In vitro activity of plant extracts against biofilm-producing food-related bacteria

• Antibacterial, antibiofilm and antioxidant activities of methanolic extracts from five plants are reported.
• Strong antibacterial-antibiofilm activity against L. monocytogenes and S. aureus
• High polyphenol content and good antioxidant activity
• Active fractions contained myricetrin, quercitrin and apigenin 4′-O-β-glucoside.

The identification of effective antimicrobial agents also active on biofilms is a topic of crucial importance in food and industrial environment. For that purpose methanol extracts of Turkish plants, Ficus carica L., Juglans regia L., Olea europaea L., Punica granatum L. and Rhus coriaria L., were investigated. Among the extracts, P. granatum L. and R. coriaria L. showed the best antibacterial activity with minimum inhibitory concentrations (MIC) of 78–625 μg/ml for Listeria monocytogenes and Staphylococcus aureus and 312–1250 μg/ml for Escherichia coli and Pseudomonas aeruginosa. SubMICs produced a significant biofilm inhibition equal to 80–60% for L. monocytogenes and 90–80% for S. aureus. The extracts showed also the highest polyphenol content and the strongest antioxidant activity. Bioassay-guided and HPLC procedures demonstrated the presence of apigenin 4′-O-β-glucoside in P. granatum L. and myricetrin and quercitrin in R. coriaria L. Antigenotoxicity of plant extracts was also observed The present findings promote the value-adding of P. granatum L. and R. coriaria L. leaves as natural antimicrobial/antioxidant agents for control of food-related bacterial biofilms.