Antibacterial Effects of Plant Extracts Activated by Photodynamic and Sonodynamic Therapy Against Pathogenic and Drug-Resistant Bacteria

The increasing prevalence of antibiotic-resistant microbes necessitates new antimicrobial strategies. In this study, the antibacterial activity of leaf extracts from a number of plants, Pistacia lentiscus, Laurus nobilis, Solanum lycopersicum, Ruta chalepensis, Inula viscosa, Myrtus communis, and Ficus carica, under photodynamic and sonodynamic activation was evaluated against S. aureus (methicillin-susceptible Staphylococcus aureus, MSSA), methicillin-resistant S. aureus (MRSA), and E. coli. Crude extracts of all the plants exhibited antibacterial activity against S. aureus, eradicating bacterial cells in 2–20 min. However, none of the extracts was active against E. coli. The most active extracts from P. lentiscus, L. nobilis, I. viscosa, and F. carica were tested against two clinical MRSA strains, and all inhibit cells within 5 to 40 min. These four active extracts were separated by reversed-phase chromatography, yielding fractions of varying polarity that exhibited dark activity (more hydrophilic fractions) or photodynamic properties (more hydrophobic fractions) when tested against S. aureus. Two extracts (from P. lentiscus and I. viscosa) exhibited sonodynamic activity against S. aureus, and only one (from P. lentiscus) against E. coli.