Antibacterial activity of chemically versus enzymatic functionalized wool with ɛ-poly-L-lysine

The effect of the coupling approach (chemical by using carbodiimide chemistry and grafting-to versus grafting-from synthesis routes, and enzymatic by using transglutaminase) of ɛ-poly-L-lysine (ɛPL) graft yield with wool fibers was studied and evaluated related to their antibacterial activity against gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria, after 1–24 h of exposure. While the ɛPL applied was evaluated colorimetrically by wool staining with two acid dyes and quantitatively by evaluation of the basic groups using potentiometric titration, its orientation was determined by Fourier transform infrared spectroscopy and, for the first time, by Electron Paramagnetic Resonance spectroscopy using spin-labeled ɛPL. The highest (∼99% for E. coli versus ∼92% for S. aureus) and kinetically the fastest (in 3 h) antibacterial activity with ∼83% for E. coli versus ∼64% for S. aureus bactericidal effect was determined for the wool functionalized by the chemical grafting-to approach. Such an effect may be related to both quantitatively the highest (∼62 gɛPL/kgwool) grafting yield of ɛPL and conformationally its highly flexible “brush-like” structure. Comparably, the enzymatic coupling (∼50 gɛPL/kgwool) giving ∼95% and ∼8% reductions of E. coli and S. aureus, respectively, being additionally reduced to ∼74% and ∼78% by using the grafting-from approach (∼34 gɛPL/kgwool), was identified as the less bactericidally effective (∼63% versus ∼58%). It was also shown that a non-ionic surfactant being used in the durability testing of functionalized wool to washing adheres strongly onto the fibers, thus blocking the amino groups of ɛPL, and, as such, decreases the antibacterial efficiency of the wool, being unaffected in the case when the washing was carried out without surfactant.