Antibacterial and Antibiofilm Activities of Thailand Propolis Against Escherichia coli

Escherichia coli is an important bacterium for preventing food poisoning and biofilm infections. The emergence of antibiotic-resistant microorganisms necessitates the development of new antibiotics. The formation of bacterial biofilm is a drug-resistance mechanism utilized by diverse microorganisms. Therefore, it is important to identify compounds that can inhibit biofilm formation and cell survival, without triggering drug resistance. Herein, the antibacterial and antibiofilm activities of 2 types of Thai propolis (collected from Chiang Mai and Chanthaburi) against E. coli were investigated. The antibacterial activity was evaluated using the paper-disc method, while the minimum inhibitory concentration assay was performed using 2-fold serial dilution. Both types of Thai propolis and their isolated compounds showed antibacterial activity against E. coli (minimum inhibitory concentration: 32 µg/mL). The biofilm growth and development were assessed using a crystal violet solution. In particular, the extracts of the Chiang Mai propolis exhibited a significant antibiofilm formation activity against E. coli. Four prenylflavonoids, present in high proportions in the Chiang Mai propolis extracts, inhibited biofilm formation at low concentrations, contributing to the overall antibiofilm activity. These findings indicate that Thai propolis, a natural product, exhibits antibacterial and antibiofilm activities against E. coli.