Salt Elicitation of Centella asiatica Enhances Antimicrobial and Keratinocyte Wound-Closure Activity: From Germplasm Screening to Nicotinamide Accumulation

Centella asiatica (L.) Urb. is valued for skin repair. Salt (NaCl) treatment is an inexpensive way to alter its metabolome, but its effect on bioactivity across germplasm is unknown. Thirty-nine Thai accessions were grown with or without 100 mM NaCl for 10 days, and leaf extracts were screened against Escherichia coli, Staphylococcus aureus, and Candida albicans using a growth ratio (GR), growth with the NaCl extract relative to the untreated one. The most responsive accession, PHE, was profiled by untargeted LC-HRMS and tested in kinetic growth, HaCaT viability, and scratch-wound closure assays. NaCl extracts reduced bacterial growth to 0.88 (E. coli) and 0.90 (S. aureus) of the untreated level, but responses were genotype-dependent. In PHE, nicotinamide was the most strongly induced metabolite (9.3-fold by LC-HRMS, 9.6-fold by HPLC). The NaCl extract inhibited E. coli by 87% (untreated extract 33%), was non-cytotoxic, increased keratinocyte metabolic activity, and raised scratch-wound closure to 84% of the positive control. Pure nicotinamide reproduced this closure (83%), but only at a concentration far above its content in the extract. Salt elicitation therefore enhances antimicrobial and wound-closure activity in responsive genotypes, with nicotinamide as a marker of the response and a plausible but not sole contributor.