Schematic representation of Galleria mellonella insect key-immune responses to bacterial infection (A) and the proposed outcome of Brucella infection in this model (B)

Infecting bacteria are recognised by soluble pathogen recognition receptors (PRRs) that trigger granulocyte activation and secretion of a wide repertoire of antimicrobial peptides (AMPs). Phenoloxidase enzyme activates upon its release and induces the synthesis and polymerization of melanin around invading bacteria, generating cytotoxic compounds and entrapping bacteria. On top of that, plasmatocytes are attracted to the infection site and phagocytise and further decimate the bacteria. The melanised clots are finally surrounded by recruited plasmatocytes forming a nodule, further trapping bacteria and controlling the infection (Illustration created with Biorender.com).