From beta-cyclodextrin polyelectrolyte to layer-by-layer self-assembly microcapsules: From inhibition of bacterial growth to bactericidal effect

Abstract

Pathogenic bacteria resistance to antimicrobial agents has emerged as a major health issue. Developing new systems enabling inhibitory and bactericidal effects is crucial. Herein, layer-by-layer technique (LbL) was used to fabricate microcapsules composed of biopolymers, cationic polycyclodextrin (P(CD+)) and anionic alginate (alg−). This was achieved through successive adsorption of these polyelectrolytes onto calcium carbonate microparticles (CaCO3) used as template. Then, a chelating agent was added for removing the CaCO3 core, leading to microcapsules. Quartz crystal microbalance and zeta potential measurements evidenced the successful alternate adsorption of polyelectrolytes and related charge reversal, respectively, upon the LbL deposition. The shape of the capsules was characterized by Scanning Electron Microscopy (SEM) and fluorescence microscopy. The antibacterial activity of P(CD+) was first evidenced on two well-known bacteria: Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) using well diffusion method on Plate Count Agar (PCA) medium. Then, an inhibitory effect on the bacteria growth has been observed for the P(CD+)-based microcapsules during bacterial culture in Luria-Bertani (LB) broth medium. Our results pointed out towards a strong dependence of the extent of inhibition on the number of self-assembled polyelectrolytes' layers and capsules’ concentration. The effect increased with both concentration and number of layers. Acridine orange staining evidenced the bactericidal effect of P(CD+)-based microcapsules. This contribution demonstrates unambiguously that: i) aqueous solutions of P(CD+) exhibit antibacterial activity at physiological pH suggesting that P(CD+) can act as a versatile alternative to the widely studied chitosan whose antimicrobial activity is limited to acidic pH and ii) (P(CD+)/alg−)n hollow capsules can be exploited as an antibacterial agents with additional host properties.