Anti-Infective Effect of Anacardium occidentale L. Flowers Against Eskape Group Bacteria In Vitro, In Vivo, and In Silico.

BACKGROUND/OBJECTIVES: The study evaluated the in vitro antibacterial activity of the ethanolic extract of Anacardium occidentale flowers (EHAo) against ESKAPE pathogens and investigated the in vivo effects of the extract in Tenebrio molitor lethally infected with Staphylococcus aureus. In silico analyses investigated the affinity of compounds with sortase A.

METHODS: Chemical composition was characterized by HPLC and LC-MS. Antibacterial activity was determined by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and assays of adhesion and biofilm formation using S. aureus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, and clinical MRSA strains. In vivo toxicity and antimicrobial efficacy were assessed in T. molitor larvae infected with S. aureus (105 CFU/mL) and treated with PBS, ciprofloxacin (1.56 μg/mL), or EHAo (3.12-12.5 mg/mL). Molecular docking evaluated the interactions between the chemical compounds identified in EHAo and the sortase A active site.

RESULTS: EHAo contained shikimic acid, gallic acid, quercetin, isoquercetin, galloyl-glucose, digalloyl-glucose, and tetragalloylglucose isomers. The extract exhibited bactericidal activity (MIC 1.25-6.25 mg/mL), with the strongest effects against S. aureus, MRSA, and E. faecalis. EHAo inhibited adhesion and biofilm formation, except in K. pneumoniae. The extract showed low toxicity in vivo and was efficient in improving the larvae's survival following lethal infection with S. aureus. All compounds showed affinity to sortase A active site. However, digalloyl-glucose displayed the highest predicted affinity.

CONCLUSIONS: EHAo reduces bacterial virulence and improves survival in S. aureus-infected larvae, an activity probably related to the bactericidal activity, inhibition of adhesion and biofilm formation, and interaction with the sortase A active site.