Study on implant-associated biofilm infection established in an experimental Galleria mellonella model

The study reports in vivo biofilm infection implemented in an insect model. We mimicked implant-associated biofilm infections in Galleria mellonella larvae using toothbrush bristles and methicillin-resistant Staphylococcus aureus (MRSA). In vivo biofilm formation on bristle was achieved by sequentially injecting a bristle and MRSA into the larval hemocoel. Then, we evaluated the degree of in vivo biofilm infection by monitoring staphylococcal selective mannitol agar media cultured with bacteria harvested from bristles. As a result, it was found that biofilm formation was in progress without any external sign of infection in most of the bristle-bearing larvae for 12 h after MRSA inoculation. In addition, we investigated the antimicrobial activity of the prophenoloxidase (PPO) system in hemolymph and an antimicrobial peptide (AMP) against MRSA biofilm. The activation of the PPO system did not affect the preformed in vitro MRSA biofilms. In contrast, an AMP exerted its activity against in vitro biofilms and interfered with in vivo biofilm formation when injected into bristle-bearing larvae infected with MRSA. Finally, our confocal laser scanning microscopic analysis revealed that the biomass of the in vivo biofilm is greater compared to that of the in vitro biofilm and harbors a distribution of dead cells, which might be bacteria and/or host cells.