In Vitro Antibacterial Activity and Combined Drug Sensitivity of 18 Lichen Species from Cangshan

This study aims to explore the in vitro antibacterial activity of 18 lichen species from Cangshan and the synergistic effect of their natural active products in combination with antibiotics against methicillin-resistant Staphylococcus aureus (MRSA). The in vitro antibacterial activity of 18 lichen species against 6 food-borne pathogens was determined using the agar well diffusion method, and the combined effect of active lichens and 7 common antibiotics was evaluated using the checkerboard method with MRSA as the tracer. Additionally, in vitro bactericidal curves, anti-mutagenic concentrations, and post-antibiotic effects were examined. The results demonstrated that 10 of the 18 lichen species exhibited in vitro anti-MRSA activity, with strongest antibacterial activity observed for Cetraria laevigata, showing extremely high sensitivity (the diameter of the inhibition zone was 22.0 mm). Furthermore, the combination of Lobaria kurokawae and Cladonia uncialis with piperacillin demonstrated a synergistic antibacterial effect, significantly reducing MRSA bacterial density (P<0.05), enhancing mutation prevention capability, and prolonging the post-antibiotic effect of piperacillin. These findings suggest that the extracts from various Cangshan lichen species exhibit promising antimicrobial activity against MRSA, and the combination of Lobaria kurokawae, Cladonia uncialis, and piperacillin shows a synergistic antibacterial effect, which have the potential for further development as antibiotics or antibiotic adjuvants.