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Biofilms have caused many problems, not only in the industrial fields, but also in our daily lives. Therefore, it is important for us to control them by evaluating them properly. There are many instrumental analytical methods available for evaluating formed biofilm qualitatively. These methods include the use of Raman spectroscopy and various microscopes (optical microscopes, confocal laser microscopes, scanning electron microscopes, transmission electron microscopes, atomic force microscopes, etc.). On the other hand, there are some biological methods, such as staining, gene analyses, etc. From the practical viewpoint, staining methods seem to be the best due to various reasons. Therefore, we focused on the staining method that used a crystal violet solution. In the previous study, we devised an evaluation process for biofilms using a color meter to analyze the various staining situations. However, this method was complicated and expensive for practical engineers. For this experiment, we investigated the process of using regular photos that were quantified without any instruments except for digitized cameras. Digitized cameras were used to compare the results. As a result, we confirmed that the absolute values were different for both cases, respectively. However, the tendency of changes was the same. Therefore, we plan to utilize the changes before and after biofilm formation as indicators for the future. [ABSTRACT FROM AUTHOR]

Biofilms are a result of bacterial activities and are found everywhere. They often form on metal surfaces and on the surfaces of polymeric compounds. Biofilms are sticky and mostly consist of water. They have a strong resistance to antimicrobial agents and can cause serious problems for modern medicine and industry. Biofilms are composed of extracellular polymeric substances (EPS) such as polysaccharides produced from bacterial cells and are dominated by water at the initial stage. In a series of experiments, using Escherichia coli, we developed three types of laboratory biofilm reactors (LBR) to simulate biofilm formation. For the first trial, we used a rotary type of biofilm reactor for stirring. For the next trial, we tried another rotary type of reactor where the circular plate holding specimens was rotated. Finally, a circular laboratory biofilm reactor was used. Biofilms were evaluated by using a crystal violet staining method and by using Raman spectroscopy. Additionally, they were compared to each other from the practical (industrial) viewpoints. The third type was the best to form biofilms in a short period. However, the first and second were better from the viewpoint of "ease of use". All of these have their own advantages and disadvantages, respectively. Therefore, they should be properly selected and used for specific and appropriate purposes in the future. [ABSTRACT FROM AUTHOR]

The evaluation of biofilm formation is important, given the ubiquity and problematic nature of biofilms in industrial and medical settings, as well as in everyday life. Basically, biofilms are formed on substrates. Therefore, it is essential to consider the properties of the substrates during biofilm evaluation. The common dye staining method to evaluate biofilm formation requires a short evaluation time and enables the evaluation of a large area of the sample. Furthermore, it can be easily determined visually, and quantitative evaluation is possible by quantifying color adsorption. Meanwhile, the dye staining method has the problem of adsorption even on substrate surfaces where no biofilm has formed. Therefore, in this study, we focused on Ag+ reduction reaction to devise a novel biofilm evaluation method. Ag+ is highly reductive and selectively reacts with organic substances, such as saccharides, aldehydes, and proteins contained in biofilms, depositing as metallic Ag. First, to simply evaluate biofilm formation, we used a glass substrate as a smooth, transparent, and versatile oxide material. We observed that the amount of Ag deposited on the substrate was increased proportionally to the amount of biofilm formed under light irradiation. Upon comparing the Ag deposition behavior and adsorption behavior of crystal violet, we discovered that for short immersion times in AgNO3 solution, Ag deposition was insufficient to evaluate the amount of biofilm formation. This result suggests that the Ag reduction reaction is more insensitive than the crystal violet adsorption behavior. The results of the Ag deposition reaction for 24 h showed a similar trend to the crystal violet dye adsorption behavior. However, quantitative biofilm evaluation using the proposed method was difficult because of the Ag+ exchange with the alkali metal ions contained in the glass substrate. We addressed this issue by using the basic solution obtained by adding an ammonia solution to aqueous AgNO3. This can cause Ag+ to selectively react with the biofilm, thus enabling a more accurate quantitative evaluation. The optimum was determined at a ratio of distilled water to aqueous ammonia solution of 97:3 by weight. This biofilm was also evaluated for materials other than ceramics (glass substrate): organic material (polyethylene) and metal material (pure iron). In the case of polyethylene, a suitable response and evaluation of biofilm formation was successfully achieved using this method. Meanwhile, in the case of pure iron, a significantly large lumpy deposit of Ag was observed. The likely reason is that Ag precipitation occurred along with the elution of iron ions because of the difference in ionization tendency. It could be concluded that the detection of biofilm formation using this method was effective to evaluate biofilm formation on materials, in which the reduction reaction of [Ag(NH3)2]+ does not occur. Thus, a simple and relatively quantitative evaluation of biofilms formed on substrates is possible using this method. [ABSTRACT FROM AUTHOR]