DL-propargylglycine reverses beta-lactam resistance in Streptococcus agalactiae.

Streptococcus agalactiae (GBS) is a major pathogen causing severe infections in human and economic loss in animal farming, where β-lactams remain first-line therapy. However, emerging β-lactam resistance, including WHO-priority penicillin-resistant strains, threatens clinical efficacy, creating an urgent need for resistance-breaking adjuvants. In this study, we demonstrate that DL-Propargylglycine (PAG), an inhibitor of cystathionine-γ-lyase inhibitor, exclusively synergizes with β-lactams to reverse resistance in ampicillin-resistant GBS (AR-GBS) and other streptococci, overcoming tolerance in persisters and biofilms. Mechanistically, PAG potentiates antibiotic lethality through dual pathways: metabolic activation via enhanced central carbon metabolism for ROS production and cell envelope remodeling via concurrent downregulation of peptidoglycan biosynthesis genes and upregulation of capsular polysaccharide synthesis. This disrupts cell wall architecture, increases membrane permeability and accelerates antibiotic influx. While in vivo therapeutic efficacy in zebrafish was limited, PAG represents an adjuvant that overcomes β-lactam resistance through metabolic and membrane remodeling, paving the way for optimized derivatives.