Electron microscopy of Staphylococcus epidermidis fibril and biofilm formation using image-enhancing ionic liquid.

We established an optimized biofilm observation method using a hydrophilic ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). In the present study, a biofilm was formed by Staphylococcus epidermidis. Using field emission (FE) scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the colonization of assemblages formed by microbial cells was observed as a function of the cultivation time. FE-TEM analysis revealed that the fibril comprises three types of protein. In addition, the ultrastructure of each protein monomer was visualized. It was expected that the curly-structured protein plays an important role in extension during fibril formation. Compared to the conventional sample preparation method for electron microscopy, a fine structure was easily obtained by the present method using IL. This observation technique can provide valuable information to characterize the ultrastructure of the fibril and biofilm that has not been revealed till date. Furthermore, these findings of the molecular architecture of the fibril and the colonization behavior of microbial cells during biofilm formation are useful for the development of antibacterial drugs and microbial utilization.