Inhibitory Effects of Sulfonamide Derivatives on the β-Carbonic Anhydrase (MpaCA) from Malassezia pachydermatis, a Commensal, Pathogenic Fungus Present in Domestic Animals

Fungi are exposed to various environmental variables during their life cycle, including changes in CO₂ concentration. CO₂ has the potential to act as an activator of several cell signaling pathways. In fungi, the sensing of CO₂ triggers cell differentiation and the biosynthesis of proteins involved in the metabolism and pathogenicity of these microorganisms. The molecular machineries involved in CO₂ sensing constitute a promising target for the development of antifungals. Carbonic anhydrases (CAs, EC 4.2.1.1) are crucial enzymes in the CO₂ sensing systems of fungi, because they catalyze the reversible hydration of CO₂ to proton and HCO₃^-. Bicarbonate in turn boots a cascade of reactions triggering fungal pathogenicity and metabolism. Accordingly, CAs affect microorganism proliferation and may represent a potential therapeutic target against fungal infection. Here, the inhibition of the unique β-CA (MpaCA) encoded in the genome of Malassezia pachydermatis, a fungus with substantial relevance in veterinary and medical sciences, was investigated using a series of conventional CA inhibitors (CAIs), namely aromatic and heterocyclic sulfonamides. This study aimed to describe novel candidates that can kill this harmful fungus by inhibiting their CA, and thus lead to effective anti-dandruff and anti-seborrheic dermatitis agents. In this context, current antifungal compounds, such as the azoles and their derivatives, have been demonstrated to induce the selection of resistant fungal strains and lose therapeutic efficacy, which might be restored by the concomitant use of alternative compounds, such as the fungal CA inhibitors.

Epidemiological pattern of Malassezia, its phenotypic identification and antifungal susceptibility profile to azoles by broth microdilution method

Background

Malassezia though known for its cutaneous infections can potentially cause invasion. The skin infections caused by Malassezia have poor patient compliance due to its chronicity and recurrent nature of the disease. There is also a lack of standardised antifungal susceptibility profile for Malassezia due to its complex growth requirement.

Objective

This study was performed to understand the epidemiological pattern of disease and to study the antifungal susceptibility testing (AFST) profile so as to choose the appropriate drug/drugs to treat the infections caused by Malassezia.

Materials and Methods

Samples were collected and processed, species were identified by conventional method and AFST was done by broth microdilution method.

Results

The epidemiological pattern showed adolescent females commonly affected in torso. The most common lesion was pityriasis versicolor. The systemic antifungal of choice was itraconazole with the lowest minimum inhibitory concentration (MIC) of 0.125-1 μg/ml. The best topical drug with the lowest MIC value was clotrimazole 0.03-0.5 μg/ml.

Conclusion

AFST is important as it will help the dermatologist to choose the appropriate antifungal agents for the patient and thereby reduce the chronicity of the disease with good patient compliance.

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.

Characterization of the species Malassezia pachydermatis and re-evaluation of its lipid dependence using a synthetic agar medium

The genus Malassezia includes lipophilic yeasts, which are part of the skin microbiota of various mammals and birds. Unlike the rest of Malassezia species, M. pachydermatis is described as non-lipid-dependent, as it is able to grow on Sabouraud glucose agar (SGA) without lipid supplementation. In this study we have examined the phenotypic variability within M. pachydermatis and confirmed its lipid-dependent nature using a synthetic agar medium. We used a selection of representative non-lipid-dependent strains from different animal species and three atypical lipid-dependent strains of this species, which were not able to grow after multiple passages on SGA. More than 400 lipid-dependent Malassezia isolates from animals were studied in order to detect the three lipid-dependent strains of M. pachydermatis. The identity of the atypical strains was confirmed by DNA sequencing. On the other hand, we have modified the Tween diffusion test, which is widely used in the characterization of these yeasts, by using a synthetic agar-based medium instead of SGA. This modification has proved to be useful for differentiation of M. pachydermatis strains, providing reproducible results and a straightforward interpretation. The finding of these peculiar lipid-dependent strains exemplifies the large variability within the species M. pachydermatis, which involves rare atypical strains with particular growth requirements.

Frequency, Body Distribution, and Population Size of Malassezia Species in Healthy Dogs and in Dogs with Localized Cutaneous Lesions

Malassezia species are commensal organisms of human and animal skin that occasionally act as opportunistic pathogens. The lipid-dependent species are associated with human skin disorders, whereas the non–lipid-dependent species ( Malassezia pachydermatis) is considered as an opportunistic secondary pathogen affecting the canine skin surface and ear canal. This study evaluated the relationship between Malassezia yeasts, their population size, and the occurrence of skin lesions from healthy and skin-diseased dogs. The efficiency of cytological examination and fungal culture for Malassezia detection was also evaluated. From March 2002 to July 2003, 33 healthy dogs and 54 dogs with pruritic localized skin diseases were examined; skin swabs (1218) were collected from 7 anatomical sites for culture and cytological examination. Malassezia prevalence according to anatomical site and the agreement between cytological results and fungal cultures were statistically analyzed. Differences in mean colony forming unit counts between positive healthy and diseased dogs were evaluated using the Bonferroni test for post hoc pair-wise comparisons. In healthy dogs, Malassezia yeasts were most frequently isolated in the perianal and perioral areas. The frequency of isolation and population size of Malassezia species were higher in dogs with localized dermatitis, especially in affected areas, indicating a role for Malassezia in the occurrence of skin lesions. Malassezia pachydermatis was the species most commonly cultured from the skin and external ear canal of healthy and diseased dogs; isolation of lipid-dependent yeasts from healthy dogs was less frequent. Using fungal culture as the gold standard, cytological examination showed good relative specificity (95%) but very low relative sensitivity (30%).

