Evaluation of greater wax moth larvae, Galleria mellonella, as a novel in vivo model for non-tuberculosis Mycobacteria infections and antibiotic treatments

Purpose: To evaluate the suitability of Galleria mellonella larvae as an in vivo model and drug-screening tool for mycobacteria infections.

Methodology: Larvae were infected using a range of inoculum sizes from a variety of rapid-growing mycobacteria, including strains of M. fortuitum, M. marinum and M. aurum. Larval survival, internal bacterial burden, and the effects of amikacin, ciprofloxacin, ethambutol, isoniazid and rifampicin treatment on larval survival were measured over 144h. The effects of these anti-mycobacterial drugs on phagocytosis and circulating hemocyte numbers were also examined using microscopy.

Results: Larval survival decreased after infection with M. fortuitum and M. marinum in a dose-dependent manner, but remained unaffected by M. aurum. Heat-killed bacteria did not cause larval death. Where antibiotic monotherapy was efficacious, larval survival post-infection increased in a dose-dependent fashion. However, efficacy varied between different antibiotics and species of infecting mycobacteria and, apart from rifampicin, efficacy in vivo correlated poorly with the in vitro MICs. Combinations of antibiotics led to higher survival of infected larvae than antibiotic monotherapy. Selected antibiotic treatments that enhanced larval survival reduced the overall internal burden of infecting mycobacteria but did not eradicate the pathogens. Administration of amikacin or ethambutol to uninfected larvae induced an initial transient increase in the numbers of circulating hemocytes and reduced the phagocytic rate of hemocytes in larvae infected with M. marinum.

Conclusions: This report demonstrates the potential of employing a wax moth larvae model for studying fast-growing mycobacteria infections, and as a cheap, effective system for initial screening of novel treatments.