Influence of menthol on membrane-associated properties of tetracycline-resistant Escherichia coli

In this investigation, we assessed the antibacterial properties of menthol using Escherichia coli strains, including a tetracycline-resistant (BN407) and a non-resistant reference (K12) strains. The disc-diffusion assay indicated remarkable antibacterial activity of menthol, warranting further exploration. The minimum inhibitory concentration (MIC) for menthol was determined to be 500 mu g/ml for both strains. Despite identical MIC values, menthol exhibited different effects on the colony- forming units (CFUs) of the strains, reducing CFUs by 55% in E. coli K12 and 40% in E. coli BN407. Growth kinetics studies revealed that menthol extended the Lag phase by 50% and decreased the specific growth rate and mean generation time by nearly 50% for both strains. These findings illustrate menthol's significant impact on bacterial replication and adaptation processes. Additionally, menthol disrupted membrane-associated properties, as evidenced by reduced H+ -flux through bacterial membranes, affecting both N,N-Dicyclohexylcarbodiimide (DCCD)-sensitive and non-sensitive proton flux rates. This indicates that menthol compromises the proton motive force critical for ATP synthesis and nutrient transport. In summary, menthol demonstrates potent antibacterial activity, influencing bacterial growth and survival. This activity is supposed to be due to the influence on membrane functionality. These effects are consistent across both tetracycline-resistant and non-resistant E. coli strains.