Effect of structure on the interactions between five natural antimicrobial compounds and phospholipids of bacterial cell membrane on model monolayers
Monolayers made of bacterial phospholipids were used as model membranes to investigate the interactions of naturally occurring phenolic compounds 2,5-dihydroxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde, as well as plant essential oil compounds carvacrol, cinnamaldehyde, and geraniol. These compounds were previously found to be active against both Gram-positive and Gram-negative pathogenic microorganisms. The lipid monolayers consisted of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1,2-dihexadecanoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DPPG), and 1,1′,2,2′-tetratetradecanoyl cardiolipin (cardiolipin). Surface pressure-area (π-A) and surface potential-area (Δψ-A) isotherms were measured to assess changes in the thermodynamic and physical properties of the lipid monolayers.
The study results showed that all five compounds altered the lipid monolayer structures by integrating into the monolayer, forming aggregates of antimicrobial-lipid complexes. These interactions reduced the packing efficiency of the lipids, increased membrane fluidity, and modified the overall dipole moment in the monolayer model. The extent of these effects depended on both the structure of the antimicrobial compounds and the composition of the lipid monolayers. The experimental findings provide valuable insight into the molecular interactions between naturally occurring antimicrobial compounds and the phospholipids of bacterial cell membranes, shedding light on the mechanisms behind their antimicrobial activity.