Antibacterial Activity of the Extracts Obtained from Rosmarinus officinalis, Origanum majorana, and Trigonella foenum-graecum on Highly Drug-Resistant Gram Negative Bacilli

Our aim was to determine the antimicrobial activity of three selected plants (Rosmarinus officinalis, Origanum majorana, and Trigonella foenum-graecum) against Extended Spectrum Beta Lactamase (ESBL)—producing Escherichia coli and Klebsiella pneumoniae— and to identify the specific plant fraction responsible for the antimicrobial activity. The plants were extracted with ethanol to yield the crude extract which was further subfractionated by different solvents to obtain the petroleum ether, the dichloromethane, the ethyl acetate, and the aqueous fractions. The Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal Concentrations (MBC) were determined using broth microdilution. The MICs ranged between 1.25 and 80 g/l. The majority of these microorganisms were inhibited by 80 and 40 g/l of the crude extracts. The petroleum ether fraction of Origanum majorana significantly inhibited 94% of the tested strains. Ethyl acetate extracts of all selected plants exhibited relatively low MICs and could be therefore described as strong antibacterial