This research mainly focuses on the preparation of chitosan-alginate Nanoparticle by ionotropic gelation method using calcium chloride and sodium alginate to form nanocomposites of CH-ALg, examine their antibacterial activity against multidrug resistance (MDR) bacteria, and evaluate the stability of chitosan-alginate formula in different biological fluids, including simulated gastric fluid (SGF) and intestinal fluid (SIF). The average diameter of particles size prepared was measured by an Atomic force microscope (AFM) and it was 61.91 nm. Otherwise, the nature of functional groups present in CH-ALg nanoparticle was investigated by Fourier transforms infrared (FTIR) analysis. The stability of synthesized CH-ALg nanoparticle was measured by Zeta potential measurement and show high stability with a 79 mV ratio. The SEM picture shows that particles are shown to be in the form of bundles and the size of nanoparticles was in the range of (14-84nm). The antibacterial activity of CH-ALg was tested against (MDR) Gram-positive bacteria (staphylococcus aureus) and Gram-negative bacteria (Salmonella typhi, Pseudomonas aeruginosa, and Enterobacter cloacae). The results exhibited a significant impact of antibacterial action against isolates of MDR. CH-ALg nanoparticles were loaded with antibiotic doxycycline in order to strengthen the antibacterial action and drug delivery effectiveness. The synergistic effects of prepared CH-ALg loaded with DOX antibiotic at several concentrations toward MDR bacteria were also examined. The results indicate that DOX-loaded nanoparticles have a significant improvement for antibacterial activity against Gram-negative and Gram-positive compared to doxycycline alone. The formula of chitosan- alginate was stabile in various biological fluids including simulated gastric fluid (SGF) and simulated intestinal fluid (SiF)
