Biofilms formed on metallic materials by E. coli and S. epidermidis and their evaluation by crystal violet staining and its reflection

Bacteria form biofilms by attaching to materials. The formed biofilm has various influences on daily life and industry, positively or negatively. Therefore, the biofilm should be observed and controlled in an appropriate manner. There are numerous developed methods to evaluate biofilms. However, many of them have been not appropriate from the viewpoint of industrial application since they are difficult to be handled and the associated pieces of equipment are very expensive. Therefore, in this study, the authors focused on staining methods to evaluate biofilms. Crystal violet is well known to stain negatively charged parts of polymeric substances, such as polysaccharides and other polar polymers. Thus, the amount and contents were expected to evaluate reliably. In this study, the authors compared Raman shifts and colour measurements for biofilms formed on four metallic materials by Escherichia coli and Staphylococcus epidermidis. It could be confirmed that staining by crystal violet could predict the amounts of biofilms, and the contents ratio (particularly the contents of polysaccharides) to some extent.