidiasis, 12 (2.2%) for aspergillosis and 1 (0.2%) for zygomycosis. Cats (36.3%) were the most prevalent infected animals, followed by camels (13.4%), dogs (12.8%), horses (12.5%), cows (12.3%), squirrels (5.4%), birds (3.6%), sheep (2%), goats (1.1%), rabbits (0.4%) and fox (0.2%). Microsporum canis (M. canis) was the most frequent fungus isolated from dogs and fox, Malassezia pachydermatis (M. pachydermatis) from cats, horses and squirrels, Trichophyton verrucosum (T. verrucosum) from cows and camels, T. mentagrophytes var. mentagrophytes from sheep, goats and rabbits, and Aspergillus fumigatus (A. fumigatus) from birds.

CONCLUSION

The results suggested that periodic screening of animals suspected of having dermatomycoses and necessary treatments could help in the management of their public health problem.

Occurrence and distribution of Malassezia species on skin and external ear canal of horses

The aim of this study was to investigate the prevalence of Malassezia species from the body skin and external ear canal of healthy horses. The samples were obtained by scraping the skin surface from the nose, groin and dorsum and swabbing from the external ear canal of 163 animals, and then incubated on sabouraud dextrose agar and modified Dixon agar. Malassezia species were isolated from 34.9% of horses. The percentages of Malassezia species were 64.3% for Arab, 35.7% for Persian, 35.4% for Thoroughbred and 27.1% for Turkmen breeds. The greatest abundance of Malassezia species was found in the external ear canal (47.7%, representing significant difference with other sites), followed by nose (26.3%), groin (15.8%) and dorsum (10.5%) (P < 0.05). A total of 57 strains from six Malassezia species were detected with a frequency rate as follows: M. pachydermatis (33.3%), M. globosa (26.3%), M. sympodialis (14.1%), M. restricta (10.5%), M. obtusa (8.8%) and M. furfur (7%). The most common age-group affected was 1-3 years (59.4%). This study confirmed that cutaneous Malassezia microbiota in healthy horses varies by body site and age but not by breed and gender, representing M. pachydermatis as the most prevalent species on horse skin.

RAPD differentiation of Malassezia spp. from cattle, dogs and humans

The molecular characterization of Malassezia spp. isolates from animals and humans has not been thoroughly studied. We have analysed the DNA profile by random amplified polymorphic DNA (RAPD)-PCR to compare the genetic diversity between isolates from the external ears of cattle, dogs and humans. The analysis of electrophoretic profiles on 8% polyacrylamide gel and their phenograms showed genetic heterogeneity between RAPD profiles of Malassezia furfur and Malassezia slooffiae isolates from humans and cattle and between Malassezia pachydermatis isolates from dogs and cattle. Intra-species variations in DNA pattern of Malassezia isolates and the presence of specific genetic types in cattle, dogs or humans were observed. A review of genetic heterogeneity of these yeast in veterinary and human medicine studies is given considering a possible transmission animal to human or human to animal. Additional studies must clarify the differences between the RAPD band patterns observed in this and other studies, which would facilitate monitoring of Malassezia spp. carriage in domestic animals and in humans.

Revised culture-based system for identification of Malassezia species

Forty-six strains of Malassezia spp. with atypical biochemical features were isolated from 366 fresh clinical isolates from human subjects and dogs. Isolates obtained in this study included 2 (4.7%) lipid-dependent M. pachydermatis isolates; 1 (2.4%) precipitate-producing and 6 (14.6%) non-polyethoxylated castor oil (Cremophor EL)-assimilating M. furfur isolates; and 37 (34.3%) M. slooffiae isolates that were esculin hydrolyzing, 17 (15.7%) that were non-tolerant of growth at 40 degrees C, and 2 (1.9%) that assimilated polyethoxylated castor oil. Although their colony morphologies and sizes were characteristic on CHROMagar Malassezia medium (CHROM), all strains of M. furfur developed large pale pink and wrinkled colonies, and all strains of M. slooffiae developed small (<1 mm) pale pink colonies on CHROM. These atypical strains were distinguishable by the appearance of their colonies grown on CHROM. Three clinically important Malassezia species, M. globosa, M. restricta, and M. furfur, were correctly identified by their biochemical characteristics and colony morphologies. The results presented here indicate that our proposed identification system will be useful as a routine tool for the identification of clinically important Malassezia species in clinical laboratories.

