## 3 Mechanisms of Action of Antimicrobial Compounds  
The mechanisms by which plant extracts and compounds exert their effects on microbes are varied and complex. These substances can target one or multiple sites, with their effects potentially being additive, synergistic, or antagonistic, thereby influencing bacterial cells through various pathways (Figure 3) [43,111]. I. Alteration in membrane permeability: The plasma membrane is an essential component of bacterial cells, playing a vital role in maintaining cellular integrity, homeostasis, and overall survival. This selectively permeable barrier is primarily composed of a phospholipid bilayer interspersed with proteins that regulate the transport of nutrients, ions,  
Figure 3: Mechanism of action reported for antimicrobial plant extracts. Adapted from [PERSON] et al. [112]. and waste products. Beyond serving as a physical barrier, the membrane houses enzymes essential for energy production, such as those involved in ATP (Adenosine triphosphate) synthesis via the electron transport chain, and facilitates signal transduction and cellular communication. The disruption of the plasma membrane can compromise these essential functions, leading to leakage of intracellular components and ultimately resulting in cell death [113; 114]. Given its important function, the bacterial plasma membrane is a primary target for antimicrobial agents, including those derived from plants. Plant-based antimicrobials, often referred to as phytochemicals, have been utilized for centuries in traditional medicine and have recently gained attention as potential alternatives or supplements to conventional antibiotics. Many of these natural compound's function by altering the permeability of the bacterial membrane, disrupting cellular function, and inducing bacterial cell death [115]. Phenolic compounds, a class of secondary metabolites found in plants, have been shown to damage membrane integrity in a nonspecific manner and inhibit certain electron transport enzymes, thereby exhibiting antimicrobial activity [116]. AMPs represents another promising alternative to traditional antibiotics due to their unique physicochemical properties, effectiveness against a broad spectrum of bacterial species, and distinct mechanisms of action. Typically, AMPs eliminate bacteria by either compromising membrane integrity or penetrating bacterial cells to interact with internal components [117]. For instance, thymol has been shown to affect the permeability of the _Enterobacter sakazkii_ membrane by causing extensive membrane damage, leading to cell death. Thymol treatment results in membrane depolarization, decreased intracellular ATP levels, and alterations in membrane integrity, indicating that it disrupts the membrane's ability to maintain its internal environment [118]. Similarly, eugenol disrupts the cytoplasmic membrane of _E. coli_, increasing membrane permeability and causing leakage of intracellular contents. This disruption is evidenced by morphological changes observed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which reveal damage to the outer membrane and irregular cell shapes. Treatment with eugenol leads to the drainage of cytoplasmic content and a significant release of intracellular ATP, indicating membrane permeabilization. Furthermore, eugenol causes the depolarization of the cytoplasmic membrane, which is crucial for the active uptake of metabolites, ultimately resulting in cell death [119]. Naringenin alters the membrane fluidity and fatty acid profiles of bacterial cells, compromising their structural integrity and function in both Gram-positive and Gram-negative bacteria. In addition to its effects on membrane fatty acids and proteins, this bioflavonoid has also been shown to bind to the DNA of _S. aureus_[120]. Other specific examples are shown in Table 2.