Unraveling Antibacterial Mechanisms of Surfactants against <i>Staphylococcus aureus</i> via Single-Cell Raman Spectroscopy

Antibacterial agents, particularly surfactants, play crucial roles in the personal and home care industries. However, current methods for assessing their efficacy and mechanism are commonly time-consuming and expensive. Here, we established a ramanome-based approach to investigate the antibacterial mechanisms of cationic and anionic surfactants with varying alkyl chain lengths against <i>Staphylococcus aureus</i> as a model. Our findings further elucidate the synergy between anionic surfactants and acidic pH. Cell membrane integrity was disrupted by all of the surfactants, as revealed by the decrease in Raman bands assigned to major cellular components (nucleic acids, proteins, and cytochrome), leading to the leakage of cellular components. Moreover, the composition of the cell membrane was altered due to insertion of cationic surfactant, evidenced by the emergence of surfactant-characteristic bands in the spectrum of <i>S. aureus</i>; yet this was observed only under acidic conditions for anionic surfactants. Remarkably, changes in Raman bands of staphyloxanthin and S═O which are biomarkers of cellular oxidative states revealed that acidic conditions accelerated cell death induced by the anionic surfactant. These findings illustrate distinct mechanisms of action for cationic and anionic surfactants and suggest that ramanomics offers a rapid, low-cost, comprehensive, and mechanism-revealing approach for the assessment and screening of surfactants.