Disrupting cross-adaptation in high-risk MRSA: Sanguinarine as a multi-effective stress sensitizer for environmental and food safety.

Methicillin-resistant Staphylococcus aureus (MRSA) represents a significant public health concern owing to its formidable antibiotic resistance and robust capacity for biofilm formation. The cross-adaptation mechanism enables MRSA to develop tolerance to environmental stressors such as antibiotics, acid, heat and osmotic pressure, leading to the persistence infections and environmental contamination. The cross-adaptation mechanism enables MRSA to develop tolerance to environmental stressors, such as antibiotics, acid, heat and osmotic pressure, leading to the persistence infections and environmental contamination. Here, we identified 261 strains of S. aureus and 9 high-risk MRSA from the environment of dairy farms and raw milk. The natural product Sanguinarine (SAN), derived from feed additives, exhibits effective anti-MRSA and anti-biofilm activity. Notably, SAN enhances the sensitivity of MRSA to antibiotics, acid, heat, and osmotic pressure by disrupting the cross-adaptation mechanism. Mechanistic investigations revealed that SAN significantly reduces the transcriptional level of type I (dnaK, groEL, etc.) and type III (clpB, clpP, etc.) heat stress response genes while markedly upregulating type II (σ) gene. Furthermore, SAN upregulates Na/H antiporters activity, FF-ATPase activity and purine metabolism, while broadly downregulating DNA damage repair genes and disrupting ribosomal function. Additionally, SAN induces non-synonymous mutations in key stress response factors ClpB/L, leading to a loss of conformational homeostasis. SAN elicits a distinct stress response compared to environmental stressors, weakening MRSA's resilience and demonstrating promising capabilities for MRSA clearance and biofilm inhibition. Overall, SAN provides an effective strategy for the clearance of high-risk MRSA and the assurance of public health security.