Malassezia skin diseases in humans

Although Malassezia yeasts are a part of the normal microflora, under certain conditions they can cause superficial skin infection, such as pityriasis versicolor (PV) and Malassezia folliculitis. Moreover the yeasts of the genus Malassezia have been associated with seborrheic dermatitis and dandruff, atopic dermatitis, psoriasis, and, less commonly, with confluent and reticulated papillomatosis, onychomycosis, and transient acantholytic dermatosis. The study of the clinical role of Malassezia species has been surrounded by controversy due to the relative difficulty in isolation, cultivation, and identification. This review focuses on the clinical, mycologic, and immunologic aspects of the various skin diseases associated with Malassezia. Moreover, since there exists little information about the epidemiology and ecology of Malassezia species in the Italian population and the clinical significance of these species is not fully distinguished, we will report data about a study we carried out. The aim of our study was the isolation and the identification of Malassezia species in PV-affected skin and non-affected skin in patients with PV and in clinically healthy individuals without any Malassezia associated skin disease.

A comprehensive pathophysiology of dandruff and seborrheic dermatitis - towards a more precise definition of scalp health

Despite an increasing knowledge of dandruff and seborrheic dermatitis (D/SD), the pathophysiological understanding is still incomplete but suggests a role of Malassezia yeasts in triggering inflammatory and hyper-proliferative epidermal responses. The objective of this report is to review published literature from in vivo studies of D/SD populations to provide a more complete description of overall scalp health. New biomolecular capabilities establish a depth of pathophysiological understanding not previously achievable with traditional means of investigation. Biomarkers representing inflammation, hyper-proliferation and barrier function are all perturbed by the D/SD condition and robustly respond to therapeutic resolution. These biomarkers can be sampled noninvasively, enabling their use in routine clinical evaluations as either surrogate endpoints or complementary ones to classical signs/symptoms to broaden the etiological learning.

Could Malassezia yeasts be implicated in skin carcinogenesis through the production of aryl-hydrocarbon receptor ligands?

Malassezia yeasts are found on the skin of all humans and many warm-blooded animals. In vitro they have the ability to synthesize potent ligands (indolo[3,2-b]carbazole, malassezin and indirubin) of the aryl-hydrocarbon receptor (AhR; synonym: dioxin receptor) when the sweat contained L-tryptophan is used as the single nitrogen source. The production of these AhR-ligands has been associated with pathogenic strains of a certain Malassezia species (Malassezia furfur) but recent evidence shows that this property is widely distributed in almost all currently known Malassezia species. AhR is associated with carcinogenesis and the potential connection of these ubiquitous skin symbionts, and putative pathogens, with skin neoplasia should be evaluated mainly focusing on mechanisms related to the distinctive ability of the yeast to produce potent AhR ligands.

HYPOTHESIS

Synthesis of available pertinent data show a possible link between Malassezia produced AhR ligands and skin carcinogenesis, particularly of basal cell carcinoma (BCC). BCCs are almost exclusively observed in animal species colonized by Malassezia. In humans and animals there is overlapping in the skin regions colonized by this yeast and affected by BCC. The potent AhR ligands synthesized by pathogenic Malassezia strains could contribute to tumor promotion by: modification of the UV radiation carcinogenesis, alterations in the salvage/survival of initiated tumor cells, inhibition of cell senescence, interaction with vitamin D metabolism, promotion of immune tolerance and finally pro-carcinogenic modulation of cell cycle progression and apoptosis.

Pathogenesis of dermatophytosis and tinea versicolor

Dermatophytoses are infections caused by keratinophilic fungi known as dermatophytes. Several steps are required for infection to take place: contact, adherence, and invasion of keratin layers. The severity of the infection depends on the type of agent, environmental factors, and the host immunologic status. Tinea versicolor is caused by the Malassezia spp yeasts, which are microorganisms that belong to normal biota in seborrheic areas, but some contributing factors, such as the application of oily preparations, creams, an increase in ambient humidity, corticosteroid abuse, or genetic predisposition can induce its overgrowth in both filamentous and yeast structures. Exposure to sunlight stimulates the production of azelaic acid, which causes the appearance of hypopigmented spots. Currently, there is no scientific explanation for hyperpigmented lesions.

Malassezia species and seborrheic dermatitis

Malassezia spp. are medically important dimorphic, lipophilic yeasts that form part of the normal cutaneous microflora of human. Seborrheic dermatitis is a multifactor disease that needs endogenous and exogenous predisposing factors for its development. Presence of these factors leads to reproduction of the saprophytic opportunistic pathogen Malassezia spp. and development of a disease. The inflammatory reaction against the yeast Malassezia is considered basic in the etiology of the seborrheic dermatitis. The pathogenesis and exact mechanisms via which these yeasts cause inflammation are still not fully elucidated. They are rather complex and subject of controversy in literature. Most probably Malassezia spp. cause seborrheic dermatitis by involving and combining both nonummune and immune mechanisms (nonspecific and specific). Which of these mechanisms will dominate in any single case depends on the number and virulence of the yeasts as well as on the microorganism reactivity. In the recent years a great interest have been aroused by the epidemiological investigations. Depending on the geographical place of the countries different Malassezia species in seborrheic dermatitis dominate in the different countries. In view of the etiology and pathogenesis of the seborrheic dermatitis comprehensive antifungal preparations have been recently introduced and are nowadays the basic therapeutic resource in the treatment of this disease.

