Virulence of Candida albicans mutants toward larval Galleria mellonella (Insecta, Lepidoptera, Galleridae)

Culture medium affected the virulence of a strain of Candida albicans toward Galleria mellonella larvae, but the yeast growth rates in yeast extract - peptone - dextrose broth and synthetic Galleria serum were not correlated with yeast virulence. Virulent C. albicans grew rapidly in larval serum, whereas, it limited nodulation and continued development in vivo, producing toxins that damaged the hemocytes and fat body. Nonpathogenic yeast-phase cells grew slowly in larval serum but induced extensively melanized nodules in vivo and developed no further. There was no discernible relationship in 14 exo-enzymes between the virulent and avirulent yeast strains and virulence. The avirulent myosin-I-defective yeast cells were rapidly removed from the hemolymph in vivo because of lysozyme-mediated yeast agglutination and the possible binding of the yeast cells by lysozyme and apolipophorin-III. Both lysozyme and apolipophorin-III are proteins that bind beta-1,3-glucan. Finally, insects with nonpathogenic C. albicans exhibited induced immunity and were more resistant to candidiasis from the wild-type yeast cells than were noninduced insects.