Update on the genusMalassezia

Malassezia yeasts are commensals of normal human skin, but also cause pityriasis versicolor, seborrhoeic dermatitis and evidence is accumulating that they play a significant role in atopic eczema/dermatitis syndrome (AEDS; formerly atopic dermatitis). The taxonomy of the genus has changed considerably and is likely to change more in the future. Our understanding of the interaction between Malassezia and the host demonstrates that it has the paradoxical ability to both stimulate and suppress the immune response directed against it and there is a fine balance in its existence at the interface between commensalism and pathogenicity.

Tween 40-based precipitate production observed on modified chromogenic agar and development of biological identification kit for Malassezia species

We developed a simple identification kit for nine species of Malassezia (M. furfur, M. slooffiae, M. sympodialis, M. restricta, M. obtusa, M. globosa, M. pachydermatis, M. dermatis, and M. japonica) based on their biological features. This method utilizes Tween 40-based precipitate production on modified chromogenic agar (CHROMagar) Malassezia medium, growth on specific agars (Sabouraud's dextrose agar, Cremophor EL agar, Tween 60-esculin agar), and catalase reactions. This identification kit was verified with 11 type and reference strains of nine Malassezia species. An additional 26 clinical isolates were also successfully identified using the kit and the results were confirmed by molecular biological analysis.

The inhibition of Candida albicans by selected essential oils and their major components

Many volatile oils are known to possess antifungal properties and are potentially applicable as antimycotic agents. By studying the efficacy of essential oils against different pathogenic mycetes, we have evaluated the in-vitro inhibiting activity of some essential oils and their main constituents against a strain of Candida albicans. Sixteen commercial essential oils and forty-two pure constituents (alcohols, aldehydes, ketons, phenols and hydrocarbons), were tested by using a semisolid agar antifungal susceptibility (SAAS) method. Gas chromatography/mass spectroscopy analyses of the oils tested were performed. The essential oils of Origanum vulgare, Satureja montana, Mentha piperita, Cinnamomum verum, Cymbopogon flexuosus showed maximum inhibitory activity (MIC = 500 ppm) after 7 days. According to the results of the examination of pure constituents, beta-phellandrene proved to be the most interesting component among cyclic monoterpenic hydrocarbons as it showed a strong activity (MIC = 50 ppm). The most active of phenols was carvacrol (MIC 100 ppm). The open-chain alcohol 1-decanol was the most active of alcohols at 50 ppm. Finally, among aldehydes, a strong activity was shown by trans-cynnamaldehyde (MIC 50 ppm).

MfLIP1, a gene encoding an extracellular lipase of the lipid-dependent fungus Malassezia furfur

Malassezia furfur is a dimorphic fungus and a member of the normal cutaneous microflora of humans. However, it is also a facultative pathogen, associated with a wide range of skin diseases. One unusual feature of M. furfur is an absolute dependency on externally provided lipids which the fungus hydrolyses by lipolytic activity to release fatty acids necessary for both growth and pathogenicity. In this study, the cloning and characterization of the first gene encoding a secreted lipase of M. furfur possibly associated with this activity are reported. The gene, MfLIP1, shows high sequence similarity to other known extracellular lipases, but is not a member of a lipase gene family in M. furfur. MfLIP1 consists of 1464 bp, encoding a protein with a molecular mass of 54·3 kDa, a conserved lipase motif and an N-terminal signal peptide of 26 aa. By using a genomic library, two other genes were identified flanking MfLIP1, one of them encoding a putative secreted catalase, the other a putative amine oxidase. The cDNA of MfLIP1 was expressed in Pichia pastoris and the biochemical properties of the recombinant lipase were analysed. MfLip1 is most active at 40 °C and the pH optimum was found to be 5·8. The lipase hydrolysed lipids, such as Tweens, frequently used as the source of fatty acids in M. furfur media, and had minor esterase activity. Furthermore, the lipase is inhibited by different bivalent metal ions. This is the first molecular description of a secreted lipase from M. furfur.

