Quinic acid enhances kanamycin efficacy against methicillin-resistant Staphylococcus aureus biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) form biofilms that contribute to increased antimicrobial resistance, leading to treatment failure and/or relapse. It is, therefore, necessary to develop new antibiofilm strategies to eradicate MRSA biofilms related infections. This study was aimed to evaluate the effect of the combination of quinic acid and kanamycin against the preformed biofilms of methicillin-resistant Staphylococcus aureus.

Broth microdilution method was deployed to evaluate the antibacterial activity. Whereas antibiofilm activity was evaluated by crystal violet staining, 3-(4, 5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium-bromide (MTT) assay, and scanning electron microscopy (SEM). The checkerboard method was adopted to assess the combination effects. Quantification of exopolysaccharides was determined by the phenol-sulfuric acid method. The eDNA was quantified by fluorescence spectrophotometry. Cytotoxicity activity was evaluated by the MTT assay on the human embryonic kidney (HEK 293) cell line.

Quinic acid, combined with kanamycin, effectively eradicated the methicillin-resistant S. aureus biofilms by effecting biofilm biomass and cell viability. Scanning electron microscopy demonstrated a less adherence of S. aureus cells, - after treatment with quinic acid combined with kanamycin, as compared to each drug alone. The combination of quinic acid and kanamycin thus demonstrated the ability to destroy the exopolysaccharides and eDNA of biofilm matrix without any toxic effect on HEK 293 cells.

Our results demonstrated the potential of using quinic acid in combination therapy, with an antibiotic, against infections caused by MRSA strains.