[Pityriasis versicolor and the yeasts of genus Malassezia]

Although pityriasis versicolor is the only human disease for which Malassezia yeasts have been fully established as pathogens, it is still not clear which species are implicated. Most studies carried out in recent years support our hypothesis - proposed in 1999 - that Malassezia globosa is the predominant species in pityriasis versicolor lesions, at least in temperate climates. Confirmation of this hypothesis could help us understand the conditions, as yet unclear, that induce transformation of this yeast from the saprophytic form present in healthy skin to the parasitic form, characterized by the formation of pseudomycelium, and could also guide therapy. In addition, isolation of another species, Malassezia furfur, which seems to be predominant in the tropics, raises the possibility of a second etiologic agent confined to certain areas, as occurs with some other human mycoses.

Skin diseases associated with Malassezia species in humans. Clinical features and diagnostic criteria

Malassezia yeasts not only cause the well known pityriasis versicolor and folliculitis, but also play an important role in other skin diseases, including seborrheic dermatitis and atopic dermatitis. The presence of Malassezia yeasts may be confirmed by direct microscopic examination and cultures of skin scrapings. In pityriasis versicolor the direct microscopic examination is the rapidest and surest test for confirming the clinical diagnosis. The preparation will show a cluster of globose budding spores with thick or double wall and short hyphae. For detecting Malassezia in the other diseases the cultures is preferable. Culture is useful both for confirming the clinical diagnosis and for epidemiological investigations. The identification of the Malassezia species is not easy. The microscopic observation of the colony direct towards the identification of Malassezia species, but it is not enough to identify the colonies definitely. Several biochemical tests are necessary for a precise identification, such as catalase reaction, growth on media without lipid sources, ability to utilize hydrophilic emulsifiers as sole lipid source, esculin test, tryptophan test.

The pathogenesis of Malassezia yeasts

The genus Malassezia includes twelve species of yeast, many of which have been mainly associated with human and canine diseases. Malassezia pachydermatis colonizes the skin and mucosal sites of healthy dogs and cats. Despite being part of the normal cutaneous microflora, Malassezia spp. yeast may become pathogenic under certain circumstances. This article reviews the factors related to both host and yeast which affect the pathogenical or commensal phenotypes of Malassezia yeasts.

Requirement for additional treatment for dogs with atopic dermatitis undergoing allergen-specific immunotherapy

Allergen-specific immunotherapy (ASIT) is one of the main treatments for atopic dermatitis in dogs, but it often requires additional treatments such as antibacterial and antifungal therapy for secondary bacterial and yeast infections, or antipruritic drugs to control the clinical signs or treat the adverse effects of the immunotherapy. Twenty-seven dogs enrolled in a study of ASIT were clinically assessed four times over a period of nine months; their requirement for treatment for secondary bacterial and yeast infections, for the administration of glucocorticoids as additional antipruritic therapy, and for the treatment of any adverse effects of the ASIT were evaluated. Twenty (74 per cent) of the dogs were treated for superficial bacterial pyoderma, 18 (66.6 per cent) required treatment for Malassezia species dermatitis on one or more occasions, eight (29.6 per cent) required treatment for otitis externa due to Malassezia species or bacteria, and eight required glucocorticoids to control their clinical signs. Five (18.5 per cent) of the dogs experienced adverse effects due to the ASIT and two required treatment with antihistamines (H1 receptor antagonists) in order to continue with the ASIT.

Isolation, characterization and molecular cloning of a lipolytic enzyme secreted from Malassezia pachydermatis

Lipophilic Malassezia species may induce catheter-associated sepsis in premature neonates and immunocompromised patients receiving parenteral lipid emulsions. To assess the participation of lipolytic enzymes in the pathogenesis of this yeast, we cloned a gene encoding the enzyme. A lipolytic enzyme in the culture supernatant of Malassezia pachydermatis was purified 210-fold to homogeneity. The enzyme showed high esterase activity toward p-nitrophenyl octanoate. The cDNA encoding the enzyme was cloned using a degenerate oligonucleotide primer constructed from the N-terminal amino acid sequence. The cDNA consisted of 1582 bp, including an open reading frame encoding 470 amino acids. The first 19 amino acids and the following 13 amino-acid sequence were predicted to be the signal peptides for secretion and prosequence, respectively. The predicted molecular mass of the 438-amino acid mature protein was 48 kDa. Analysis of the deduced amino acid sequence revealed that it contains the consensus motif (Gly-X-Ser-X-Gly), which is conserved among lipolytic enzymes. Homology investigations showed that the enzyme has similarities principally with 11 lipases produced by Candida albicans (29-34% identity) and some other yeast lipases.

Comparison of an antifungal agent with a mixture of antifungal, antibiotic and corticosteroid agents for the treatment of Malassezia species otitis in dogs

Twenty dogs with otitis externa in both ears and numerous Malassezia species yeasts on cytological examination were treated in one ear with a combination product containing clotrimazole, marbofloxacin and dexamethasone, and in the other ear with a topical antifungal containing miconazole. The effects of the treatments were analysed on the basis of the scores for pruritus, erythema and amount of cerumen, and the number of yeasts on cytological smears. There were reductions in the counts of Malassezia species after both treatments, but the combination product gave significantly greater reductions in erythema, cerumen and pruritus.

