Azithromycin and Tea Tree Oil Nanocapsules Coated With Chitosan: A New Strategy Against Resistant Pathogens

The problem of antimicrobial resistance has led to the study and development of new drug systems that combine natural compounds with classical antimicrobials. This study aimed to produce nanocapsules of Melaleuca alternifolia essential oil (TEO) and azithromycin (AZI) coated with chitosan (CH) with antimicrobial activity. The nanocapsule suspensions were prepared by the interfacial deposition method of a preformed polymer. They were then coated with CH solution at a 2% concentration. Physicochemical characterization included evaluation of pH, average hydrodynamic diameter (AHD), zeta potential (ZP), polydispersity index (PI), and morphological evaluation using Scanning Electron Microscopy (SEM). Biological tests performed included Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of free AZI and encapsulated AZI against resistant microorganisms: Staphylococcus aureus ATCC 33591, Klebsiella pneumoniae ATCC BAA2814, Enterococcus faecalis ATCC 51299, and Streptococcus sobrinus ATCC 27531. The average AHD of the nanocapsule suspension before CH coating (206.2 ± 2.2 nm) at 2% was lower than after coating (238.5 ± 1.7 nm), suggesting the formation of a thin CH layer around the nanocapsules. The PI values (0.173 ± 0.005 before and 0.245 ± 0.010 after) show that the suspension maintained its homogeneity in particle size and distribution even after coating. The ZP, which was negative (–28.66 ± 1.40 mV), became positive (+28.06 ± 1.10 mV) after coating. The pH became more acidic (4.38) due to the presence of CH in the suspension. SEM images after CH coating revealed the spherical/oval shape of the nanocapsules. MIC values for encapsulated AZI were lower than those for the free form of the drug for all tested bacteria after 24 hours. The nanocapsules proved to be a promising approach to combat infections caused by the bacterial species tested.