Reduced virulence of melanizedCryptococcus neoformansinGalleria mellonella

Abstract

Fungal melanins are important in the virulence of many pathogenic fungi. In this study, we examined the role of melanin in the interaction between Cryptococcus neoformans and the invertebrate host, Galleria mellonella. C. neoformans was able to melanize in the presence of G. mellonella homogenate, indicating the presence of melanin substrates. Melanization was confirmed by the recovery of acid-resistant particles that were recognized by anti-melanin antibodies. In addition, we tested the effect of fungal melanization on virulence. Surprisingly, G. mellonella larvae infected with melanized fungal cells lived longer than those infected with non-melanized fungi. When the cellular immune response of G. mellonella to melanized and non-melanized cells was compared, inflammatory nodules were observed in both groups. However the response was stronger in larvae infected with melanized cells. These results suggest that fungal melanin activates the immune response of G. mellonella, thereby resulting in the decreased virulence observed with melanized cells.

Galleria mellonella: An invertebrate model to study pathogenicity in correctly defined fungal species

“…For C. neoformans, killing of larvae was shown to be more severe at 37 C, and melanization of yeast cells, morphology of the capsule and lytic activity of the haemolymph influence virulence potential and outcome. Furthermore, changes in capsule structure were observed in strains after several passages through Galleria mellonella, similar to what was shown for mammalian models (Mylonakis et al 2005;Eisenman et al 2014;Desalermos et al 2015;Trevijano-Contador et al 2015). For C. gattii it was demonstrated that major molecular types exhibit a range of virulence potential, with some strains having the potential to be more virulent than others.…”

Cryptococcus neoformansinduces antimicrobial responses and behaves as a facultative intracellular pathogen in the non mammalian modelGalleria mellonella

“…At the moment, it cannot be discarded that other factors play a role in this phenomenon. For example, C. neoformans can melanize when incubated in G. mellonella homogenates, 60 so maybe the fungus has the ability to act as a scavenger of melanin precursors from the hemolymph. When G. mellonella is infected by Beauveria bassiana, some strains also fail to induce larval melanization and in this case, this effect correlates with the production of toxins by the fungus.…”

N -Chlorotaurine Exhibits Fungicidal Activity against Therapy-Refractory Scedosporium Species and Lomentospora prolificans

“…A further challenge was to demonstrate if sublethal incubation times of NCT in vitro had an influence on the virulence of Scedosporium in an in vivo model. The virulence of Aspergillus and yeasts in the G. mellonella model was shown previously (32,(44)(45)(46), so we chose it as a practicable one. The model turned out to be suitable for S. apiospermum (IHEM 21170) and S. boydii, and a loss of virulence could be proved unambiguously after incubation in sublethal concentrations of NCT for 30 min.…”