Influence of menthol on membrane-associated properties of tetracycline-resistant <i>Escherichia coli</i>

Abstract

<p>In this investigation, we assessed the antibacterial properties of menthol using <italic>Escherichia coli</italic> 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 µg/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 <italic>E. coli</italic> K12 and 40% in <italic>E. coli</italic> BN407.</p><p>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<sup>+</sup>-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.</p><p>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 <italic>E. coli</italic> strains.</p>

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