Antifungal activities of azole agents against the Malassezia species

In this paper, we identified 95 Malassezia isolates by morphological and biochemical criteria and assessed the in vitro activity of fluconazole, itraconazole, ketoconazole and voriconazole by broth microdilution against these species using slightly modified Leeming-Notman medium. The Malassezia isolates were identified as M. furfur (74), M. sympodialis (11), M. obtusa (8) and M. globosa (2). The modified Leeming-Notman medium used for susceptibility testing allowed good growth of Malassezia spp. Visual reading of the minimal inhibitory concentration (MIC) was readily achieved until Day 5 of incubation at 32 degrees C. Although high MIC values of 16 microg/mL for fluconazole were observed in 9.5% of Malassezia isolates, in general these microorganisms were susceptible to all drugs studied. Interestingly, one M. globosa isolate showed high MIC values for voriconazole, itraconazole and fluconazole. For the 95 strains, the MIC ranges were <0.03-4 microg/mL for ketoconazole, <0.03 to >16 microg/mL for voriconazole, <0.125 to >64 microg/mL for fluconazole and <0.03-16 microg/mL for itraconazole. In summary, the good reproducibility and visual readings obtained using modified Leeming-Notman medium suggest that this medium should be proposed for antifungal testing of drugs against Malassezia spp.

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.

Cytokine secretion profile of human keratinocytes exposed toMalasseziayeasts

The lipophilic yeast Malassezia is an exacerbating factor in atopic dermatitis (AD). Among organisms of the Malassezia species, Malassezia globosa and Malassezia restricta are particularly dominant on the skin of AD patients. However, the precise role of Malassezia yeasts in the pathophysiology of AD remains uncertain. Keratinocytes play a critical role in cutaneous inflammatory and immune responses by secreting cytokines. In this study, we attempted to determine the cytokine secretion profiles of human keratinocytes that were exposed to Malassezia yeasts. The human keratinocyte cell line PHK16-0b was cocultivated with M. globosa or M. restricta for 24 h, and the resulting cytokine secretion profile was analysed using a cytokine antibody array. The keratinocytes responded to the two Malassezia species with different Th2-type cytokine profiles, i.e. M. globosa induced IL-5, IL-10 and IL-13 secretion from the keratinocytes, whereas M. restricta induced IL-4 secretion. Similar results were obtained with primary normal human epidermal keratinocytes. cDNA microarray analysis confirmed that IL-5, IL-10, and IL-13 mRNAs were induced only by M. globosa, while IL-4 mRNA expression was induced only by M. restricta. These findings suggest that M. globosa and M. restricta play a synergistic role in triggering or exacerbating AD by stimulating the Th2 immune response.

Mycologic disorders of the skin

Cutaneous tissue can become infected when fungal organisms contaminate or colonize the epidermal surface or hair follicles. The skin can be a portal of entry for fungal infection when the epithelial barrier is breached or it can be a site for disseminated, systemic fungal disease. The two most common cutaneous fungal infections in small animals are dermatophytosis and Malassezia dermatitis. Dermatophytosis is a superficial cutaneous infection with one or more of the fungal species in the keratinophilic genera Microsporum, Trichophyton, or Epidermophyton. Malassezia pachydermatis is a nonlipid dependent fungal species that is a normal commensal inhabitant of the skin and external ear canal in dogs and cats. Malassezia pachydermatis is the most common cause of Malassezia dermatitis. The diagnosis and treatment of these cutaneous fungal infections will be discussed.

Malassezia yeasts and pityriasis versicolor

PURPOSE OF REVIEW

To analyze the relationships among different Malassezia species and pityriasis versicolor, the only human disease in which the etiologic role of these fungi is fully accepted (although the species implicated remains a matter of discussion).

RECENT FINDINGS

Since 1996, after the taxonomic revision of the genus, a limited number of papers analyzing the role of the different Malassezia species in pityriasis versicolor have been published or were the subject of presentations in congresses; there were only four in the past year. This paper discusses the results of these works, comparing them with results of the authors' most recent study in this field, conducted over the past 16 months.

SUMMARY

Most of the studies published thus far now show that Malassezia globosa is the predominant species found in the lesions of pityriasis versicolor, at least in temperate climates. The authors' recent findings confirm these results. The etiologic role of M. globosa in pityriasis versicolor is based, even more than on its isolation in a high percentage of cultures, on its identification by direct microscopy as typical globose yeast cells producing pseudohyphae in almost 100% of cases. The confirmation of the pathogenic role of this species in pityriasis versicolor could help in understanding these conditions, which are still unclear, which promote its transformation from the saprophytic stage present in healthy skin to the parasitic one, and could also help in selecting the best therapeutic measures.

[Malassezia related diseases]

The genus Malassezia is now divided into eleven species. Different species initiate or aggravate different skin diseases. In seborroheic dermatitis, M. restricta play an important role, while in atopic dermatitis, M. globosa and/or M. restricta are major cutaneous microflora. M. globosa is a causative species of tinea versicolor, and this species is also a causative species of malassezia folliculitis. We should therefore obtain better knowledge of the ecological and pathogenic roles of malassezia.

[Malassezia. Current knowledge and study perspectives]

The study of Malassezia has been postponed for many years due to its nutritional requirements and its morphological variability. Molecular biology methods led to a taxonomic revision of this genus and to a new interest for its clinical importance. Nowadays, 11 Malassezia species are known, 10 are lipophilic, having similar morphological, physiological and biochemical characteristics, therefore, conventional techniques are not useful to differentiating them. Molecular methods are an accurate tool in the identification and they lead to a better knowledge of the ecology and epidemiology of this genus. Noteworthy antifungal susceptibility variations have been observed in some species, although there is not a standard method for these yeasts. There are few data about their biochemical characteristics, and the enzymes they produce might be important virulence factors, favouring host tissue invasion. Malassezia has been recognised as a member of the normal human and animal skin. Its implication in pathologic processes, including skin diseases to systemic infections, is the main issue in current investigations in order to determine the real pathogenic role of these yeasts.

