Antibacterial Synthetic Nanocelluloses Synergizing with a Metal-Chelating Agent

Abstract

Antibacterial materials composed of biodegradable and biocompatible constituents that are produced via eco-friendly synthetic strategies will become an attractive alternative to antibiotics to combat antibiotic-resistant bacteria. In this study, we demonstrated the antibacterial properties of nanosheet-shaped crystalline assemblies of enzymatically synthesized aminated cellulose oligomers (namely, surface-aminated synthetic nanocelluloses) and their synergy with a metal-chelating antibacterial agent, ethylenediaminetetraacetic acid (EDTA). Growth curves and colony counting assays revealed that the surface-aminated cellulose assemblies had an antibacterial effect against Gram-negative Escherichia coli (E. coli). The cationic assemblies appeared to destabilize the cell wall of E. coli through electrostatic interactions with anionic lipopolysaccharide (LPS) molecules on the outer membrane. The antibacterial properties were significantly enhanced by the concurrent use of EDTA, which potentially removed metal ions from LPS molecules, resulting in synergistic bactericidal effects. No antibacterial activity of the surface-aminated cellulose assemblies was observed against Gram-positive Staphylococcus aureus even in the presence of EDTA, further supporting the contribution of electrostatic interactions between the cationic assemblies and anionic LPS to the activity against Gram-negative bacteria. Analysis using quartz crystal microbalance with dissipation monitoring revealed the attractive interaction of the surface-aminated cellulose assembly with LPS Ra monolayers artificially produced on the device substrate.

Keywords: antibacterial cationic polymer; bactericidal activity; cellulose oligomer; crystalline assembly; ethylenediaminetetraacetic acid; synergistic effect.

Figure 1

Schematic illustration of this study. (a) Chemical structure of one-terminally aminated cellulose oligomers. (b) Antibacterial action of the surface-aminated cellulose assemblies with EDTA.

Figure 2

Time course of the optical densities of E. coli suspensions during incubation with and without surface-aminated and plain cellulose assemblies in the absence or presence of EDTA. The experiments were repeated three times, and the error bars correspond to the standard deviation.

Figure 3

Colony counting assays for E. coli suspensions after incubation with the surface-aminated or plain cellulose assemblies in the (a) absence and (b) presence of EDTA at different assembly concentrations for 48 h. The experiments were repeated three times, and the error bars correspond to the standard deviation.

Figure 4

Colony counting assays of E. coli suspensions after incubation with surface-aminated or plain cellulose assemblies at different EDTA concentrations. The experiments were repeated three times, and the error bars correspond to the standard deviation.

Figure 5

Fluorescence microcopy images of the mixed solutions of (a,b) the surface-aminated or (c,d) plain cellulose assemblies and E. coli in the presence (a,c) or absence (b,d) of EDTA after incubation for 48 h.

Figure 6

Changes in (a) Δf and (b) ΔD with respect to those of the intact monolayers after the LPS Ra monolayer was incubated with the dispersions of the surface-aminated cellulose assemblies for 2 h. Magenta symbols are the data collected in the EDTA-loaded buffer, while pink symbols are in the EDTA-free buffer.

Figure 7

Colony counting assays for S. aureus suspensions after incubation with the surface-aminated or plain cellulose assemblies in the presence of EDTA at different assembly concentrations for 48 h. The experiments were repeated three times, and the error bars correspond to the standard deviation.