Wax moth larva (Galleria mellonella): an in vivo model for assessing the efficacy of antistaphylococcal agents

Objectives: The aim of this study was to investigate whether the wax moth larva, Galleria mellonella, is a suitable host for assessing the in vivo efficacy of anti-staphylococcal agents against S. aureus and MRSA infections.
Methods: Wax moth larvae were infected with increasing doses of S. aureus to investigate the effect of inoculum size on larval survival. In addition, infected wax moth larvae were treated with daptomycin, penicillin and vancomycin to examine whether these agents were effective against S. aureus and MRSA infections in vivo.
Results: Increasing inoculum doses of live S. aureus cells resulted in greater larval mortality but heat-killed bacteria and cell-free culture filtrates had no detrimental effects on survival. Larval mortality rate also depended on the post-inoculation incubation temperature. After larvae were infected with S. aureus, larval survival was enhanced by administering the anti-staphylococcal antibiotics, daptomycin and vancomycin. Larval survival increased with increasing doses of the antibiotics. Moreover, penicillin improved survival of larvae infected with a penicillin-susceptible methicillin-susceptible S. aureus (MSSA) strain but it was ineffective at similar doses in larvae infected with MRSA (penicillin-resistant). Daptomycin and vancomycin were also effective when administered to the larvae prior to infection with bacteria.
Conclusions: This is the first report to demonstrate that antibiotics are effective in the wax moth larva model for the treatment of infections caused by Gram-positive bacteria. The new wax moth larva model is a useful preliminary model for assessing the in vivo efficacy of candidate anti-staphylococcal agents before proceeding to mammalian studies, which may reduce animal experimentation and expense.