Negletein as a multifaceted therapeutic approach in overcoming MRSA-induced pneumonia and septic arthritis amidst antimicrobial resistance.

Abstract

Antimicrobial resistance in Staphylococcus aureus, especially methicillin resistant strains, contributes to severe pneumonia and septic arthritis and undermines the efficacy of standard antibiotics. We explore an antivirulence approach that targets MgrA, a global transcriptional regulator of pathogenic programs and resistance traits, and identify negletein as a small molecule that engages this target. At efficacious exposures negletein is nonbactericidal, separating virulence control from growth and with the potential to reduce selection pressure compared with bactericidal strategies. Thermal shift and intrinsic fluorescence quenching assays support direct binding to MgrA and are consistent with the involvement of residues important for the interaction. In line with target engagement, negletein reduces MgrA dependent transcription, dampens Agr quorum sensing output, and alters the surface proteome. These changes are associated with reduced adhesion to host substrates and epithelial invasion and with increased neutrophil chemotaxis. Across in vitro and in vivo models, negletein reduced cytotoxicity and intracellular bacterial burden. In murine MRSA pneumonia, treatment was associated with improved survival, lower pulmonary bacterial loads, and reduced inflammatory readouts. In experimental septic arthritis, treatment reduced joint pathology and tissue bacterial burden. Taken together, the data support MgrA as a viable antivirulence target, nominate negletein as a starting point for MRSA antivirulence development, and suggest a resistance sparing strategy that focuses on disarming pathogenicity rather than suppressing viability.