A histological procedure to study fungal infection in the wax moth Galleria mellonella

Abstract

The invertebrate model Galleria mellonellais a widely used factitious host to study themicrobial pathogenesis in vivo. However, aspecific procedure for the recovery and the processingof the infected tissues, important for abetter understanding of the host-pathogeninteractions, has not been reported to ourknowledge. In the present study we describe anew procedure of fixation and processing oflarval tissue that allows studying the larvaltopographic anatomy and assessing the morphologicalchanges due to the fungal infection.Lepidopteran larvae were infected withCandida albicans strains displaying variousbiofilm-forming abilities. The whole larvaewere then examined for tissue changes by histologicaltechniques. We show that comparingcutting planes, serial transversal sections ofparaffin-embedded larva result in better accuracyand information recovering. Using thistechnique, it was possible to preserve theintegrity of G. mellonella internal structuresallowing the detailed analysis of morphologicaldifferences in different experimental groups(i.e., healthy vs infected larvae). We were alsoable to study strain-related differences in thepathogenesis of C. albicans by observing theimmune response elicited and the invasivenessof two isolates within the larval tissues.In general, by processing the whole larvaand optimizing routinely histochemical stainings,it is possible to visualize and analyseinfected tissues. Various degrees of pathogenicity(strain- or inoculum-related), and theinfection time course can be described indetails. Moreover, the host immune responseevents can be followed throughout the infectiousprocess leading to a comprehensive pictureof the studied phenomenon.