The biological role played by essential oils extracted from aromatic plants is progressively being recognized. This study evaluated the potential antibacterial activity of ten essential oils againstChromobacterium violaceum,Pseudomonas aeruginosa, andEnterococcus faecalisby measuring their minimum inhibitory concentration. We found that essential oils exert different antimicrobial effects, withOriganum vulgareandFoeniculum vulgaredemonstrating the most significant inhibitory effect on bacterial growth forC. violaceumandE. faecalis. The growth ofP. aeruginosawas not affected by any essential oil concentration we used. Sub-inhibitory concentrations of essential oils reduced inC. violaceumandE. faecalisbiofilm formation, violacein amount, and gelatinase activity, all of which are biomarkers of the Quorum Sensing process. These concentrations significantly affect the global methylation profiles of cytosines and adenines, thus leading to the hypothesis that the oils also exert their effects through epigenetic changes. Considering the results obtained, it is possible that essential oils can find a broad spectrum of applications in counteracting microbial contamination and preserving sterility of surfaces and foods, as well as inhibiting microbial growth of pathogens, alone or in combination with traditional antibiotics.