Galleria mellonella experimental model: advances and future directions.

For the last 20 years, the greater wax moth Galleria mellonella has gathered widespread interest in the scientific community as a model host. During this time, there has been an increase in the number of studies utilizing G. mellonella as an alternative model host. These studies have provided important ‘proof of concept’ findings, leading to important advances on health sciences. Recently, the entire genome of G. mellonella was sequenced (Lange et al. 2018) raising further insights and perspectives for future investigations. Aimed at giving an updated overview, the thematic issue on the G. mellonella as experimental model gathers a collection of research articles and reviews by renowned research groups from Australia, Brazil, India, Ireland, Poland, Spanish, United Kingdom and USA. Among the research articles, original studies focusing on the pathogenetic mechanisms of different human pathogens (Romera et al. 2020; Bruchmann et al. 2021), as well as their interaction with the immune system (Staczek et al. 2020), are presented. Bruchmann et al. (2021) performed the first genomescale analysis for identifying virulence determinants of Klebsiella pneumoniae associated with infection outcome in G. mellonella. Using Transposon Directed Insertion Site (Tra-DIS) sequencing, the authors demonstrated a dominant function of surface polysaccharides, with additional contributions of siderophores, surface proteins and purine biosynthesis genes. In addition to specific findings, the study proves the capacity of G. mellonella in dissecting the bacterial virulence mechanisms in molecular levels (Bruchmann et al. 2021). Staczek et al. (2020) thoroughly investigated the role of Aspergillus niger α-1,3-glucan in activating the immune system of G. mellonella. Their results suggest that the fungal α-1,3-glucan has a dual role and not only stimulates the insect cellular immune response, but also decreases the apolipophorin-III level in the hemocytes, making the fungal infection a result from the imbalance between both effects. This thematic issue also brings novel therapeutic perspectives for infectious diseases, including the repurposing of antiviral drug zidovudine (AZT) combined with meropenem as a potential treatment for K. pneumonia infection (DeSarno, Parcell and Coote 2020) and the identification of a short-chain antimicrobial hybrid peptide, Cecropin A (1–7)Melittin (CAMA), with efficacy on multi-drug resistant Eschericha coli strains (Vergis et al. 2021). To standardize and improve the reliability of G. mellonella as a model for antimicrobial tests, Hesketh-Best et al. (2021) investigated the effects of weight on mortality of G. mellonella infected by Methicilin-Resistant Staphylococcus aureus (MRSA). Several linear regression models were implemented as a tool to guide the experimental design in future studies, including the linear model for 50% lethal dose (LD50) based on the weight, lipid content and length of G. mellonella larvae. In addition, the thematic issue includes research articles related to oral bacteria and animal pathogens of particular importance in the dental and veterinary fields, respectively. Santos et al. (2020) reported that a probiotic strain of Lactobacillus reuteri was able to protect G. mellonella from Fusobacterium nucleatum infection, an important periodontopathogenic bacteria. Therefore, this study raises the possibility of controlling periodontal diseases with a natural and noninvasive method. In relation to veterinary pathogens, Crispim et al. (2020) unveiled the role of hfq gene in the porcine bacteria Actinobacillus pleuropneumoniae. Interestingly, their findings indicate that hfq gene is a pleiotropic global regulator with role in the adhesion to biotic and abiotic surfaces, resistance to various stress conditions and virulence in G. mellonella. Besides these original articles, the thematic issue includes several comprehensive reviews that outline state-of-the-art discussions and reflections on the use of G. mellonella as an infection model. In these reviews, experts in the field share their experiences through a direct and didactic way. Wojda et al. (2020) presents a detailed overview on the biology and behavior of G. mellonella, providing knowledge for both beginner and advanced scientists. In another review, Pereira et al. (2020) trace a global outline of the successful applications of G. mellonella model and give practical recommendations for larval rearing and experimental assays. Indeed, although G. mellonella is a well-established model, some aspects still need to be standardized. For example, Piatek, Sheehan and Kavanagh (2020) discuss the specificity of inoculation methods for each microorganism, highlighting the importance of force-feeding or gavage for the study of enteropathogens. Seeking to close knowledge gaps on G. mellonella immune mechanisms, Smith and Casadevall (2021) provide a detailed comparison between mammals and G. mellonella in relation to pattern recognition receptors, extracellular immune response, complement and complement-like system, immune cell responses, antioxidant defenses and persistence within phagolysosome. Finally, an exciting review by Dinh et al. (2021) discusses the future of the G. mellonella experimental model in the molecular age. A multitude of new applications for G. mellonella are addressed based on genomic, transcriptomic, proteomic and genetic manipulation approaches, contributing to make G. mellonella a sophisticated model for in vivo studies. Based on its current and future relevance, this thematic issue will culminate in the upcoming ‘Galleria mellonella workshop (GmW)’ that will be