Antibacterial and Antibiofilm Potency of Menadione Against Multidrug-Resistant S. aureus

Menadione is an analogue of 1,4-naphthoquinone (1,4-NQ) that possesses enormous pharmaceutical potential. The minimum inhibitory concentration (MIC) of menadione was determined against eighteen pathogens of the ESKAPE category, including thirteen multidrug-resistant (MDR) and five standard strains. From a total of eighteen pathogens, five strains of S. aureus (four: MDR and one: Standard strain) were considered further for detailed studies. This study included the determination of minimum bactericidal concentration (MBC), time-kill assay, scanning electron microscopic technique (SEM), and detection of reactive oxygen species (ROS). Additionally, the effect of menadione on biofilms of three strains of S. aureus was performed through crystal violet assay, SEM, and confocal laser scanning microscopy (CLSM). Menadione exerted substantial antibacterial activity against S. aureus (S8, S9, NCIM 5021) at a lower MIC (64 µg/mL). Whereas, the MIC of 256 µg/mL was displayed against J2 and J4 (MDR and biofilm-forming strains). The time-killing effect of menadione against S. aureus strains was observed after 9 h at MBCs of 64 µg/mL (NCIM 5021), 128 µg/mL (S8, S9), and 512 µg/mL (J2, J4). Enhanced levels of ROS in all five S. aureus were observed in presence of menadione (MICs and MBCs). The relation of enhanced ROS due to menadione activity invigorated us to explore its effect on S. aureus biofilms. We report menadione-mediated inhibition (> 90%) of biofilm formation (at respective MICs) and effect on preformed biofilms (> 85%) at 1024 µg/mL. Menadione possessing antibacterial and antibiofilm potentials are imperative in the era of multidrug resistance developed by bacterial pathogens.