Canine serum immunoreactivity to M. pachydermatis in vitro is influenced by the phase of yeast growth

In western immunoblotting studies of canine sera using Malassezia pachydermatis extracts, the reported patterns of immunoreactivity vary between different laboratories. Because the duration of culture influences the antigenic composition of lipid-dependent Malassezia spp. when probed with human sera, we investigated whether the in vitro growth phase of M. pachydermatis influences immunoreactivity using canine sera. Extracts of M. pachydermatis CBS 1879 grown in Sabouraud's liquid medium at 37 degrees C for 2, 4, 6, 8 and 10 days were prepared by mechanical disruption, centrifugation, dialysis and lyophilization. Yeast growth phase was assessed by sequential colony counts and optical density measurements. Patterns of IgG immunoreactivity in high (n = 3) and low (n = 3) titre sera were compared using extracts prepared at each time point by sodium dodecyl sulphate polyacrylamide gel electrophoresis and western immunoblotting. Protein bands of 62 and 49 kDa were recognized by all sera, and 98 and 68 kDa bands were recognized by five sera. Proteins of 188, 66, 58, 57, 38, 28 and 17 kDa were only recognized by high titre sera. All high titre sera used recognized more bands in exponential phase (d2) extracts when compared with decline phase (d8-d10) extracts, and two of these sera showed most bands in stationary phase (d4-d6) extracts. Bands of 62 and 57 kDa were primarily detected in exponential and early stationary phase extracts. There is variation in antigenic expression in different growth phases of M. pachydermatis, which might explain discrepancies between previous laboratory studies of canine immunity to this yeast.

Fehlendes granulozytares Infiltrat bei der Pityriasis versicolor - ein Hinweis fur eine spezifische antiinflammatorische Aktivitat des Erregers? Missing granulocytic infiltrate in pityriasis versicolor - indication of specific anti-inflammatory activity of the pathogen?

The yeast Malassezia furfur is a part of the resident flora of human skin. It causes various diseases such as pityriasis versicolor, which hardly shows signs of inflammation despite marked clinical symptoms (e.g. hypopigmentation). The pathophysiology related morphological picture might give a clue to this phenomenon. As a part of the literature data are controversial, the present study compared the inflammatory infiltrate of pityriasis versicolor with that of tinea corporis in 40 human skin preparations each from diagnostic specimens. All preparations were stained with HE and PAS. Neutrophilic granulocytes were counted in the HE stain, and hyphae and spores in the PAS stain. The number of counted cells was related to the size of the respective area and the values were compared between pityriasis and tinea corporis. Significantly, more neutrophilic granulocytes were found with tinea corporis (P > 0.01), while they were virtually not demonstrable with pityriasis versicolor. It is surprising that fungal load in the stratum corneum is significantly higher with pityriasis versicolor (P > 0.01). Obviously the immune response involving neutrophilic granulocytes does not occur despite high bacterial load. This might be explained by reduced immunogenicity because of high content of lipids in the cell membrane. Furthermore, pityriarubins that are produced during tryptophan metabolism might be involved, which, in a stimulus-dependent manner, can suppress the ROS production of neutrophilic granulocytes in vivo.

Malassezia furfur in a case of onychomycosis: colonizer or etiologic agent?

The etiologic role of Malassezia furfur in onychomycosis is a contentious diagnostic problem because its keratinolytic ability has never been verified. This case report describes the isolation of M. furfur from the infected nails of a child clinically diagnosed with onychomycosis, and discusses the role of this organism as an etiologic agent/colonizer. The patient presented with subungual hyperkeratosis and onycholysis without associated paronychia. Budding yeast cells compatible with M. furfur were repeatedly demonstrated in KOH wet mounts of damaged nails, histopathology of hematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) stained sections showed penetration of fungal elements between deeper layers of keratin, and numerous colonies of M. furfur were isolated on three consecutive occasions from nail specimens collected from different areas of hand and toenail lesions. No evidence of nail invasion by dermatophytic or nondermatophytic filamentous fungi were found by direct microscopy or culture. Microscopy and culture were negative following 12 weeks of ketoconazole treatment, which resulted in growth of healthy nail plates with normal beds. We can infer from these observations that M.furfur was an etiologic agent rather than a colonizer in the patient's nails even though direct keratinolytic character of this fungus was not demonstrated.

Association between phospholipase production by Malassezia pachydermatis and skin lesions

An evaluation was made of the phospholipase activities of Malassezia pachydermatis strains isolated from healthy dogs versus those from dogs with dermatitis and otitis. A high percentage of strains of M. pachydermatis obtained from lesion sites (93.9%) produced phospholipase, compared to the strains obtained from healthy skin of the same dog with localized lesions (41.4%) and healthy dogs (10.6%).

