TMT-Based Quantitative Proteomics Revealed the Antibacterial Mechanism of Cinnamaldehyde against MRSA

Natural plant extracts have demonstrated significant potential in alternative antibiotic therapies. Cinnamaldehyde (CA) has garnered considerable attention as a natural antibacterial agent. In this study, Tandem mass tag (TMT) quantitative proteomics combined with Western blot and RT-qPCR methods were employed to explore the antibacterial mechanism of CA against Methicillin-Resistant <i>Staphylococcus aureus</i> (MRSA) at the protein level. The results showed that a total of 254 differentially expressed proteins (DEPs) were identified in the control group and CA treatment group, of which 161 were significantly upregulated and 93 were significantly downregulated. DEPs related to nucleotide synthesis, homeostasis of the internal environment, and protein biosynthesis were significantly upregulated, while DEPs involved in the cell wall, cell membrane, and virulence factors were significantly downregulated. The results of GO and KEGG enrichment analyses demonstrated that CA could exert its antibacterial effects by influencing pyruvate metabolism, the tricarboxylic acid (TCA) cycle, teichoic acid biosynthesis, and the <i>Staphylococcus aureus</i> (<i>S. aureus</i>) infection pathway in MRSA. CA significantly inhibited the expression of recombinant protein MgrA (<i>p</i> < 0.05), significantly reduced the mRNA transcription levels of <i>mgrA</i>, <i>hla</i>, and <i>sdrD</i> genes (<i>p</i> < 0.05), and thermostability migration assays demonstrated that CA can directly interact with MgrA protein, thereby inhibiting its activity. These findings suggest that CA exerts its antibacterial mechanism by regulating the expression of related proteins, providing a theoretical basis for further development of clinical applications of antimicrobial agents derived from natural plant essential oils in the treatment of dairy cow mastitis.