LC-MS/MS profiling and evaluation of antibacterial and antibiofilm activities of Conocarpus lancifolius phenolics against Acinetobacter baumannii

Acinetobacter baumannii is a clinically significant pathogenic bacterium known for its ability to form biofilms. Few studies have comprehensively investigated the chemical composition of Conocarpus lancifolius growing in Saudi Arabia. Here, we investigated the LC-MS/MS (liquid chromatography-tandem mass spectrometry) chemical profile of the Conocarpus lancifolius extract and evaluated its antibacterial activity along with that of eight key identified phenolic compounds. Flavonoids, chalcones, phenolic acids, triterpenoids and fatty acids were identified as the major phytochemical classes, with flavonoids such as gallocatechin, epigallocatechin-3- O -gallate (EGCG), myricetin, quercetin, and kaempferol, as well as several sulfated derivatives, as key constituents. All tested samples exhibited antibacterial activity, producing clear inhibition zones around the wells except for dihydromyricetin. The leaf extract, gallic acid, gallocatechin, and quercetin-3- O -glucoside exhibited weak antibacterial potential (MIC 512-1024 µg/mL), whereas EGCG, myricetin, and syringetin-3- O -glucoside displayed moderate activity (MIC values of 32-128 µg/mL). Notably, catechin exhibited strong activity (MIC 4-16 µg/mL) against the investigated Acinetobacter baumannii clinical isolates. Also, the antibiofilm potential of the tested compounds was assessed using the crystal violet assay. Only catechin exhibited antibiofilm action at 0.5 MIC values and decreased the ratio of strong and moderate biofilm-forming bacterial isolates from 63.16% to 21.05%. Molecular investigation via quantitative real-time PCR (qRT-PCR) showed that catechin suppressed the transcription of major biofilm-associated genes ( csuE , ompA , and bap ) in the biofilm-forming Acinetobacter baumannii. Molecular docking was employed to elucidate the binding interactions of the tested phytochemicals with two key biofilm-related targets of Acinetobacter baumannii , CsuE and OmpA. Catechin exhibited the most stable binding to both targets, characterized by low root mean square deviation (RMSD) values and consistent interactions, despite not having the top docking scores. In contrast, glycosylated flavonoids and EGCG showed less stable binding poses. These results provide structural support for the superior experimental antibiofilm activity of catechin. Thus, we can conclude that the polyphenolic constituents of Conocarpus lancifolius exhibited potential antibacterial and antibiofilm activities, with catechin being one of the active contributors alongside other active phenolics.