Possible role of Malassezia furfur in psoriasis: modulation of TGF-beta1, integrin, and HSP70 expression in human keratinocytes and in the skin of psoriasis-affected patients

BACKGROUND

Psoriasis is a disease characterized by an abnormal pattern of keratinocyte growth and differentiation. Malassezia furfur forms part of the normal human skin flora. It may also be involved in the pathogenesis of psoriasis. To define the role of M. furfur in the pathogenesis of psoriasis, we investigated how M. furfur regulates molecules involved in cell migration and proliferation. The experiments were performed using human keratinocytes and skin biopsies from M. furfur-positive and -negative psoriasis-affected patients. In addition, we examined the signal transduction mechanisms involved.

MATERIALS AND METHODS

Western blot analysis was performed on human keratinocytes lysates treated or untreated with M. furfur and on biopsies from healthy and psoriasis patients. Signal transduction mechanisms involved were evaluated by electrophoretic mobility shift assay using the AP-1 inhibitor curcumin.

RESULTS

We found that M. furfur up-regulates transforming growth factor-beta1 (TGF-beta1), integrin chain, and HSP70 expression in human keratinocytes via AP-1-dependent mechanism. In the biopsies of M. furfur-positive psoriasis-affected patients, an increase in TGF-beta1, integrin chains, and HSP70 expression was found.

CONCLUSION

Our data suggest that M. furfur can induce the overproduction of molecules involved in cell migration and hyperproliferation, thereby favoring the exacerbation of psoriasis.

Assessment of the ability of Malassezia pachydermatis to stimulate proliferation of canine keratinocytes in vitro

OBJECTIVE

To investigate the direct interaction between canine keratinocytes and live Malassezia pachydermatis and thereby determine the role of these organisms in the pathogenesis of epidermal hyperplasia associated with Malassezia dermatitis in dogs.

SAMPLE POPULATION

Primary canine keratinocyte cultures established from skin samples obtained from clinically normal dogs.

PROCEDURE

The proliferative response of keratinocytes co-cultured with Malassezia organisms for 1, 2, or 3 days was assessed by use of direct manual counting (to determine the number of keratinocytes in both the monolayer and the medium) and immunohistochemical staining techniques involving antibodies against proliferating cell nuclear antigen (PCNA) and another cellular proliferation marker, Ki-67. The potential cytotoxic effect of Malassezia organisms was investigated by use of an apoptosis detection kit to label keratinocytes co-cultured with M. pachydermatis that underwent apoptosis.

RESULTS

No stimulatory effect of Malassezia organisms on canine keratinocyte proliferation was detected via cell counting and immunohistochemical techniques. However, there was a significant increase in dead keratinocytes in the medium with increasing numbers of Malassezia organisms in the co-culture. More apoptotic cells were observed in keratinocyte monolayers co-cultured with high numbers of M. pachydermatis than there were in monolayers cultured without Malassezia organisms, and the number increased after prolonged incubation.

CONCLUSIONS AND CLINICAL RELEVANCE

M. pachydermatis did not stimulate canine keratinocyte proliferation in vitro. The results suggested that the epidermal hyperplasia observed in dogs with Malassezia dermatitis is unlikely to be caused by a direct effect of the organism on the keratinocyte cell cycle, but is likely to involve other mechanisms.

Seborrheic dermatitis of the scalp: etiology and treatment

Seborrheic dermatitis is a common chronic infection of the lipid-rich areas of skin. While seborrheic dermatitis has been a recognized clinical entity for decades, its etiology is far from clear. Early investigators of the development of seborrheic dermatitis focused on the role of the Malassezia (previously Pityrosporum) yeasts. These yeasts are also normal skin commensals, thus their importance as pathogens in this disorder came to be doubted. However, it was subsequently found that treatment of seborrheic dermatitis with an antifungal agent not only resulted in clinical improvement but also reduced the number of Malassezia yeasts on the skin. This has resulted in a resurgence of interest in the Malassezia yeasts. It has been hypothesized that there is an immunological component to seborrheic dermatitis, possibly representing an abnormal host response to the Malassezia yeasts. This paper will discuss the role of Malassezia in the etiology of seborrheic dermatitis, as well as the various treatment options.

Cutaneous infections dermatophytosis, onychomycosis, and tinea versicolor

Cutaneous fungal infections cause significant morbidity for healthy and ill patients. The incidence of some dermatomycoses is increasing, despite availability of newer and better topical and systemic treatments. Fungal remnants last months to years under the ideal conditions, allowing continued spread of infection. Mycoses treated in one area may recur because of organism travel from concomitant areas of infection. Failure of patients and physicians to recognize a fungal etiology early may lead to more extensive, severe, or difficult-to-treat infections. Finally, a patient's concurrent illnesses may play a part in susceptibility and ability to manage fungal infections. For these reasons, scientists have studied and developed newer antifungal agents with better efficacy and greater convenience in dosing. These drugs, however, still have side effects and medication interactions that may limit their use in some patients. Better efforts to educate patients and physicians alike may aid in faster recognition and treatment of dermatophytoses. More research is needed to continue to develop drugs suitable for use in a broader range of patients and diagnostic tests that may be quicker or more specific than conventional ones.

Pathological and clinical aspects of the diseases caused by Malassezia species

From veterinary point of view Malassezia pachydermatis has the greatest significance. It has been standing in the focus of interest since the early 1990s, mostly because of the frequency of otitis externa and dermatitis caused by this yeast in dogs. This is the only lipid-independent species in the genus Malassezia. It can be found in very large proportion on the skin of healthy animals, but can be isolated in much greater number from diseased dogs. It often causes illness together with other pathogens (e.g. Staphylococcus intermedius). Some breeds are predisposed. In addition to the treatment of the accidental concurrent diseases, therapy consists of systemic and/or topical antimicrobial treatment. Ketoconazole is used most frequently. Malassezia pachydermatis plays also a role in the skin disorders of other carnivores. It has little zoonotic potential, it can be dangerous to immunocompromised humans. The other Malassezia species have little veterinary importance, although M. sympodialis and M. globosa were isolated from asymptomatic animals (mostly cats) and from mixed infections.

