The antimicrobial properties of 21 plant essential oils and two essences were investigated against five important food-borne pathogens, Campylobacter jejuni, Salmonella enteritidis, Escherichia coli, Staphylococcus aureus and Listeria monocytogenes. The oils of bay, cinnamon, clove and thyme were the most inhibitory, each having a bacteriostatic concentration of 0.075% or less against all five pathogens. In general, Gram-positive bacteria were more sensitive to inhibition by plant essential oils than the Gram-negative bacteria. Campylobacter jejuni was the most resistant of the bacteria investigated to plant essential oils, with only the oils of bay and thyme having a bacteriocidal concentration of less than 1%. At 35 degrees C, L. monocytogenes was extremely sensitive to the oil of nutmeg.
As powerful antibiotics lose their punch against “superbugs” such as vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA), scientists are searching for new antimicrobial agents from natural sources. Allicin, the major component of garlic, is one such agent, and it was recently shown to be potent against VRE and MRSA in two studies presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago in December.
A study conducted by Jaya Prakash and colleagues at the National University of Health Sciences in Lombard, IL, found that allicin has potent activity against VRE in vitro. “The basic problem with VRE is that it colonizes the gut,” says Prakash. “Many antibiotics used to control or prevent colonization also affect the normal flora.” The ideal solution, she explains, would be to prevent colonization with a food substance, given the safety of such compounds over antibiotics.