Malassezia furfur and Malassezia pachydermatis as 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 and folliculitis in humans. In addition, these species are associated with fungemia in immunocompromised patients and low-weight neonates in intensive care units (ICUs) with intravenous catheters or with parenteral nutrition and that are under-treatment of broad-spectrum antibiotics.

However, the host-pathogen interaction mechanism in these yeasts remains unclear. Hence, it is necessary to implement suitable new host systems, such as Galleria mellonella – used to assess virulence, host-pathogen interaction and antimicrobial activity in bacteria and fungi.

The objective of a new study published in Frontiers in Cellular and Infection Microbiology was to establish G. mellonella as an in vivo infection model for M. furfur and M. pachydermatis.

In this experiment, G. mellonella larvae were 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. Thereafter, the mortality and melanization were evaluated daily, for 15 days. Then, the characterization of hemocytes and fungal burden assessment were as carried out.

The findings revealed that at 33 and 37°C both M. furfur and M. pachydermatis successfully established a systemic infection in G. mellonella. While M. pachydermatis proved to be slightly more virulent than M. furfur at a temperature of 37°C.

From the results, it was concluded that larvae mortality and melanization is dependent on the specie of Malassezia, the inoculum concentration and the temperature.

Source: Frontiers in Cellular and Infection Microbiology. 2020 May 5;10:199. doi: 10.3389/fcimb.2020.00199. eCollection 2020.