Potential of plant oils as inhibitors of growth

Minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) were determined for 38 oils of plant origin against Candida albicans. Four strains including one standard strain were used in this study. The antifungal agents, Fluconazole and Amphotericin B were used as positive controls. The standard strain (ATCC10231) used in this study was found to be highly resistant to Fluconazole: 3000 microg ml(-1) of Fluconazole was required to inhibit the growth of this strain partially, and complete inhibition could not be achieved. Other Candida strains were sensitive to 5 microg ml(-1) of Fluconazole. All the strains used were sensitive to Amphotericin B. Of the 38 oils tested, 23 were found effective and fifteen were ineffective. Based on their MFCs, effective oils were categorized into three categories. Seven oils, which exerted fungicidal effect at less than 0.15% concentration of oils, were grouped into the most effective class. The oils exhibiting MFCs in the range of 0.16-1.5% concentration were considered moderately effective. Nine oils, which required more than 1.5% concentration, were regarded as less effective. The Fluconazole-resistant strain (MTCC 227) was sensitive to at least 23 of the plant oils. Results of this study indicate that oils of plant origin may find use as potential anti-Candida agents.

Prevalence of Malassezia spp. in healthy pigs

In the present study, we evaluated the occurrence of Malassezia spp. from superficial areas (ear, anus, forehead and back) in 100 healthy pigs. All cultures from anus, forehead and back were negative for Malassezia spp. A total of 73% of pigs were colonized by Malassezia yeasts in the external ear canals. We isolated only lipid-dependent species (Malassezia sympodialis 58%, Malassezia slooffiae 30%). This study evaluates the occurrence of Malassezia spp. in pigs since the taxonomic revision in 1996.

Malassezia nana sp. nov., a novel lipid-dependent yeast species isolated from animals

Five isolates of a novel species of the yeast genus Malassezia were isolated from animals in Japan and Brazil. Phylogenetic trees based on the D1/D2 domains of the large-subunit (26S) rDNA sequences and nucleotide sequences of the internal transcribed spacer 1 region showed that the isolates were conspecific and belonged to the genus Malassezia. They were related closely to Malassezia dermatis and Malassezia sympodialis, but were clearly distinct from these two species and the other six species of Malassezia that have been reported, indicating that they should be classified as a novel species, Malassezia nana sp. nov. Morphologically and physiologically, M. nana resembles M. dermatis and M. sympodialis, but can be distinguished from these species by its inability to use Cremophor EL (Sigma) as the sole lipid source and to hydrolyse aesculin. The type strain of M. nana is NUSV 1003(T) (=CBS 9557(T)=JCM 12085(T)).

The importance of microscopic examination in the management of desquamative diseases of the scalp

After determining the usual malassezic biota of the scalp in adult, normal persons, 259 patients with different desquamative diseases were studied by a simple adhesive tape technique. The main purpose of this study was to investigate the utility of this technique to improve the diagnosis and treatment of patients. Most patients with seborrhoeic dermatitis and sebopsoriasis demonstrated large numbers of Malassezia spp. cells corresponding to the so called "pityrosporosis". Only 43.6% of patients with pityriasis capitis (dandruff) presented with such a diagnosis. Symptomatic pityrosporosis of the scalp should be treated with imidazolic derivatives or other antifungal substances. Patients with psoriasis of the scalp showed a typical microscopic picture represented by parakeratosic (nucleated) keratinocytes with absence of lipophilic yeasts which should be attributed to the usual dryness of the scales Microbial epidermitis (eczema) of the scalp revealed another characteristic picture constituted by abundant leukocytes and bacteria without the presence of yeasts. The different microscopic pictures seen with this simple technique for diseases of the scalp, offer an adjunct to make a proper diagnosis and to establish a convenient treatment in cases which are not clinically well defined.

Identification of atypical strains of Malassezia spp. from cattle and dog

Yeast species in the genus Malassezia are lipophilic with the exception of Malassezia pachydermatis. During a study of the occurrence of Malassezia species in the external ear of 964 cattle and 6 dogs in Minas Gerais, Brazil, six lipid-dependent isolates could not be identified to known species. Four isolates came from healthy cows, one from a cow with otitis, and one from a healthy dog. When tested with Tweens and Cremophor EL as single sources of lipids, the strains grew on all sources except Cremophor EL. None of the six strains hydrolyzed esculin, and all produced catalase. Pigment production from tryptophan was variable. Partial large subunit rRNA sequences were obtained for two isolates that remained viable in culture. The strain from the cow with otitis was identified as a lipid-dependent variant of M. pachydermatis, and the strain from the dog was an atypical variant of Malassezia furfur.