Effects of 462 nm Light-Emitting Diode on the Inactivation of Escherichia coli and a Multidrug-Resistant by Tetracycline Photoreaction

Abstract

The adaptability of bacterial resistance to antibiotics contributes to its high efficiency during evolution. Tetracycline (TC) is a broad-spectrum antimicrobial agent. Chromatographic analyses and mass spectrometry were used to study the effects of the light illumination of a 462 nm light-emitting diode (LED) on the conformational changes of TC in a phosphate buffer solution (PBS, pH 7.8). Especially, the inactivation of superoxide anion radicals (O₂•^-) and <i>Escherichia coli</i> (<i>E. coli</i>), including that of a multidrug-resistant <i>E. coli</i> (<i>MDR E. coli</i>), were investigated during the photolysis of TC. A photolysis product of TC (PPT) was generated in an alkaline solution after the illumination of a blue light. The mass spectra of PPT had characteristic ion signals in m/z 459, 445, and 249.1 Da. The PPT has the molecular formula of C₂₂H₂₂N₂O₉, and the exact mass is 458.44 g/mol. The inactivation of <i>MDR E. coli</i> is not significant with TC treatment. The drug-resistant ability of <i>MDR E. coli</i> has a less significant effect on PPT, and the changed conformation of TC retained the inactivation ability of <i>MDR E. coli</i> upon blue light photoreaction. With TC, illuminated by a blue light in a pH 7.8 PBS, O₂•^- was generated from TC photolysis, which enhanced the inactivation of <i>E. coli</i> and <i>MDR E. coli</i>. A 96.6% inactivation rate of <i>MDR E. coli</i> was reached with TC under 2.0 mW/cm² blue light illumination at 25 ± 3 °C for 120 min, and the effects of the TC-treated photoreaction on <i>MDR E. coli</i> viability repressed the growth of <i>MDR E. coli</i> by 4 to 5 logs. The present study of the blue light photoreaction of TC offers a new approach to the inactivation of <i>MDR E. coli.</i>