Effect of structure on the interactions between five natural antimicrobial compounds and phospholipids of bacterial cell membrane on model monolayers.

In vitro biophysical study using Langmuir monolayers to analyze interactions between antimicrobial compounds and bacterial phospholipids.

“Monolayers composed of bacterial phospholipids were used as model membranes to study interactions of the naturally occurring phenolic compounds 2,5-dihydroxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde, and the plant essential oil compounds carvacrol, cinnamaldehyde, and geraniol”

Five natural compounds (2,5-dihydroxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, carvacrol, cinnamaldehyde, geraniol) and three bacterial phospholipids (DPPE, DPPG, cardiolipin).

“The lipid monolayers consist of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1,2-dihexa- decanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), and 1,1',2,2'-tetratetradecanoyl cardiolipin (cardiolipin).”

Experiments were repeated twice for each condition.

“Experiment was repeated twice.”

Not specified; measurements were taken after a 10-minute equilibrium period and during compression.

“After a 10 min equilibrium to ensure evaporation of solvent, film compression was started by moving the two barriers symmetrically.”

The compounds modified lipid monolayer structures by integrating into the monolayer, forming aggregates, reducing packing effectiveness, increasing fluidity, and altering the total dipole moment.

“Results of the study indicated that the five compounds modified the three lipid monolayer structures by integrating into the monolayer, forming aggregates of antimicrobial –lipid complexes, reducing the packing effectiveness of the lipids, increasing the membrane fluidity, and altering the total dipole moment in the monolayer membrane model.”

Interactions depended on both the structure of the antimicrobials and the composition of the monolayers.

“The interactions of the five antimicrobial compounds with bacterial phospholipids depended on both the structure of the antimicrobials and the composition of the monolayers.”

Cinnamaldehyde and geraniol induced the biggest reduction of surface potential in all three monolayers.

“Cinnamaldehyde and geraniol induced the biggest reduction of surface potential in all three monolayers which could be ascribed by the strong hydrophobic attraction between the aromatic part or hydrocarbon chain of the compounds and the phospholipid acyl chains”

The study uses monolayers as model membranes rather than biological bilayers, and the exact molecular mechanisms in living cells are not readily defined by these experiments alone.

“Although the biological membrane is a bilayer, it is believed that many important phenomena which take place in bilayer membrane can be elucidated by experiments on the monolayer at an interface”