Inactivating Escherichia coli using hexagonal array of narrow bandwidth of violet-blue light emitting diode

Abstract

Antibiotic resistance, in general, and multi-drug resistant Escherichia coli, in particular, have caused a significant burden on modern therapeutics. In order to find alternatives besides researching new antibiotics, numerous antimicrobial methods have been used, and light-emitting diode (LED) emitting light in blue regions is increasing attention. This work utilized a LED array of six hexagonal III-Nitride based-LEDs with a wavelength of 404.2 nm (bandwidth ± 7.2 nm) to demonstrate the antimicrobial photodynamic effect on E. coli. Bacterial cultures were inactivated under blue light LED array at 2 cm, 5 cm, 7 cm, and 10 cm. In addition, the correlation between dose energy, exposure distance, and irradiation time was also evaluated. A complete inactivation was achieved at 2 cm, 5 cm, and 7 cm with an irradiation time of 16 min, 35 min, and 35 min, respectively. When exposed at 10 cm and irradiated for up to 90 min, the inactivation was only 90% (equivalent to 106 CFU/mL) and showed fluctuation. Regardless of the energy dosage, less energy was released at a greater distance, in which at 7 cm, the LED emitted 160 J/cm2 compared to over 850 J/cm2 of 2 cm distance. However, the irradiation time was increased from 16 min to 35 min. Thus, the results showed that the antibacterial effect of the LEDs was dependent on the distance, the irradiation time, and the energy dose. This study suggests the potential of 405 nm LEDs as antimicrobial methods for preventing antibiotic resistance. Noteworthy that a low energy dose, at an exposure distance of 10 cm, prevents the complete inactivation due to hormesis.

Keywords

• Escherichia coli
• LED array
• Photodynamic
• Irradiation time
• Exposure distance
• Hormesis