Exploring in vitro efficacy of rCHAPk with antibiotic combinations, and promising findings of its therapeutic potential for clinical-originated MRSA wound infection

The increasing threat of antimicrobial-resistant bacteria, particularly Staphylococcus aureus, which rapidly develops multidrug resistance and commonly colonizes wound surfaces, demands innovative strategies. Phageencoded endolysins offer a dual-purpose approach as topical therapies for infectious skin wounds and synergistic agents to reduce high-dose antibiotic dependence. This study explores recombinant CHAPk (rCHAPk), efficiently synthesized within 3 h, displaying broad-spectrum antibacterial activity against 10 Gram-positive strains, including resistant variants, with rapid bactericidal kinetics. Application of 10 mu g of rCHAPk reduced OD600 by 0.4 within 5 min against a clinical methicillin-resistant S. aureus (MRSA) strain. Combining rCHAPk (1.875 mu g/mL) with oxacillin/vancomycin lowered their minimum bactericidal concentrations to 1 mu g/mL from initial values over 64 mu g/mL and 32 mu g/mL, respectively, with a fractional inhibitory concentration index below 0.1. rCHAPk retained efficacy after one year of refrigerated storage. In in vivo experiments, rCHAPk outperformed commercial fucidin therapy in MRSA-induced murine wound models over two weeks, enhancing wound healing by modulating pro-inflammatory cytokine responses and the proliferative phase. This study, for the first time, investigates rCHAPk's in vitro combination with antibiotics and wound healing parameters, highlighting its potential as a potent antibacterial agent synergizing with antibiotics to address antibioticresistant bacterial wound infections.