Abstract
Malassezia furfur and Malassezia pachydermatis are lipophilic and lipid dependent yeasts, associated with the skin microbiota in humans and domestic animals, respectively. Although they are commensals, under specific conditions they become pathogens, causing skin conditions, such as pityriasis versicolor, dandruff/seborrheic dermatitis, folliculitis in humans, and dermatitis and otitis in dogs. Additionally, these species are associated with fungemia in immunocompromised patients and low-weight neonates in intensive care units with intravenous catheters or with parenteral nutrition and that are under-treatment of broad-spectrum antibiotics. The host-pathogen interaction mechanism in these yeasts is still unclear; for this reason, it is necessary to implement suitable new host systems, such as Galleria mellonella. This infection model has been widely used to assess virulence, host-pathogen interaction, and antimicrobial activity in bacteria and fungi. Some advantages of the G. mellonella model are: (1) the immune response has phagocytic cells and antimicrobial peptides that are similar to those in the innate immune response of human beings; (2) no ethical implications; (3) low cost; and (4) easy to handle and inoculate. This study aims to establish G. mellonella as an in vivo infection model for M. furfur and M. pachydermatis. To achieve this objective, first, G. mellonella larvae were first inoculated with different inoculum concentrations of these two Malassezia species, 1.5 × 106 CFU/mL, 1.5 × 107 CFU/mL, 1.5 × 108 CFU/mL, and 11.5 × 109 CFU/mL, and incubated at 33 and 37°C. Then, for 15 days, the mortality and melanization were evaluated daily. Finally, the characterization of hemocytes and fungal burden assessment were as carried out. It was found that at 33 and 37°C both M. furfur and M. pachydermatis successfully established a systemic infection in G. mellonella. M. pachydermatis proved to be slightly more virulent than M. furfur at a temperature of 37°C. The results suggest that larvae mortality and melanization is dependent on the specie of Malassezia, the inoculum concentration and the temperature. According to the findings, G. mellonella can be used as an in vivo model of infection to conduct easy and reliable approaches to boost our knowledge of the Malassezia genus.
Highlights
In the case of larvae infected with M. pachydermatis, no significant difference in larval survival was found between control larvae and inoculum concentration of 1.5 × colony-forming units (CFU)/mL, and for the two remaining inoculum concentrations (1.5 × and 1.5 × CFU/mL), it was observed that larval survival decreased (p < 0.0001, log-rank [(Mantel-Cox]) test)
It was demonstrated that M. furfur and M. pachydermatis were able to establish a systemic infection in G. mellonella larvae at 33◦C, experiments were conducted at 37◦C to evaluate the systemic infection at the human corporal temperature
G. mellonella has been successfully implemented as an infection model of fungal pathogens, like Madurella mycetomatis (Kloezen et al, 2015), Cryptococcus neoformans (Eisenman et al, 2014), Aspergillus flavus (Scully and Bidochka, 2005), Candida albicans (Amorim-Vaz et al, 2015), Candida tropicalis (Mesa-Arango et al, 2013), and dermatophytes (Achterman et al, 2011; Ishii et al, 2017)
Summary
The genus Malassezia is comprised of 18 lipophilic species characterized as commensal yeasts, which are part of the skin mycobiota of both humans and animals (Nagata et al, 2012; Cabañes, 2014; Cabañes et al, 2016; Honnavar et al, 2016; Prohic et al, 2016), and are commonly located in lipid-rich body areas, such as the scalp, face, and trunk (Gupta et al, 2004; DeAngelis et al, 2005) Some species of this genus have been associated with skin diseases (Gupta et al, 2004; Prohic et al, 2016) and systemic infections (Gaitanis et al, 2012; Kaneko et al, 2012; Nagata et al, 2012; Iatta et al, 2014, 2018; Roman et al, 2016; Lee et al, 2018; Theelen et al, 2018; Chen et al, 2020). Using fluconazole to prevent Candida spp. infections promotes colonization of resistant M. furfur (Chen et al, 2020)
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