Biofilm formation in Malassezia pachydermatis strains isolated from dogs decreases susceptibility to ketoconazole and itraconazole

Jerzsele, Ákos and Gyetvai, Béla and Csere, István and Gálfi, Péter (2014) Biofilm formation in Malassezia pachydermatis strains isolated from dogs decreases susceptibility to ketoconazole and itraconazole. Acta Veterinaria Hungarica, 62 (4). pp. 473-480. ISSN 0236-6290

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Abstract

Malassezia pachydermatis is a commonly isolated yeast in veterinary dermatology that can produce biofilms in vitro and in vivo, lowering its susceptibility to antimicrobial drugs. The aim of this study was to determine and compare the in vitro susceptibility of planktonic cells and biofilms of M. pachydermatis isolates to ketoconazole and itraconazole. The presence of biofilm formation was confirmed by crystal violet staining and absorbance measurement at 595 nm wavelength, and by a scanning electron microscopy method. Cell viability was determined by the Celltiter 96 Aqueous One solution assay containing a water-soluble tetrazolium compound (MTS) with absorbance measurement at 490 nm. Planktonic cell minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) of ketoconazole and itraconazole were very low: MIC₉₀ and MFC₉₀ were 0.032 and 0.125 μg/ml for ketoconazole, while 0.063 and 0.25 μg/ml for itraconazole, respectively. Also, the half maximal effective concentrations (EC₅₀) of itraconazole were higher for planktonic cells and biofilms compared to ketoconazole. The EC₅₀ values of ketoconazole were 18–169 times higher and those of itraconazole 13–124 times higher for biofilms than for planktonic cells. Biofilm EC₅₀ levels exceeded MICs 103–2060 times for ketoconazole and 84–1400 times for itraconazole. No significant difference was found between these values of the two substances. In conclusion, biofilms of all examined M. pachydermatis strains were much less susceptible to ketoconazole and itraconazole than their planktonic forms.

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