Investigation of Anti-Biofilm and Quorum Sensing Inhibitory Properties of Isatin-Based Hydrazide Derivatives Against Klebsiella pneumoniae

Abstract

In this study, previously reported isatin-based hydrazide derivatives (5a–5i) were further evaluated for their anti-biofilm and quorum sensing (QS) inhibitory activities against Klebsiella pneumoniae and Chromobacterium violaceum CV026, respectively. The biofilm inhibition assay demonstrated that compound 5b, containing a 3-bromo substituent, exhibited the highest biofilm inhibition, reaching 84.19% at a concentration of 100 µg/100 µl. The significant efficacy of 5b is likely due to the enhanced electronic and steric properties conferred by the bromine atom, promoting stronger interactions with bacterial targets. Compound 5i, an unsubstituted benzene derivative, also showed substantial inhibition (86.10%), indicating that both substituted and unsubstituted aromatic rings influence biofilm formation.Further investigation of 5b’s anti-quorum sensing potential via a disc diffusion bioassay against C. violaceum CV026 revealed a concentration-dependent loss of violacein production, with the largest zone of pigmentation loss (21 mm) at 1 mg/ml. These findings suggest that 5b not only impairs biofilm formation but also disrupts QS signaling pathways. Molecular docking studies provided mechanistic insights into the interactions between the synthesized compounds and bacterial target proteins. The docking analysis revealed that hydrophobic interactions, including pi-pi and pi-alkyl stacking between the indolinone moiety of the isatin-hydrazide scaffold and key protein residues, played a crucial role in the inhibitory activity. Compound 5b exhibited the excellent binding affinity, further supporting its experimental potency.In conclusion, the experimental and computational data identify isatin-based hydrazide derivatives, particularly compound 5b, as promising candidates for the development of novel anti-biofilm and quorum sensing inhibitors, with potential applications in combating multidrug-resistant bacterial infections. These findings provide valuable insights into the structural features essential for antibacterial activity and lay the groundwork for future optimization of these compounds in therapeutic applications