Disruption of bacterial membranes by plant extracts of celandine and dandelion: microbiological and langmuir monolayer studies

Abstract

The article presents a study on the disruption of the bacterial membrane by celandine (CME) and dandelion (TOE) extracts containing bioactive compounds responsible for their antibacterial activity. The in vitro microbiological tests showed antibacterial effect both on Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) pathogenic bacteria species. However, in the case of celandine herb extract, the effect was stronger, especially for Gram-positive bacteria. For a deeper understanding of the mechanism of antibacterial action, both studied extracts were subjected to biophysical studies on artificial bacterial lipid membranes, modeled with the Langmuir monolayers technique. The monolayer investigations were performed using two approaches: (i) monitoring the penetration of extracts injected into the aqueous subphase beneath a compressed lipid film, and (ii) comparing surface pressure–area isotherms recorded on a subphase with and without addition of extracts. These experiments confirmed the activity of TOE and CME at the membrane level, demonstrating the penetration of extract components into the membranes and their fluidizing effect. AFM analysis of the domain structures of the films transferred onto solid supports (Langmuir-Blodgett) revealed differences in film topography induced by the extracts and are in a good agreement with the results of biological tests and analytical analyses of the tested extracts. These findings confirm that the stronger antibacterial effect of CME, associated with a higher content of bioactive compounds, exerts a more destructive effect on the bacterial lipid membranes compared to TOE.