Candida parapsilosis, Candida orthopsilosis, and Candida metapsilosisvirulence in the non-conventional host Galleria mellonella

The incidence of fungal infections due to C. parapsilosisand closely related cryptic species (-psilosiscomplex) has increased in the last few years, but differences in virulence among these species have not been widely studied. Fifteen clinical isolates of C. parapsilosis, C. orthopsilosis, and C. metapsilosis, including the type strains, were used to evaluate their virulence in Galleria mellonellalarvae. Fluctuations in the hemocyte density and in the phagocytic activity were also tested. Differences in the median survival for these species were demonstrated at 37 °C (2.6 ± 1.02, 2.3 ± 0.92, and 4.53 ± 1.65 d for C. parapsilosis, C. orthopsilosis, and C. metapsilosis, respectively). Galleria mellonellahemocytes phagocytosed C. metapsilosisstrains more effectively than did for C. orthopsilosisand C. parapsilosis(P< 0.05). The phagocytosis rate was lower for C. parapsilosisthan for C. orthopsilosis(P< 0.05). The hemocyte density was increased in larvae infected with C. metapsilosiscompared with those infected with C. parapsilosisor C. orthopsilosis(P< 0.05). Moreover, in vitro studies of virulence factors such as pseudohyphae production and hydrolytic enzyme secretion showed that the capability of C. metapsilosisstrains to produce those virulence factors was reduced. Infections due to -psilosiscomplex species produced tissue damage in G. mellonellaand pseudohyphae could be also observed during infection with C. parapsilosis.