Abstract
The aim of this study was to evaluate the antibacterial and antibio-film potential of two naturally occurring naphthoquinones, 2-hydroxy-1,4-naphthoquinone (2-HNQ) and 2-methoxy-1,4-naphthoquinone (2-MNQ), against the Gram-negative bacterium Escherichia coli strain ATCC 25922. In the first step of the study, the minimum inhibitory concentrations (MICs) of 2-HNQ and 2-MNQ were determined using the microdilution method. Subsequently, possible mechanisms underlying the antibacterial activity of 2-HNQ and 2-MNQ against E. coli were investigated by assessing intracellular reactive oxygen species (ROS) production and membrane permeability. Finally, the impact of 2-HNQ and 2-MNQ on swarming motility and on pre- and post-biofilm formation of E. coli was evaluated. The MIC of 2-HNQ against E. coli was 500 µg mL–1, while that of 2-MNQ was 100 µg mL–1. Both compounds increased intracellular ROS production and altered the membrane permeability of E. coli. Moreover, 2-HNQ and 2-MNQ reduced swarming motility and inhibited both pre- and post-biofilm formation. The results of this study indicate that both naphthoquinones possess antibacterial potential, with 2-MNQ showing greater potency against E. coli. Their antibacterial activity appears to involve ROS generation and disruption of membrane permeability. Importantly, both tested naphthoquinones also impaired E. coli motility and bio-film formation, suggesting potential applications in the treatment of infections caused by E. coli.