Inhibitory Effects of Essential Oils and Extracts of the Water-Steam Distillation Residues from Greek Herbs on Adherent Biofilm Formation by Common Pathogens

Biofilms pose a major challenge to the food industry, as they develop on both biotic and abiotic surfaces and contribute to the persistence of antibiotic-resistant pathogens. This study evaluated the antimicrobial and antibiofilm potential of Satureja thymbra, Thymus capitatus, and Origanum hirtum essential oils (EOs), their main components (thymol, carvacrol, p-cymene, and γ-terpinene), and ethanolic and ethyl acetate extracts of the water-steam distillation residue of T. capitatus (WSTRTc). Minimum Inhibition Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values of EOs and WSTRTc extracts ranged from 0.6 to 56.8 mg/mL. The corresponding MIC values of the main components ranged in lower values (0.5–2.4 mg/mL). Minimum Biofilm Inhibition Concentration (MBIC) and Minimum Biofilm Eradication Concentration (MBEC) were also determined. MBIC values for the EOs ranged from 0.6 to 4.7 mg/mL against biofilms of Escherichia coli, Listeria monocytogenes, Proteus mirabilis, and Salmonella Enteritidis. Significant antibiofilm activity at concentrations > 61 mg/mL and > 20 mg/mL was recorded by the ethanolic and ethyl acetate WSTRTc extracts, respectively, but no activity against L. monocytogenes and P. mirabilis biofilms was documented. These findings highlighted the efficacy of EOs and extracts derived from Greek herbs, suggesting their application in the food and pharmaceutical industry as natural antimicrobials and biofilm inhibitors.