In vitro inactivation effect of blue light emitting diode (LED) on Shiga-toxin-producing Escherichia coli (STEC)

The antimicrobial effects of blue LED were investigated on seven Shiga-toxin-producing Escherichia coli strains (STEC 7 serotypes) using two LED formats at 405 nm (Prototype A, bulb array emitting 22.77 ± 1.054 mW/cm2; Prototype B, strip array emitting 4.25 ± 0.25 mW/cm2). For both prototypes, cytotoxic effects were detected with time-dependent light dosages and antimicrobial activity of 405 nm blue LED was most effective on minimal medium agar and Luria-Bertani (LB) agar, less effective on cooked meat agar, and least effective on sheep blood agar. Inactivation kinetics of individual STEC strains were determined within a dosage of 163.96 ± 7.55 J/cm2, 5–7 log10 cfu reduction was observed in 7 log10 cfu/ml LB suspension test among seven strains and no viable cells were detected in 3 log10 cfu/ml LB suspension test for all seven tested strains. Difference in light susceptibility among the tested strains was observed between the two prototypes with O111 strain being the most sensitive strain. Multiple factors (e.g. nutrient availability, treatment time, distance, and temperature) could be associated with the antimicrobial effect of 405 nm blue light and need to be well considered when using the technology under different food processing scenarios.