Cryptococcus neoformans Capsular Enlargement and Cellular Gigantism during Galleria mellonella Infection

Abstract

We have studied infection of Cryptococcus neoformans in the non-vertebrate host Galleria mellonella with particular interest in the morphological response of the yeast. Inoculation of C. neoformans in caterpillars induced a capsule-independent increase in haemocyte density 2 h after infection. C. neoformans manifested a significant increase in capsule size after inoculation into the caterpillar. The magnitude of capsule increase depended on the temperature, being more pronounced at 37°C than at 30°C, which correlated with an increased virulence of the fungus and reduced phagocytosis at 37°C. Capsule enlargement impaired phagocytosis by haemocytes. Incubation of the yeast in G. mellonella extracts also resulted in capsule enlargement, with the polar lipidic fraction having a prominent role in this effect. During infection, the capsule decreased in permeability. A low proportion of the cells (<5%) recovered from caterpillars measured more than 30 µm and were considered giant cells. Giant cells recovered from mice were able to kill the caterpillars in a manner similar to regular cells obtained from in vivo or grown in vitro, establishing their capacity to cause disease. Our results indicate that the morphological transitions exhibited by C. neoformans in mammals also occur in a non-vertebrate host system. The similarities in morphological transitions observed in different animal hosts and in their triggers are consistent with the hypothesis that the cell body and capsular responses represent an adaptation of environmental survival strategies to pathogenesis.

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

“…14 Previous studies have documented that G. mellonella is a valid model to evaluate the microbial virulence and/or the efficacy of different antimicrobial agents in infections caused by different bacteria 37 and fungi, such as C. neoformans, 38,39 Candida spp, 40,41 Histoplasma spp. 42 and A. fumigatus.…”

The Cryptococcus neoformans Capsule: a Sword and a Shield

“…For example, C. neoformans recovered from different organs during murine infections demonstrates variable binding to anticapsule antibodies (64). Additionally, experimental infection of Galleria mellonella wax moth larvae results in capsules with increased density compared to those of identical strains grown in vitro, as measured by the penetrance of antibody binding (70). The changes in capsule structure, size, and density are potentially a mechanism for escape or evasion from the immune system, demonstrating that capsule is a dynamic structure that is highly regulated by the cell in response to specific environmental cues.…”

“…One of the differences in titan cell capsule is the increased size and number of chitin-like structures in the capsule (70). These structures may be related to the increased resistance of titan cell capsule to radiation, organic solvents, and dimethyl sulfoxide (DMSO) (226).…”

“…Investigators have speculated that this capsule may protect the fungus from environmental desiccation and/or natural predators, such as nematodes or amoebae (39,70,150,191,192,226). In the host, the capsule serves many protective functions, including reducing host immune responses by downregulating inflammatory cytokines, depleting complement components, and inhibiting the antigenpresenting capacity of monocytes (174,200,201).…”

Modeling Klebsiella pneumoniae Pathogenesis by Infection of the Wax Moth Galleria mellonella

“…Since virulence gene expression is frequently regulated by temperature, it is likely that temperature requirements bias gene expression and affect the pathogen response to these hosts. The larva of the wax moth Galleria mellonella is emerging as a reliable model host for studying the pathogenesis of many human pathogens because, among other advantages, G. mellonella can grow at 37°C (11)(12)(13)(14)(15)(16)(17)(18). However, there is a paucity of information on the extent to which the infection of G. mellonella can mimic the interplay between the innate immune system and human pathogens.…”