Abstract
The aim of this study was to establish a ketoconazole susceptibility test for Malassezia pachydermatis using modified Leeming–Notman agar (mLNA). The susceptibilities of 33 M. pachydermatis isolates obtained by modified CLSI M27-A3 method were compared with the results by disk diffusion method, which used different concentrations of ketoconazole on 6 mm diameter paper disks. Results showed that 93.9% (31/33) of the minimum inhibitory concentration (MIC) values obtained from both methods were similar (consistent with two methods within 2 dilutions). M. pachydermatis BCRC 21676 and Candida parapsilosis ATCC 22019 were used to verify the results obtained from the disk diffusion and modified CLSI M27-A3 tests, and they were found to be consistent. Therefore, the current study concludes that this new novel test—using different concentrations of reagents on cartridge disks to detect MIC values against ketoconazole—can be a cost-effective, time-efficient, and less technically demanding alternative to existing methods.
Highlights
Malassezia spp. are zoonotic pathogens that cause atopy eczema in humans and otitis externa in dogs
A standard isolate of Candida parapsilosis ATCC 22019, which was kindly shared by Fungal Laboratory, Department of Biochemical Science and Technology, National Chiayi University, was used in this study to control the quality of the drug continuous dilution accuracy so that the skills of the technician and the quality of commercially available drugs could not affect the results of this experiment
The minimum inhibitory concentration (MIC) value of Candida parapsilosis ATCC 22019 against ketoconazole was the same as the value suggested by CLSI 2008 using the CLSI M27-A3 technique (0.5 μg/mL) [9]
Summary
Malassezia spp. are zoonotic pathogens that cause atopy eczema in humans and otitis externa in dogs. Malassezia pachydermatis is the most common strain [1]. To inhibit the infection of Malassezia spp., antifungal agents, such as nystatin, ketoconazole, and intraconazole, are often used. A survey conducted in a 2007 North American Veterinary Dermatology conference found that half of the attending veterinarians had encountered drug-resistant cases of yeast infection in canine otitis [2]. A 2011 report using Epsilometer test and modified M27-A2 methods mentioned that one strain of. M. pachydermatis showed a higher resistance against ketoconazole [3]. Some later reports have suggested that drug-resistant isolates might have emerged from Malassezia pachydermatis [4,5]
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