Epsilon Archive for Student Projects

Abstract

Recent research in the field of microbiology has shown a potential for certain wavelengths of light
within the visible spectrum to directly influence behavior of Escherichia coli (E. coli). These
established pattern changes (such as motility, flagella effectiveness, and the formation of biofilms)
highlight the role of a photoreceptor in the bacteria that alters regular behavior. At established
wavelengths and doses of visible light, Reactive Oxygen Species can accumulate within cells causing significant damage—potentially even mortality. This has also been shown to be affective with different wavelengths in the ultraviolet (UV) spectrum which has far reaching applications (sterilization of surgical equipment, etc.), but cannot be used with living cells prone to damage from UV radiation. This project attempted to determine the wavelength and fluence within the blue region of the visible spectrum to generate the greatest photodynamic inhibition of E. coli. 400 nm had the
greatest inhibition effect with a 2.21 log CFU/ml decrease after a dose of 150,844 mJ/cm2. 420 nm (1.19 log CFU/ml decrease) and 450 nm (0.11 log CFU/ml decrease) showed significantly less inhibition after the same dose. In order to ensure that the media (Luria-Bertani with ampicillin and arabinose) did not accelerate the exposure effect of blue light, arabinose was removed from the growth media and the experiment was repeated with 400 nm radiation. This sample started with higher levels of growth after minimal exposure, but after full fluence (150,844 mJ/cm2), the sample had a similar level of CFU/ml as the samples grown with arabinose in the media (p = 0.12). After exposure, samples were placed in cold storage at 4 C for up to 16 days in the growth media. This was to recreate the longest storage conditions of fresh produce in order to evaluate the regrowth potential of the pathogen. The sample exposed to the highest blue light radiation (150,844 mJ/cm2) had the lowest regrowth compared to the control, ending 3 log units below in CFU/ml. Given the results of this project, blue light could become a powerful tool in sterilization of items such as fresh produce. The surface of leafy greens, such as baby leaf spinach, is a known pathway for Shiga toxin�producing E. coli (STEC), such as E. coli O157:H7, to enter the food chain causing a potentially deadly pathogenic outbreak, so any added safety hurdles must be thoroughly considered.