Plumbagin Disrupts Biofilm Integrity and Resistance Gene Expression in Carbapenem-Resistant <i>Acinetobacter baumannii</i>

Carbapenem-resistant <i>Acinetobacter baumannii</i> (CRAB) has appeared as a leading cause of hospital-acquired infections, resulting in high mortality rates and limited treatment options. The development of novel antibacterial agents has lagged behind the rapid spread of antibiotic-resistant bacteria; thus, alternative therapeutic strategies are urgently needed. In this study, we investigated plumbagin, a natural compound derived from <i>Plumbago zeylanica</i> L., for its potential antibacterial and antibiofilm activities against CRAB. MIC and MBC determinations showed that plumbagin significantly inhibited growth and exerted bactericidal activity at low concentrations. Biofilm inhibition concentration and biofilm eradication concentration assays revealed that plumbagin both prevented biofilm formation and eradicated mature biofilms. Consistent with these findings, XTT reduction assays showed a marked decrease in metabolic activity after plumbagin treatment, and confocal laser scanning microscopy with COMSTAT analysis confirmed reduced biofilm biomass and decreased viability of biofilm-embedded cells. Further, quantitative polymerase chain reaction confirmed the downregulation of the carbapenem-resistance gene <i>bla</i>_OXA-23 and biofilm-related genes, including <i>bfmR</i>, <i>csuA/B</i>, <i>ompA</i>, and <i>bap</i>. Collectively, these results reveal plumbagin as a therapeutic candidate against CRAB.