In vitro evaluation the spectrum of antibacterial activity of botanical extracts and activity enhancement with outer membrane permeabilizers

Unique from Gram-positive bacteria, Gram-negative bacteria have an outer membrane containing lipopolysaccharide. This distinction has important implications for antibiotic therapies where this complex outer cell membrane presents a significant barrier to the entry of drugs, such as antibiotics, into the cell. Many botanical extracts are purported for their antibacterial properties. In this study, several botanical extracts were compared for their antibacterial activity against various Gram-positive and Gram-negative bacteria. Gram-positive bacteria were found to be more sensitive to the antibacterial effects of these botanical extracts, including Larrea tridentata, Eucalyptus glabra, Hypericum perforatum, Coptis chinensis and Hydrastis canadensis. For Gram-negative bacteria, various permeabilizers including EDTA, spermidine and polyethyleneimine, have been identified which facilitate the passage of the antibiotics through the outer membrane. These permeabilizers were tested to improve the efficacy of botanical extracts against Gram-negative bacteria where an increase in antibacterial activity was observed but was dependent on the type of permeabilizer used (EDTA being most effective) and the botanical extract (primarily observed with Larrea tridentata, Eucalyptus glabra, Coptis chinensis, and Salvia officinalis). These results characterize the spectrum of antibacterial activity of several commonly used botanical extracts in the presence and absence of membrane permeabilizers. The research performed supports the use of permeabilizers to potentially improve the antibacterial efficacy of botanical extracts and therapeutics.