Failure of extracts from Malassezia pachydermatis to stimulate canine keratinocyte proliferation in vitro

Epidermal hyperplasia is one of the major histopathological features seen in dogs with Malassezia dermatitis. The aim of this study was to investigate the effects of extracts and culture supernatants from Malassezia pachydermatis on the proliferation of canine keratinocytes. Keratinocyte cultures were established from normal dog skin, and cell monolayers were co-cultured with Malassezia extracts (prepared either with or without protease inhibitors) and supernatants derived from organisms grown in liquid culture. The proliferation of keratinocytes was measured using a colourimetric assay. Neither the culture supernatants nor the Malassezia extracts had significant effects on the proliferation rate of canine keratinocytes, regardless of whether protease inhibitors were present or not. The results indicate that the epidermal hyperplasia seen in Malassezia dermatitis is unlikely to be caused directly by secretion of products from the organism.

Intradermal test reactivity to Malassezia pachydermatis in healthy basset hounds and basset hounds with Malassezia dermatitis

Nineteen healthy beagles, eight healthy basset hounds and 17 basset hounds with Malassezia dermatitis were tested intradermally with two extracts of M pachydermatis. One healthy beagle and two affected basset hounds showed wheal and flare reactions 15 minutes after the injection. Delayed reactions, consisting of erythematous macules and plaques, were commonly observed 24 hours after the injection in both the healthy and affected basset hounds, but occurred infrequently in the beagles. At 24 hours the diameters of the lesions in the healthy and affected basset hounds were significantly (P<0.01) greater than those in the healthy beagles, but the diameters in the healthy and affected basset hounds did not vary significantly. Delayed reactions in six of the basset hounds with Malassezia dermatitis were characterised histologically by superficial perivascular and periadnexal infiltrates of neutrophils and lymphocytes.

Immunoglobulin G responses to Malassezia pachydermatis in healthy dogs and dogs with Malassezia dermatitis

Serum immunoglobulin G (IgG) responses of healthy dogs and dogs with Malasseziapachydermatis dermatitis were compared by Western immunoblotting. M pachydermatis CBS 1879 was disrupted mechanically and its proteins were separated and blotted on to nitrocellulose membranes before being incubated with sera from eight healthy beagles, eight Irish setters with gluten-sensitive enteropathy, 15 healthy basset hounds, and 30 dogs with Mpachydermatis-associated dermatitis, 20 of which were basset hounds. The mean (se) numbers of bands of immunoreactivity observed in the seborrhoeic basset hounds (10.7 [0.4]) and affected mixed-breed dogs (9.4 [0.9]) were significantly greater than in the beagles (3-0 [1.0]), Irish setters (5.5 [1.1]) and healthy basset hounds (5.6 [0.7]). The number of bands identified was correlated (r(s) = 0.76, P < 0.001) with the anti-M pachydermatis IgG values measured by ELISA in a previous study. Most of the dogs were immunoreactive towards the 132, 66 and 50 to 54 kDa proteins and the affected dogs were also usually reactive towards the 219, 110, 71 and 42 kDa proteins.

Malassezia species in skin diseases

Since the taxonomic revision carried out in 1996, enlarging the genus Malassezia to comprise seven different species, a number of studies have investigated from different points of view -- mycological, molecular and immunological -- the relationships of these species with the pathologies associated with lipophilic yeasts, as well as its presence in healthy skin. From these studies, it now appears clear that Malassezia globosa is the main species associated with pityriasis versicolor, which is the only cutaneous disease in which the involvement of Malassezia is undisputed. Nevertheless, this species can also be found in normal skin, in which the predominant species is Malassezia sympodialis. In the remaining dermatological disorders related to Malassezia, the role of these yeasts is controversial. In seborrhoeic dermatitis, atopic dermatitis and folliculitis, several studies have focused on the immunological aspects that could explain the pathogenic mechanism. In other diseases, such as confluent and reticulate papillomatosis, neonatal pustulosis, otitis and onychomycosis, the presence or significance of Malassezia is still a matter of dispute.

Occurrence of Malassezia spp. in the external ear canals of dogs and cats with and without otitis externa

We studied the lipophilic microbiota of the external ear canals of 332 animals (264 dogs and 68 cats), with and without otitis externa, over an 11-year period from 1988 to 1999. Malassezia pachydermatis was isolated from 62.2% and 50% of dogs with and without otitis externa, respectively, and from 41.2% and 17.6% of cats with and without otitis externa, respectively. In the group of animals studied for lipid-dependent species, these yeasts were isolated from 4.5% of dogs with otitis externa and from 23.1% and 8.9% of cats with and without otitis externa, respectively. M. sympodialis and M. furfur were isolated from cats and M. furfur and M. obtusa from dogs. Our findings show that lipid-dependent Malassezia species may contribute to the etiology of otitis externa in dogs and cats.

Peripheral thromboembolism associated with Malassezia furfur sepsis

Malassezia furfur fungemia can cause sepsis in low birth weight neonates receiving parenteral lipids through central intravenous catheters. Its presentation has varied from nonspecific signs and symptoms to pulmonary vasculitis and endocarditis. We report the case of a premature infant who developed peripheral thromboembolic phenomena without evidence of endocarditis associated with M. furfur fungemia, an association not previously described.

