Antimicrobial effect of blue light on antibiotic-sensitive and drug-resistant Escherichia coli: a novel isotropic optical fibre

<b>Background.</b> Orthopaedic oncological pelvic reconstructions have an elevated risk of infection with Gram-negative bacteria. This study evaluates the bactericidal ability of a novel antimicrobial blue light (ABL)-emitting optical fibre on antibiotic-sensitive <i>Escherichi coli</i> (AS-Ec) and ESBL-producing <i>E. coli</i> (ESBL-Ec). <b>Methods.</b> Time-to-kill assays used a 10 ml NaCl solution with a starting inoculum of 1×10⁵ c.f.u. ml^-1 for AS-Ec or ESBL-Ec; assays were repeated at least three times per strain. Experimental tubes had either one optical fibre [20.1 mW mm^-1; low power (LP)] or two optical fibres [40.3 mW mm^-1; high power (HP)], which delivered five wavelengths of ABL over 60 min. Control tubes had no optical fibres. Fifty microlitres of samples taken from each tube at 0, 10, 20, 30 and 60 min were streaked onto agar plates and incubated. c.f.u. ml^-1 was determined. Bactericidal reduction was defined as a 99.9% (≥3 log₁₀) reduction in c.f.u. ml^-1. One-way ANOVA was conducted. <b>Results.</b> Bactericidal effects were seen for AS-Ec under both LP-ABL and HP-ABL with a log₁₀c.f.u. ml^-1±sd difference of 3.44±0.35 (<i>P</i>=0.043) and 3.74±0.21 (<i>P</i>=0.048) at 30 and 20 min, respectively. For ESBL-Ec, while there was a significant reduction in bacterial colony formation, the bactericidal threshold was not reached with a log₁₀c.f.u. ml^-1±sd difference of only 1.02±0.41 (<i>P</i>=0.034) and 2.53±0.22 (<i>P</i>=0.037) at 60 min for LP-ABL and HP-ABL, respectively. <b>Conclusions.</b> A novel ABL-emitting optical fibre exhibited bactericidal effects in AS-Ec and a clinically meaningful reduction of ESBL-Ec, providing a promising avenue for the use of ABL as a potential therapy for Gram-negative infections.