Enhanced photodynamic disruption of multidrug-resistant Acinetobacter baumannii biofilm using silver and zinc oxide nanostructures

<i>Acinetobacter baumannii</i> is a multidrug-resistant bacterium that frequently causes severe infections in hospital intensive care units. Considering the growing resistance of this pathogen, developing innovative strategies to combat it is essential. This study evaluated the efficacy of antimicrobial photodynamic inactivation (APDI) using Erythrosin B (EB) dye against this bacterium. The role of nanostructures in enhancing the effectiveness of this method was also investigated. The minimum inhibitory concentration of silver and zinc oxide nanostructures was determined against <i>A. baumannii</i> ATCC 19606 and <i>A. baumannii</i> 58ST strains. Then, APDI using EB and nanostructures was performed in the planktonic form. The effect of APDI on biofilm formation and eradication was investigated by crystal violet and colony counting methods. The impact of nanostructures on the uptake of EB by bacterial cells and their toxicity on L-929 cells was also evaluated. The results showed that EB uptake increased by 2.5-3 times in both strains in the presence of both nanostructures. APDI with EB alone did not affect the number of bacteria; however, a significant reduction in the number of bacteria was observed when EB was combined with nanostructures. This combination also showed significant inhibitory effects on biofilm formation and eradication. Nanostructures alone had a lower efficacy in inhibiting biofilm formation, but their addition to EB increased the lethal effect on biofilm. The possible mechanism of this effectiveness is the increase in the permeability of the bacterial cell membrane due to the presence of nanostructures, leading to more photosensitizer uptake and reactive oxygen species production.