The non-mammalian hostGalleria mellonellacan be used to study the virulence of the fungal pathogenCandida tropicalisand the efficacy of antifungal drugs during infection by this pathogenic yeast

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 × 10(6), 2 × 10(6), 10(6) and 5 × 10(5) 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.

Histological Observation and Expression Patterns of antimicrobial peptides during Fungal Infection in Musca domestica (Diptera: Muscidae) Larvae

“…In these environments, C. albicans was able to develop from the yeast to hyphal form (Huang 2012;Mayer et al 2013). Our data are consistent with previous research reporting the formation of pseudomycelium by Candida tropicalis mycothallus when hemocyte numbers were reduced in G. mellonella (Mesa-Arango et al 2013). Some reports suggested that insect blood cells were constantly regenerated and kept dynamically changing.…”

Candida tropicalis Antifungal Cross-Resistance Is Related to Different Azole Target (Erg11p) Modifications

“…Galleria mellonella larvae were infected with an inoculum of 2 ϫ 10 6 CFU/larva when strain ATCC 750, CL-6835, or TP-13650 was used. An inoculum of 4 ϫ 10 6 CFU/larva was used for ATCC 200956, since this strain shows reduced virulence in this model (37). In all cases, 80% of infected and untreated larvae died between the 3rd and 4th day postinfection.…”

“…Among these, Galleria mellonella presents certain benefits in comparison with other nonmammalian models of infection (31). Previous studies have documented that G. mellonella is a valid model for the evaluation of microbial virulence and/or the efficacies of different antimicrobial agents against infections caused by different bacteria and fungi (32)(33)(34)(35)(36)(37)(38).…”

An alternative host model of a mixed fungal infection by azole susceptible and resistantAspergillusspp strains

“…Wax moth larvae killing assays were carried out as described previously. 24,25 Briefly, groups of 10 larvae (0.3-0.5 g, Alcotan S.L., Valencia, Spain) were inoculated with 10 mL of a 10 7 conidia/ml suspension in PBS into the haemocoel, so the final inoculum in each group was 10 5 conidia per larva. Mixed infected larvae were inoculated with A. fumigatus and A. lentulus (ratio 1:1) to a final concentration of 10 5 conidia per larvae.…”