GC–MS Characterization and Biological Evaluation of Costus speciosus Rhizomes: Antibacterial Activity against MDR and XDR Bacteria, Ultrastructural and Morphological Alterations, and Anticancer Potential

Abstract The rapid emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) bacteria represents a major global health challenge, necessitating the exploration of novel antimicrobial agents from natural sources. This study investigated the antibacterial potential Costus speciosus rhizome extracts and evaluated the cytotoxic activity of the most active fraction. A total of 29 bacterial isolates obtained from clinical specimens and meat products were subjected to antimicrobial susceptibility testing (AST) to determine their resistance profiles. Based on the observed resistance patterns, 11 representative MDR/XDR isolates, including Staphylococcus aureus (n = 18), Escherichia coli (n = 8), Klebsiella pneumoniae (n = 1), Serratia rubbidea (n = 1), and Hafnia alvei (n = 1), were selected for further investigation. Rhizome extracts were prepared using ethanol, methanol, ethyl acetate, and cold water, and their antibacterial activities were initially screened using the agar well diffusion assay. The ethyl acetate extract showed the strongest antibacterial activity and was subsequently fractionated using column chromatography, yielding 43 fractions. The fractions were screened for antibacterial activity, and nine fractions exhibited activity, with fraction 4 showing the strongest antibacterial effect. The MIC and MBC values of the active fraction ranged from 0.063 − 0.250 mg/mL each, respectively. Gas chromatography–mass spectrometry (GC–MS) analysis of fraction 4 identified 3 major compounds, including azuleno[4,5-b]furan-2(3H)-one (65.87%), dihydrodehydrocostus lactone (10.54%), and (Z,Z,Z)-1,8,11,14-heptadecatetraene (9.91%). Transmission electron microscopy (TEM) revealed severe ultrastructural alterations in treated bacterial cells, including cell wall disruption and cytoplasmic leakage. The cytotoxic activity of the most active fraction was subsequently evaluated against HepG2, A-549, and WI-38 cell lines. The fraction demonstrated potent cytotoxic activity against HepG2 and A-549 cells, with IC 50 values of 5.17 ± 0.49 and 8.27 ± 0.61 µg/mL, respectively, while the CC 50 value against WI-38 cells was 23.92 ± 0 .86 µg/ml, yielding selectivity indices (SI) of 4.63 and 2.89, respectively. In conclusion, the active fraction of Costus speciosus rhizome represents a promising source of antibacterial and anticancer agents against drug-resistant pathogens.