Experimental Evaluation of Antibacterial and Antibiofilm Activity of <i>Camellia sinensis</i>, <i>Fraxinus excelsior</i>, and Green Coffee Extracts Against <i>Pseudomonas aeruginosa</i>

Background: The excessive use of antibiotics has contributed to the emergence of antibiotic-resistant microbes, posing a significant global health concern. Additionally, the formation of biofilms by microorganisms on surfaces further exacerbates the problem by enhancing their resistance to antibacterial agents. Exploring alternative antimicrobial and antibiofilm agents that do not promote drug resistance is crucial to address these issues. This laboratory-based research investigated the antibacterial and antibiofilm efficacy of both water-based and alcohol-based extracts from three medicinal plants, namely, Camellia sinensis, Fraxinus excelsior, and green coffee, against Pseudomonas aeruginosa ATCC 27853 and an extensively drug-resistant (XDR) P. aeruginosa clinical isolate. Methods: Four distinct methodologies were employed to assess the antibacterial efficacy of the plant extracts, including spot assay, disc diffusion test, agar well diffusion technique, and the micro-broth dilution method. The antibiofilm potential was evaluated using the microtiter plate technique at the sub-inhibitory concentrations of each extract, only against P. aeruginosa ATCC 27853. Results: The findings revealed that C. sinensis extracts (both aqueous and ethanolic) were the most effective antimicrobials, displaying the lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration values. While F. excelsior exhibited intermediate antibacterial effects, the green coffee extract lacked substantial antimicrobial action. Furthermore, none of the plant extracts significantly inhibited biofilm formation by P. aeruginosa ATCC 27853. Conclusion: In general, C. sinensis demonstrated significant potential as an antibacterial agent and showed promising in vitro efficacy. However, the absence of significant biofilm inhibition and high MIC values for other extracts highlight the need for further formulation and mechanistic studies.