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JAC Advance Access originally published online on June 13, 2008
Journal of Antimicrobial Chemotherapy 2008 62(4):758-761; doi:10.1093/jac/dkn245
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

In vitro antifungal drug susceptibilities of dermatophytes microconidia and arthroconidia

Luciene M. Coelho1, Roseli Aquino-Ferreira1, Cláudia M.Leite Maffei2 and Nilce M. Martinez-Rossi1,*

1 Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil 2 Departamento de Biologia Molecular, Celular e Bioagentes Patogênicos, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil

Received 11 March 2008; returned 11 April 2008; revised 19 May 2008; accepted 27 May 2008

* Corresponding author. Tel: +55-16-3602-3078; Fax: +55-16-3633-0069; E-mail: nmmrossi{at}usp.br

Objectives: Arthroconidia have been considered as the primary cause of infection by dermatophytes. However, the in vitro antifungal testing evaluates the responses mainly of microconidia or hyphae, and dermatophytes in vivo often produce arthroconidia, a cellular structure presumably more resistant to antifungals. The aim of this study was to compare the in vitro susceptibility of microconidia and arthroconidia of Trichophyton rubrum, Trichophyton tonsurans and Trichophyton equinum to griseofulvin, itraconazole, terbinafine, fluconazole, amphotericin B and hygromycin B.

Methods: Microconidia and arthroconidia were produced in vitro, and their susceptibility to each drug was evaluated by assessing the CLSI M38-A broth microdilution method.

Results: Arthroconidia of all strains analysed appeared to be more resistant to fluconazole, griseofulvin and itraconazole than microconidia. The MIC of terbinafine was the same for microconidia and arthroconidia for all strains, and the MIC of amphotericin B for microconidia and arthroconidia was the same for isolates of T. equinum and T. tonsurans, but differed for T. rubrum. Finally, the level of resistance of microconidia for all strains towards the antibiotic hygromycin B was from 25 to 400 mg/L.

Conclusions: The difference in the susceptibility between microconidia and arthroconidia depends on the drug and on the strain, and may be one of the causes of therapeutic failure. Also, the level of resistance to the antibiotic hygromycin B presented by microconidia of these isolates will allow the use of hygromycin resistance as a dominant marker in fungal transformation procedures in future studies of gene function.

Keywords: antifungal susceptibility , dermatophytoses , MICs , Trichophyton


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