Objective

Background: Galleria mellonella can be used as an in vivo model system for a range of fungi, Gram-negative and Gram-positive bacterial pathogens. Use of Galleria mellonella, wax moth larvae, as an infection model is becoming increasingly popular due to its proven ability to determine bacterial virulence and lethal dose, and assess the toxicity and efficacy of novel compounds. Biosystems Technology have developed research grade G. mellonella (TruLarv^TM), free of hormones and antibiotics, to provide a low cost, robust, high throughput, ethical model system.

 

Materials/methods: Our model system uses TruLarv and bioluminescent bacterium, such as Pseudomonas aeruginosa strain Xen41 (a derivative of PA01) that has been genetically engineered to express the Photorhabdus luminescens lux operon, to assess the efficacy of antimicrobial compounds. TruLarv were infected with a lethal dose of bioluminescent bacterium and treated 2 hours post infection with a range of antimicrobial doses. Survival was monitored, and luminescence measured using GloMAX and/or IVIS technology.

 

Results: We have shown that the bioluminescence measured within infected G. mellonella can be linked to survival (and CFU burden) of individual larvae. The levels of luminescence exhibited by the Xen41 infected Galleria (between 10⁵ - 10⁶ RLU) showed a significant difference in luminescence signal when compared to treated or vehicle control groups which display a luminescence signal between 10² - 10³ RLU. Our Galleria time-kill curve analysis have shown comparable luminescence and CFU/mL results, both showing a dose response with increasing antibiotic concentrations, with the decline in luminescence seen being directly comparable with the drop in bacterial burden within individual larvae. We have shown that luminescence signal correlates directly with survival rate of individual infected larvae, allowing us to gain a better understanding of the efficacy of antimicrobial compounds over time and thus help determine suitable dosing regimens for use in future in vivo studies.

 

Conclusions: Our system can be applied to other bacterial pathogens and bacterial luminescent strains to assess the efficacy of novel antimicrobial compounds, prior to their use mammalian in vivo model systems. We envisage the use of G. mellonella TruLarvand luminescent bacterium will provide a cost effective pre-in vivo model system for toxicity and efficacy testing of novel compounds, and will subsequently reduce the number of animals used in subsequent studies and time taken for initial in vitro screening.