Multi-target anti-MRSA mechanism and antibiotic synergistic effect of marine alkaloid Ascomylactam A in vitro and in vivo against clinical MRSA strains

Methicillin-resistant Staphylococcus aureus (MRSA), as a kind of multi-drug resistant bacteria, often causes serious sanitary infection problems. Marine fungi are seen as a promising source of lead compounds for antibiotics. In this research, the antibacterial activity, antibiotic synergistic effect and mechanism of the alkaloid Ascomylactam A (AsA) derived from the marine fungus Microascus sp. SCSIO 41821 were investigated in vivo and in vitro. Antibacterial assays showed that AsA had excellent antibacterial activity and inhibition of biofilm formation against MRSA SC41993, and exhibitted synergistic antibacterial effects with clinical antibiotics. Transcriptomics revealed the potential mechanism that AsA affected the formation of MRSA biofilm, cell wall synthesis and virulence through LytSR, VraSR, ArgAC and KdpDE two-component system (TCS). In addition, by treatment with AsA, it was found that AdhE protein was a potential target for oxidative stress and lipid peroxidation in MRSA, and the resistance of MRSA was reversed by regulating some genes. In vivo experiments showed that AsA combined with gentamicin sulfate (GMS) had a better therapeutic effect than alone against clinical MRSA USA300, especially in the heart. In this study, the antibacterial mechanism of decahydrofluorene-class alkaloids was preliminarily investigated, supporting the potence of AsA as a promising therapeutic agent to combat MASA infections.