In vitro evidence of antimicrobial synergy between Salvia chamelaeagnea and Leonotis leonurus

Extracts of the aerial parts of Salvia chamelaeagnea and L. leonurus were evaluated for the in vitro antibacterial activity when tested in combination against two Gram-positive bacteria ( Bacillus cereus and Staphylococcus aureus ) and two Gram-negative bacteria ( Escherichia coli and Klebsiella pneumoniae ) using the microdilution method. The minimum inhibitory concentration (MIC) were determined for the individual plant extract and also in combination using the fractional inhibitory concentration (FIC) and represented as data points in isobolograms. Individually, the plant extract showed good antibacterial activity against the four pathogens tested with the MIC values ≤ 3 mg mL − 1 . When the two extracts were combined, synergistic actions were observed against the Gram-positive bacteria while antagonism, synergism and/or additive actions were observed for the various ratios tested on the Gram-negative bacteria.