Antibacterial Properties of Heteronium Lignin Containing Materials Against ESKAPE Pathogens

The rise of antibiotic resistance and a declining antimicrobial pipeline pose significant threats to public health. The ESKAPE pathogens—Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.—are critical multidrug-resistant bacteria urgently needing effective therapies. Lignin has shown promise as a renewable antibacterial material, and its chemical modifications can enhance its antimicrobial activity. In this study, quaternary ammonium (QALs) and quaternary phosphonium (QPLs) lignin materials were derived from softwood (pine) through chloromethylation and further functionalized with tertiary amines and phosphines. Successful synthesis was confirmed via NMR, FT-IR, and elemental analysis. The antibacterial effectiveness of QALs and QPLs against ESKAPE pathogens was evaluated through growth inhibition zone (ZOI) assays and minimum bactericidal concentrations (MBCs). QPLs exhibited greater antibacterial activity than QALs, with QPLs containing a trihexyl carbon chain (C6) demonstrating superior effectiveness compared to those with trioctyl carbon chain (C8). The ZOI test also confirmed that QPLs reached optimal antibacterial activity at C6. The film composed from cellulose acetate (CA) and QPLs containing C6 was obtained by electrospinning in a dimethylacetamide/acetone mixture. The electrospun film of CA-QPL was characterized morphologically using scanning electron microscopy and assessed for its biofilm inhibitory properties against Gram-positive and Gram-negative bacteria. QPL demonstrates dose-dependent cytotoxicity at elevated concentrations; however, it maintains a commendable safety margin relative to its antibacterial efficacy.