Effects of Graphene Derivatives and Near-Infrared Laser Irradiation on E. coli Biofilms and Stress Response Gene Expression

Photothermal therapy combines the effects of near-infrared laser (NIR laser) and strong light-absorbing materials to combat pathogens and unwanted biofilms. Graphene derivatives have a negative effect on microorganisms, and the combination of NIR laser irradiation and carbon nanomaterials (CNMs) can enhance their antibacterial effect. This investigation is devoted to the determination of the expression level of bacterial stress response genes (<i>soxS</i> and <i>rpoS</i>) under graphene oxide (GO), reduced graphene oxide (rGO), and NIR laser irradiation (1270 nm). GO, rGO and NIR laser irradiation separately and irradiation in the presence of graphene derivatives cause an increase in the expression level of <i>rpoS</i> associated with the general stress response of bacteria. GO and rGO do not change the expression level of <i>soxS</i> associated with the cell response to oxidative stress, and decrease it in the presence of a strong oxidizing agent paraquat (PQ). The expression of <i>soxS</i> increases under laser irradiation, but decreases under NIR laser irradiation in combination with graphene derivatives. The effect of GO, rGO, and NIR laser irradiation on the formation and eradication of <i>E. coli</i> biofilms was studied. NIR laser with GO and rGO suppresses the metabolic rate and decreases the intracellular ATP content by 94 and 99.6%, respectively. CNMs are shown to reduce biofilm biomass and the content of extracellular polymeric substances (EPSs), both exopolysaccharides and protein in the biofilm matrix. Graphene derivatives in combination with NIR laser irradiation may be an effective means of combating emerging and mature biofilms of Gram-negative bacteria.