Topical or oral azole antifungals are commonly used in canine atopic dermatitis (AD), as the lipophilic yeast Malassezia pachydermatis exacerbates canine AD. To examine whether canine AD lesions harbor azole-resistant M. pachydermatis isolates in East Asia, we investigated the in vitro susceptibility of M. pachydermatis isolates to ketoconazole (KTZ) and itraconazole (ITZ) obtained from AD lesions of canines in Japan, Korea and Taiwan. The minimum inhibitory concentrations (MICs) of KTZ and ITZ were measured by the E-test using Sabouraud dextrose agar with 0.5% Tween 40. The MICs of KTZ and ITZ for isolates from canines with AD were significantly higher than the MICs for isolates from healthy canines. Our findings suggested that the clinical isolates from canine AD skin lesions were less susceptible to azoles than those from normal canine skin in East Asia.

ABSTRACT. Isolates of the yeast Malassezia pachydermatis obtained from skin samples of healthy dogs and of dogs with atopic dermatitis in Japan, Taiwan and Korea were molecularly characterized using intergenic pacer 1 (IGS1) region analysis. The percentage of IGS1 subtype isolates detected in healthy skin was as follows: 1A (6%), 1B (27%), 1C (11%), 2A (6%), 2B (6%), 3A (11%), 3B (6%), 3C (3%) and 3D (24%). In contrast, the most prevalent isolates detected in skin lesions of atopic dermatitis were subtype 3D in Japan and Taiwan and subtype 3C in Korea. All subtype isolates grew well on acidic medium (pH 6). However, subtype 3C and 3D isolates grew better than the other subtype isolates on medium at pH 8. KEY The yeast Malassezia pachydermatis has been molecularly classified into three major groups (1, 2 and 3) with 10 subtypes (1A, 1B, 1C, 1D, 2A, 2B, 3A, 3B, 3C and 3D) for epidemiological studies [8]. In a previous study in Japan, subtype 3D isolates of M. pachydermatis were obtained more frequently from canine skin lesions of atopic dermatitis than from healthy canine skin. Moreover, the subtype 3D isolates grew much better on alkaline medium than the non-3D subtype isolates, indicating that the growth of specific subtypes of this yeast has a high dependence on the pH of the medium [3]. We hypothesized that subtype 3D isolates of M. pachydermatis would selectively grow on skin with a pH that was higher than normal. In particular, the pH of canine skin with activated apocrine secretion is reported to be more alkaline than that of healthy canine skin, with a pH ranging from 8.2 to 9.0 [4]. In addition, clinical signs of canine Malassezia dermatitis usually include alkaline waxy exudates, which enhance the growth of M. pachydermatis.In the present study, we investigated the characteristics of additional isolates of M. pachydermatis that were obtained from dogs in Japan, Taiwan and Korea in 2010 and 2011, in order to confirm the above-described pH-dependence of growth [3].M. pachydermatis isolates were obtained from 24 dogs without skin disease (all from Japan) and from 42 dogs with skin lesions of atopic dermatitis (11 from Japan, 11 from Korea and 20 from Taiwan). Atopic dermatitis was diagnosed according to Scott et al. [6] and Olivry et al. [5]. All patient dogs had typical lesions with greasy or waxy exudates. Samples were obtained from healthy skin (24 dogs) and from skin lesions of atopic dermatitis (42 dogs). Each sample was derived from at least 3 areas of the external ear, paw, and abdominal regions and samples were cultured using CHROMagar Malassezia medium (CHROMagarm, Paris, France) [2].Isolates of M. pachydermatis(n=182) were identified phenotypically based on morphology and on their ability to grow on medium with no lipid supplementation [1]. The isolates were divided into two groups: Group I consisted of 72 (3 strains per 1 dog) isolates collected from the healthy skin of 24 healthy dogs, and Group II consisted of 110 (2 or 3 isolates per 1 patient) isolates collected from the atopic dermatitis ...

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