Identification and characterisation of human pathogenic filamentous fungi and susceptibility to Thymus schimperi essential oil

Abstract

Twenty-eight clinical fungal isolates were characterised by morphological (macro- and micro-features and growth response at 25, 30 and 37°C) and molecular (nuclear rDNA-internal transcriber spacer, calmodulin, cytochrome c oxidase 1 and the largest subunit of RNA polymerase II) analyses. The clinical fungal isolates were ascribed to the following taxa: Penicillium chrysogenum, Verticillium sp., Aspergillus tubingensis, Aspergillus minutus, Beauveria bassiana and Microsporum gypseum. In addition, in vitro susceptibility testing of the isolates to conventional antifungal agents and to two chemically well-defined chemotypes of Thymus schimperi essential oil was performed. Most of the isolates were resistant to amphotericin B (except A. minutus), and itraconazole, while terbinafine was quite active on these fungi. T. schimperi essential oil showed antifungal activity against all of the tested fungal isolates with minimal inhibitory concentration values similar or lower than those of terbinafine. Transmission electron microscopy analyses revealed that fungal growth inhibition by essential oil was accompanied by marked morphological and cytological changes.