The role of chitosan in enhancing the solubility and antibacterial activity of emodin against drug-resistant bacteria

Similar to most anthraquinone compounds, the pharmacological properties of emodin are limited because of its low water solubility. In this study, the formulation of chitosan and emodin (EMD/CS) was prepared by a bottom-up method with precipitation and sonication steps in order to enhance the solubility of emodin. Thanks to the interactions of oxygen-and nitrogen-containing groups in chitosan with emodin molecules, the solubility of emodin in the formulation was remarkably increased to 0.5 mg/mL. The EMD/CS particles were well dispersed and distributed in a range of sub-micrometer with an average particle size of 342 nm. The EMD/CS formulation exhibited synergic antibacterial activity of emodin and chitosan, against drug-resistant bacterial strains, namely Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) and <i>Escherichia coli</i> O157:H7 (<i>E. coli</i> O157:H7). When the compositions of emodin and chitosan increased, the antibacterial effectiveness of the EMD/CS formulation increased. The EMD/CS formulation with compositions of 0.5 mg/mL of emodin and 9.0 mg/mL of chitosan could significantly inhibit the proliferation of <i>E. coli</i> O157:H7. Meanwhile, the EMD/CS formulation with a lower concentration of emodin (0.4 mg/mL) and chitosan (7.2 mg/mL) could cause an extermination effect on MRSA. The enhanced solubility of EMD/CS formulation suggests that this formulation can be a potential candidate for the treatment of infectious diseases caused by drug-resistant bacterial pathogens.