However, the outer membrane of microbial cells forms an effective barrier, which reduces the uptake of hydrophobic substrates.
This disintegration is hypothesised to occur by the formation of pores in the cell membrane of microbial cells thus inducing an increased influx of Ca2+ and H+ into the cells (Thrane et al. 1999).
The hydroxyl radicals and radical anions are the primary oxidizing species in the photocatalytic oxidation processes, which result in the removal of organic compounds (e.g., dyes, pesticides, phenols and other organic pollutants) and induce oxidative stress to the cell membrane of microbial organism [11, 12, 13].
The toxic effect of ENPs on microorganisms is size, type, and concentration-dependent, and exerted by varying mechanisms such as the formation of reactive oxygen species and free radicals that result in lipid peroxidation of cell membrane, disruption of microbial physiology, and metabolic processes.
Outer membrane proteins of microbial pathogens serve essential roles in engaging the host environment and can be important immunotherapeutic targets [ 49].
In the search for new antibiotics, cationic antimicrobial peptides (CAMPs) offer a viable alternative to conventional antibiotics, as they physically disrupt the bacterial membranes, leading to lysis of microbial membranes and eventually cell death.
Antimicrobial peptides are released at epithelial surfaces and disrupt the membranes of many microbial pathogens.
In other studies, anti-microbial activity of graphene oxide (GO) has been attributed to induction of microbial membrane damage, disturbance of the membrane potential [93] and electron transport [94], as well as oxidative stress by increased production of reactive oxygen species (ROS) [95, 96].
The increased uptake of propidium iodide in the hydroxychavicol treated cells of C. albicans in our study, further confirmed the earlier findings that hydroxychavicol alters the cell membrane structure, resulting in the disruption of the permeability barrier of microbial membrane structures [ 30].
Essential oils on the other hand which are typically a mixture of terpenes and/or terpenoids are postulated to exhibit anti-bacterial activity by disrupting the permeability barrier of microbial membrane structures [[ 31]], with some studies even showing the membrane disrupting activities of some plants essential oils against both Gram negative and Gram positive bacteria [[ 24],[ 31]].
This characteristic conformation of the peptides, in the course of microbial membrane invasion, allows the non-polar face of their α-helical structure to interact with the membrane lipid core while at the same time permitting its hydrophilic face to engage in electrostatic interactions with the membrane lipid headgroup region (Phoenix et al. 2002).
