Biofilm formation of Staphylococcus epidermidis imaged using atmospheric scanning electron microscopy.

Staphylococcus epidermidis are gram-positive bacteria that form a biofilm around implanted devices and develop an infection into a chronic state. Recently, it has been revealed that microvesicles have important roles in biofilm formation and intercellular communication among bacteria. However, biofilm formation of Staphylococcus epidermidis, and its relation to microvesicle secretion, is poorly understood because of the difficulty required to preserve the delicate water-rich morphology of biofilm for high-resolution observations. Here, we successfully imaged the microvesicles secreted from Staphylococcus epidermidis and the subsequent process of their integration into biofilm using liquid-phase imaging using atmospheric scanning electron microscopy (ASEM). In the biofilm, cells were connected by nanotube-like structures attached by microvesicles, and surrounded by extracellular polymeric substances. Cells cultured in the ASEM specimen holder were aldehyde-fixed and stained using positively charged nanogold labelling and/or using National Center for Microscopy and Imaging Research method. The samples immersed in aqueous radical scavenger glucose buffer were imaged by the inverted SEM of ASEM. Information regarding the morphologies of microvesicles, nanotube-like fibrils, and biofilm formed by Staphylococcus epidermidis is expected to be useful to elucidate the biological mechanism of biofilm formation and to develop a medicine against biofilms and their associated infections.