Abstract
Although Candida tropicalis is a frequent cause of invasive fungal diseases, its interaction with the host remains poorly studied. Galleria mellonella is a Lepidoptera model which offers a useful tool to study virulence of different microorganisms and drug efficacy. In this work we investigated the virulence of C. tropicalis in G. mellonella at different temperatures and the efficacy of antifungal drugs in this infection model. When larvae were infected with yeast inocula suspensions of different concentrations (4 × 106, 2 × 106, 106 and 5 × 105 cells/larva), we observed a dose-dependent effect on the killing of the insect (50% survival ranging from 1.4 ± 0.8 to 8.8 ± 1.2 days with the higher and lower inocula, respectively). Candida tropicalis killed G. mellonella larvae at both 30°C and 37°C, although at 37°C the virulence was more evident. Haemocytes phagocytosed C. tropicalis cells after 2 hours of infection, although the phagocytosis rate was lower when compared with other fungal pathogens, such as Cryptococcus neoformans. Moreover, the haemocyte density in the haemolymph decreased during infection and the yeast formed pseudohyphae in G. mellonella. The efficacy of amphotericin B, caspofungin, fluconazole and voriconazole was tested at different concentrations, and a protective effect was observed with all the drugs at concentrations equivalent to therapeutic dose. Fungal burden increased in infected larvae during time of infection and amphotericin B and fluconazole reduced the number of colony-forming units in the worms. Moreover, antifungal treatment was associated with the presence of cell aggregates around infected areas. We conclude that G. mellonella offers a simple and feasible model to study C. tropicalis virulence and drug efficacy.
Acknowledgements
We thank Raquel Perez Tavárez for her help in the preparation of histopathology samples and Rocío García-Rodas for her expert advice in the manipulation of G. mellonella larvae.
Declaration of interest: In the past 5 years, M. C. E. has received grant support from Astellas Pharma, bioMerieux, Gilead Sciences, Merck Sharp and Dohme, Pfizer, Schering Plough, Soria Melguizo SA, Ferrer International the European Union, the ALBAN program, the Spanish Agency for International Cooperation, the Spanish Ministry of Culture and Education, The Spanish Health Research Fund, The Instituto de Salud Carlos III, The Ramón Areces Foundation, The Mutua Madrileña Foundation. He has been an advisor/consultant to the Panamerican Health Organization, Gilead Sciences, Merck Sharp and Dohme, Pfizer, and Schering Plough. He has been paid for talks on behalf of Gilead Sciences, Merck Sharp and Dohme, Pfizer, and Schering Plough. The other authors report no conflicts of interest. The authors alone are responsible for the content and the writing of the paper. A. C. Mesa-Arango is funded by a grant from Fundación Carolina and University of Antioquia, Medellin, Colombia. A. Forastiero is funded by a fellowship from the Agencia Española de Cooperación Internacional para el Desarrollo. L. Bernal-Martínez is funded by the Spanish Network for Investigation in Infecious Pathology (REIPI). O. Z is funded by grant SAF2011-25140 from the Ministerio de Economía y Competitividad.
This paper was first published online on Early Online on 21 November 2012.