Atopic eczema/dermatitis syndrome and Malassezia

Atopic dermatitis is a chronic multifactorial inflammatory skin disease, which has had a marked increase in prevalence during the last decades. Recently, a new nomenclature was recommended where the term 'atopic eczema/dermatitis syndrome' (AEDS) should be used to reflect the heterogeneity in this group of patients and where those patients without measurable IgE reactivity should be classified as either 'nonallergic AEDS' or 'non-IgE-associated allergic AEDS'. For nearly 20 years it has been discussed whether the opportunistic yeast Malassezia, previously designated Pityrosporum, is a contributing factor to AEDS. Today there are several reports that demonstrate specific serum IgE or positive skin prick test and/or atopy patch test reactions to Malassezia in patients with AEDS. Several IgE-binding components have been identified in extracts of Malassezia ranging in molecular mass between 10 and 100 kD. The genes for nine Malassezia allergens with molecular weights ranging from 14 to 36 kD have hitherto been identified and cloned. Six of them are now produced by recombinant techniques and used in diagnostic tests. At present the genus Malassezia is subdivided into seven different species, which all have been isolated from human skin. The respective contribution of different Malassezia spp. to AEDS and in what proportion they share allergens remains to be clarified. We summarize here data that Malassezia can play a role in eliciting and maintaining eczema in patients with AEDS.

[Current status and outlook of molecular identification and research on genus malassezia]

By molecular identification and typing, we have been able to analyze the pathogenicity and relationship between Malassezia-related diseases and species of this genus.

Immunology of diseases associated with Malassezia species

Malassezia species are members of the human cutaneous commensal flora, in addition to causing a wide range of cutaneous and systemic diseases in suitably predisposed individuals. Studies examining cellular and humoral immune responses specific to Malassezia species in patients with Malassezia-associated diseases and healthy controls have generally been unable to define significant differences in their immune response. The use of varied antigenic preparations and strains from different Malassezia classifications may partly be responsible for this, although these problems can now be overcome by using techniques based on recent work defining some important antigens and also a new taxonomy for the genus. The finding that the genus Malassezia is immunomodulatory is important in understanding its ability to cause disease. Stimulation of the reticuloendothelial system and activation of the complement cascade contrasts with its ability to suppress cytokine release and downregulate phagocytic uptake and killing. The lipid-rich layer around the yeast appears to be pivotal in this alteration of phenotype. Defining the nonspecific immune response to Malassezia species and the way in which the organisms modulate it may well be the key to understanding how Malassezia species can exist as both commensals and pathogens.

The ACVD task force on canine atopic dermatitis (XII): the relationship of cutaneous infections to the pathogenesis and clinical course of canine atopic dermatitis

Dogs and human beings with atopic dermatitis (AD) frequently exhibit concurrent skin infections with Staphylococcus sp. bacteria or Malassezia yeast, and treatment of such infections is an important facet of managing these patients. Staphylococci appear to colonize atopic skin readily, and bacterial products on the skin could augment cutaneous inflammation via immediate hypersensitivity responses to the bacteria, by superantigen-mediated lymphocyte activation, or other non-specific mechanisms. Similarly, skin colonization by Malassezia yeast could contribute to clinical signs of AD; yeast components could induce inflammation via non-specific mechanisms, such as alteration in mediator release, or via antigen-specific hypersensitivity reactions. Clinical and experimental evidence exists that secondary microbial infections can both initiate and perpetuate episodes of AD in dogs and humans, and could even participate in promotion of pro-allergic immunologic responses. Mechanistic details of these complex interactions are under extensive investigation in human beings; only a few observations have been extended to include dog with AD.

The lipophilic yeasts: state of the art and prospects

Malassezia yeasts (lipophilic yeasts), have been classified to include seven species. Although molecular methods such as sequencing of RNA and karyotyping were used to determine the species, traditional techniques are also being explored for their identification. These include studies of morphology and the utilization of individual lipids. Reports now show the predominance of individual species recovered from normal skin and from patients with diseases such as pityriasis versicolor and seborrhoeic dermatitis. The majority of systemic infections reported have been in the bloodstream of premature neonates. Clusters of cases have occurred and molecular techniques employed to study the epidemiology. With the development of discriminatory methods to determine individual species and strains present in disease and in nature, our understanding of the pathogenicity and the epidemiology of this genus can be advanced.

[Yeasts of the genus Malassezia: taxonomic classification and significance in (veterinary and) clinical medicine]

The historical development of the taxonomic classification of Malassezia yeasts until today yielded the description of seven different species based upon molecularbiological, morphological and biochemical parameters (M. furfur, M. pachydermatis, M. sympodialis, M. globosa, M. obtusa, M. restricta, M. slooffiae). Tests like Cremophor EL assimilation, esculin degradation, catalase test, pigment production and determination of polidocanol sensitivity appear to be suitable procedures for routine identification of the different species. Their colonization of clinically healthy humans (in particular M. sympodialis, M. globosa, M. obtusa) and animals (M. pachydermatis) skin renders interpretation difficulties, when isolating Malassezia spp. from clinical specimens. Out of the seven species, in man the clinical significance of M. furfur for pityriasis versicolor and systemic infections appears to be accepted largely. In dogs and cats M. pachydermatis has been regarded as cause of otitis externa and seborrhoeic dermatitis. But, due to geno- and phenotypic variabilities described for M. pachydermatis field isolates further investigations concerning the taxonomic uniformity of the species are necessary.