The emergence of antibiotic resistance has led to the search for novel strategies that can overcome this issue. In this connection,

the plant secondary metabolites play a crucial role in combating the resistance. This study was undertaken with an aim to assess the resistance modulating potential of berberine as efflux pump inhibitor against quinolone resistant S. aureus isolates from bovine mastitis. The antibacterial activity of berberine was evaluated using broth microdilution assay. The interaction of berberine with the antibiotics under study was assessed by checkerboard assay. The resistance modulating potential of berberine was appraised by real time quantitative PCR. The broth microdilution assay revealed that berberine has a weak antibacterial activity. When used in combination with quinolone antibiotics, berberine could lower the MICs of the antibiotics. The relative gene expression study pointed out that berberine act as an efflux pump inhibitor down regulating the expression of norA and norC efflux pump genes. The study concluded that plant metabolites can be used as potential candidates in reversing the antimicrobial resistance.

Highlights

• Berberine is found to have weak antimicrobial activity.
• Berberine reduced the MIC of resistant quinolones when combined with quinolone antibiotics against S. aureus.
• Berberine could downregulate the mRNA expression of nor efflux pump genes, thereby overcoming antibiotic resistance.