The effect of Spearmint, Oregano, and Thyme extracts on biofilm formation by Listeria monocytogenes, Escherichia coli O157: H7, and Salmonella typhimurium.

The formation of bacterial biofilm on surfaces associated with food processing is of particular concern. Due to the health concerns associated with the production of biofilm on food-related surfaces and the increase in antimicrobial resistance in pathogenic bacteria, the present study aimed to investigate the anti-biofilm effects of oregano, spearmint, and thyme extracts against biofilms of <i>Listeria monocytogenes</i>, <i>Escherichia coli</i> O157: H7, and <i>Salmonella typhimurium</i>. Spearmint, oregano, and thyme plants were freshly prepared, dried, and ground. The aqueous and ethanolic extracts of the plants were extracted by soaking. The amount of phenolic compound of the aqueous and ethanolic extracts was evaluated by spectrophotometric method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts were determined. The biofilm inhibition and destruction by the extracts were studied using the microdilution method. The results showed that the highest amount of phenolic compounds among ethanolic and aqueous extracts belonged to oregano and thyme extracts, respectively. The results also showed that the lowest effective concentration of the extracts on L. monocytogenes was by thyme aqueous extract with MIC and MBC of 1.8 and 2%, respectively, and for oregano ethanolic extract was 1.2 and 1.4%. The most significant biofilm inhibitory effect on <i>L. monocytogenes</i>, <i>S. typhimurium</i>, and <i>E. coli</i> O157: H7 was observed for thyme aqueous extract and oregano ethanolic extract. The results of the present study indicate that aqueous and ethanolic extracts of spearmint, oregano, and thyme plants have inhibitory and disruptive effects on biofilm formation by pathogenic bacteria. Therefore, these natural antimicrobial compounds can be used to control and prevent biofilm formation in the food industry.