Antimicrobial effects of naturally occurring compounds against microorganisms relevant to food safety
Different types of antibiotics and chemical preservatives have been widely used in the agricultural food industry for various purposes including improvement of productivity and profits in modem farming practice, control of animal diseases and extension of shelflife of food products. However, due to increasing public concerns on the potential harmful effect posed by antibiotic residues in foods and the development of antibiotic resistance as a result of extensive use of chemical antibiotics in agriculture, the European Commission has banned the growth promoting antimicrobials in food animal production since Jan 2006. Research on the potential application of naturally occurring compounds in the food industry has recently gained increasing attention. This study aim at evaluating the antimicrobial effects of naturally occurring compounds against pathogenic microorganisms relevant to food safety, public health, animal health and welfare. The overall objectives included the determination of the minimum inhibitory concentrations of the active compounds, investigation of the possible synergistic effects when combining different natural antimicrobial compounds and the investigation of antimicrobial modes of action of these active compounds. Antibacterial activities of naturally-occurring compounds were evaluated against Escherichia, coli (E. coli), Clostridium sporogenes and Mycobacterium avium subspecies paratuberculosis {Map). The most active compounds against these bacteriainclude 2,5-dihydroxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, apple Epolyphenols, green tea polyphenols, gallic acid, garlic powder, onion powder, onion oil,carvacrol, oregano oil, tra«5-cinnamaldehyde and cinnamon oil. These compounds were subjected to antimicrobial mode of action studies. Significant cellular responses e.g. leakage of phosphate and reduction of intracellular ATP wereobserved. Monolayer study, a biophysical approach, suggested that the compounds interacted with cell membrane lipids, which was in agreement with the major findings of this study obtained using the biological approaches. A partial synergistic effect against vM. smegmatis MC2155 was also observed when combining oregano oil and herbal extract Aw at sub-MIC concentrations.
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