Observation of antibacterial effect of biodegradable polymeric nanoparticles on Staphylococcus epidermidis biofilm using FE-SEM with an ionic liquid.

We successfully visualized the antibacterial behavior of biodegradable polymeric nanoparticles (NPs) on a biofilm formed by Staphylococcus epidermidis using field emission scanning electron microscopy (FE-SEM). A hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), was applied for observation using FE-SEM. The differences in adherence and penetration behavior of three types of NPs were revealed using this method and confocal laser scanning microscopy. Biodegradable poly(dl-lactide-co-glycolide) (PLGA) NPs were prepared by the emulsion solvent diffusion method. In this study, we treated the biofilm with three PLGA NPs: unmodified PLGA, PLGA modified with chitosan (CS) and clarithromycin (CAM)-loaded + CS-modified PLGA. The viability of S. epidermidis cells treated with PLGA NPs was estimated using the LIVE/DEAD BacLight kit to understand the antibacterial ability of each NP sample in a quantitative way. The results confirmed that CAM-loaded + CS-modified PLGA had high antibacterial ability on the biofilm. This novel observation technique would be useful in the development of drug formations and medical agents.