DEVELOPMENT OF CHITOSAN/COLISTIN NANO ANTIBIOTICS AND THEIR IN VITRO ACTIVITY AGAINST MULTIDRUG-RESISTANT ACINETOBACTER BAUMANNII

Abstract

Multidrug-resistant (MDR) Acinetobacter baumannii and Klebsiella pneumoniae cause serious hospital-acquired infections, for which colistin is often one of the final treatment options. However, its clinical utility is hindered by dose-related toxicity and resistance development. In this study, chitosan–colistin nanoparticles (CS–Col NPs) were fabricated using the ionic gelation technique as an alternative delivery platform for A. baumannii therapy. The particles were analyzed using dynamic light scattering (DLS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–visible spectroscopy. DLS revealed a hydrodynamic diameter of 245 nm with a polydispersity index of 0.26, whereas SEM imaging showed a dry-state diameter of 348 nm. The zeta potential of +25.6 mV indicated good colloidal stability. XRD patterns contained broad peaks at ~10° associated with chitosan and a sharp peak at ~29° attributed to crystalline colistin, suggesting a semi-crystalline composite structure. UV visible analysis showed a distinct absorption peak at ~298 nm with greater intensity than blank nanoparticles, confirming efficient drug loading. Antimicrobial assessment using broth microdilution revealed a minimum inhibitory concentration (MIC) of 0.25 µg/mL for CS–Col NPs, half that of free colistin, with a fractional inhibitory concentration (FIC) index of 0.5 indicating synergy. Compared with recent nanoparticle systems reported in the literature, the formulation achieved smaller particle size, narrower distribution, higher stability, and equal or superior antibacterial enhancement, highlighting its potential as a safer and more effective colistin delivery system.