Microscopic monitoring of the antibacterial potential of Nepeta elymaitica Bornm essential oil against kohlrabi leaves’ foodborne pathogens

Abstract

This study was conducted to investigate the antibacterial potential of the Nepeta elymaitica Bornm essential oil (Nepeta EO) against S. aureus and S. Typhi and evaluation its indirect applicability as a natural sanitizer in kohlrabi leaves. GC-MS analysis showed that Nepeta EO mainly contained 1,8-cineol, linalool, E-caryophyllene, and nepetalactone. Based on the results of time-killing assays, disc diffusion tests, and analysis of the released intracellular compounds Nepeta EO was more effective against S. aureus than S. Typhi. Furthermore, scanning electron microscopy images revealed that the cells of both pathogens significantly shriveled and were damaged by Nepeta EO. It is worth mentioning that the indirect application of Nepeta EO (8 mg/mL) in fresh kohlrabi leaves inoculated with pathogens effectively reduced S. aureus and S. Typhi by 4.09 and 5.44 log CFU/g, respectively. Moreover, the Nepeta EO resulted in maintaining the marketable characteristics of kohlrabi leaves, such as texture, color, and stability of chlorophyll content. These results indicated that Nepeta EO has a strong antibacterial ability, which can even indirectly kill both gram-positive and negative bacteria. It has a decent potential to be used as a novel and natural sanitizer in leafy vegetables without altering their quality and organoleptic properties.