Establishing an invertebrate <i>Galleria mellonella</i> greater wax moth larval model of <i>Neisseria gonorrhoeae</i> infection

<i>Neisseria gonorrhoeae</i> (gonococcus) causes the human sexually transmitted disease gonorrhea. Studying gonococcal pathogenesis and developing new vaccines and therapies to combat the increasing prevalence of multi-antibiotic resistant bacteria has made use of many <i>ex vivo</i> models based on human cells and tissues, and <i>in vivo</i> vertebrate models, for example, rodent, pig and human. The focus of the current study was to examine the utility of the invertebrate greater wax moth <i>Galleria mellonella</i> as an <i>in vivo</i> model of gonococcal infection. We observed that a threshold of ~10⁶ – 10⁷ gonococci/larva was required to kill &gt;50% of larvae (P &lt; 0.05), and increased toxicity correlated with reduced health index scores and pronounced histopathological changes such as increases in the total lesion grade, melanized nodules, hemocyte reaction, and multifocal adipose body degeneration. Larval death was independent of the expression of pilus or Opa protein or LOS sialylation within a single gonococcal species studied, but the model could demonstrate relative toxicity of different isolates. <i>N. meningitidis, N. lacatamica</i> and gonococci all killed larvae equally, but were significantly less toxic (P &gt; 0.05) than <i>Pseudomonas aeruginosa</i>. Larvae primed with nontoxic doses of gonococci were more susceptible to subsequent challenge with homologous and heterologous bacteria, and larval survival was significantly reduced (P &lt; 0.05) in infected larvae after depletion of their hemocytes with clodronate-liposomes. The model was used to test the anti-gonococcal properties of antibiotics and novel antimicrobials. Ceftriaxone (P &lt; 0.05) protected larvae from infection with different gonococcal isolates, but not azithromycin or monocaprin or ligand-coated silver nanoclusters (P &gt; 0.05).