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Abstract
The emergence of multidrug resistant (MDR) pathogens has drawn attention to natural antimicrobial compounds, such as essential oils (EOs)
The aim of the present study was to investigate the inhibitory activity of three EOs against 15 Salmonella strains resistant to 16 commonly used antimicrobials. EOs of O. vulgare, T. serpyllum, and T. vulgariswere tested in triplicate for 15 bacterial strain by Kirby-Bauer disk diffusion method and broth microdilution method to determine the minimal inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC), according to the Clinical and Laboratory Standards Institute guidelines with minor modifications.
O. vulgare and T. serpyllum showed high antimicrobial activity compared to T. vulgaris in all tested antibiotic-resistant strains (P-value <0.01). The mean diameter of the bacterial growth inhibition zone was 18.7 mm for O. vulgaris, 19.2 mm for T. serpyllum, and 14.2 mm for T. vulgaris. The MIC and MBC mean values of O. vulgare were respectively 0.037% and 0.058%, for T. serpyllum 0.036% and 0.041%, for T. vulgaris 0.13% and 0.15%. All strains resulted resistant totrimethoprim-sulamethoxazoleand 14 strains resulted resistant to tetracycline, considered a highly important antimicrobial. Among Salmonella serovars tested the monophasic S. Typhimurium has exhibited the highest antimicrobial resistance to synthetic molecules while they were sensitive to EOs.
The EOs of O. vulgare and T. serpyllum, which contain carvacrol as the main constituent, showed the greatest antimicrobial effect against MDR Salmonella strains.
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