Antibacterial activity of bioactive anthraquinones isolated from Cassia tora L. against pathogenic intestinal microorganisms

Abstract

Antimicrobial resistance (AMR) poses a major global health challenge, particularly in intestinal infections where the efficacy of conventional antibiotics is rapidly declining. The rising prevalence of antibiotic-resistant pathogens underscores the urgent need for alternative antimicrobial agents with favorable activity profiles. This study evaluated the antibacterial potential of bioactive anthraquinones isolated from Cassia tora L. seeds against clinically relevant intestinal pathogens and probiotic bacteria. Five key anthraquinones, rhein, physcion, anthraquinone-2-carboxylic acid, emodin, and aloe-emodin, were identified and tested for their antibacterial activity. The anthraquinone metabolites exhibited strong antibacterial activity against pathogenic bacteria (Escherichia coli, Staphylococcus aureus, Clostridium difficile, etc.), while showing moderate to relatively lower inhibitory effects against beneficial probiotic strains such as Clostridium butyricum, Bifidobacterium bifidum, and Lactobacillus casei. The MIC profiles indicate relative or modest selectivity toward pathogens, rather than a complete sparing of probiotic species. Molecular docking analysis revealed that these metabolites bind favorably to key bacterial resistance proteins, often surpassing ciprofloxacin in binding affinity, supporting their observed antibacterial activity. Together, these results suggest that C. tora anthraquinones preferentially inhibit intestinal pathogens, maintaining a comparative margin of safety for beneficial gut flora. Anthraquinones isolated from C. tora seeds exhibit potent antibacterial activity toward pathogenic intestinal bacteria and relatively reduced activity against probiotic strains, reflecting selective preference in intestinal bacteria. These findings support their potential as natural antimicrobial candidates for managing intestinal infections and contributing to AMR mitigation. Nonetheless, the measurable inhibitory effects on probiotic species emphasize the need for careful dose optimization and microbiome-conscious therapeutic strategies. Further studies focusing on the mechanism of action, pharmacokinetics, toxicity, and in vivo efficacy are required to evaluate their clinical applicability.