FIGURE 1.

(A) Chemical structural formula of CHX digluconate. (B) Scanning electron microscopic (SEM) visualization of an in vitro polymicrobial biofilm comprising Actinomyces naeslundii, Actinomyces odontolyticus, and S. mutans (methodology as described in Cieplik et al., 2018b,c) following treatment with CHX (0.2%; 10 min). Vesicle-like structures on the surfaces of bacterial cells indicate membrane damage (indicated by red arrows). SEM images are reprinted from Cieplik et al. (2018b). (C–F) Scheme depicting the mode of action of CHX toward bacterial cytoplasmic membranes. The bacterial cytoplasmic membrane carries a net negative charge and is composed of a phospholipid bilayer with embedded proteins. The phospholipid bilayer is stabilized by divalent cations such as Ca²⁺ and forms a hydrophobic environment, which is essential to moderate the functionality of the embedded proteins (C). CHX (as a cationic agent) binds to the negatively charged bacterial cell surface and initially interacts with the cytoplasmic membrane. Thereby, CHX bridges between pairs of phospholipid headgroups and displaces the associated divalent cations (D). Progressive decrease in fluidity of the outer phospholipid layer with creation of hydrophilic domains within the bilayer affecting the osmoregulation and metabolic activity of the cytoplasmic membrane and its associated enzymes (E,F). This scheme was adopted and modified from Gilbert and Moore (2005).