Antimultidrug-resistant bacterial activity of microwave solvolysis lignin from woody biomass

Drug-resistant bacteria are a serious concern for human health. Thus, protective substances need to be urgently developed to inhibit the propagation of such bacteria in living environments. We herein report about antibacterial activity of lignin, which was developed via chemical alteration of native lignin in wood. Japanese cedar (Cryptomeria japonica) wood was degraded via microwave solvolysis in an equivolume mixture of 2 % (w/w) aqueous sulfuric acid, ethylene glycol, and toluene at 190 °C for 60 min and fractionated via extraction with toluene, ethyl acetate, and ethanol. The ethyl acetate extract (jEAE) exhibited ≥ 98.5 % inhibitory activity against the drug- and multidrug-resistant strains of Streptococcus pneumoniae. jEAE also exhibited strong inhibitory activity against two nondrug-resistant S. pneumoniae and one Streptococcus pyogenes strains. Lignin-derived monomers having guaiacyl nuclei were detected as major fragments using pyrolysis gas chromatography–mass spectrometry (GC–MS), indicating that jEAE is a solvolysis lignin. In 1H–13C-edited heteronuclear single quantum coherence nuclear magnetic resonance (NMR), signals of guaiacyl nuclei were observed, but those from side chains of β-O-4, β-5, and 5–5/4-O-β substructures disappeared. 31P NMR revealed that jEAE possesses lower and higher amounts of aliphatic and phenolic OH groups, respectively, than milled wood lignin. The high antidrug-resistant bacterial activity of the structure-altered lignin provides a new approach for suppressing the growth of drug-resistant bacteria using lignocellulosic biomass.