Development of teaching materials to visualize the bactericidal effect of ultraviolet rays using Escherichia coli as a bioassay

Abstract

In this study, we examined the development of teaching materials that can visualize the bactericidal effect of ultraviolet rays by using Escherichia coli as a bioassay. The uniqueness of this study is that a dilution of a non-pathogenic Escherichia coli strain (Escherichia coli DH5α strain) was sprayed from a spray bottle onto agar medium, half of which was covered with aluminum foil, irradiated with ultraviolet rays or sunlight, and cultured at 37°C for 24 hours. In the method of planting Escherichia coli in a medium, the spraying method from a spray bottle had not been used in previous studies. This spraying method was able to achieve an even diffusion of colonies. In addition, by using the area covered with aluminum foil or ultraviolet blocking film as a control, the comparison of the number of colonies with or without ultraviolet rays and sunlight was clarified, and the bactericidal action was visualized and quantified. Moreover, the difference in the amount of ultraviolet rays between sunny and cloudy weather was clearly visualized. The results of practicing the teaching materials developed in this study in a workshop for high school students confirmed that they improved their awareness and understanding the bactericidal action of ultraviolet rays. Furthermore, the results for teachers suggested that the use of his teaching material would be useful in inquiry activities.