Antibacterial activity of diazepam against planktonic and biofilm strains of methicillin-resistant Staphylococcus aureus.

The aim was to evaluate the antibacterial activity of diazepam against methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) strains of Staphylococcus aureus and its possible mechanism of action. The broth microdilution assay was used to determine the minimum inhibitory concentration (MIC) of diazepam. A checkerboard assay was used to evaluate the interaction of diazepam with different antibiotics. Colorimetric assays with MTT were used to evaluate the effect of diazepam against the biofilms by MSSA and MRSA. Flow cytometry and fluorescence microscopy were used to evaluate the possible mechanism of action of diazepam against MRSA. Diazepam had a MIC of 256 µg/mL. It only had indifferent interactions with the analyzed antibiotics. Diazepam significantly reduced the viability of MSSA and MRSA biofilms. Diazepam caused fragmentation of bacterial DNA and carbonylation of proteins, resulting in reduced cell viability. Therefore, diazepam has in vitro antimicrobial activity against planktonic and biofilm strains of MRSA and MSSA.