Microorganisms and cationic surfactants

Quaternary ammonium salts (QAS) as cationic surfactants with an amphiphilic structure show biocidal activity against non-pathogenic and pathogenic microorganisms (Gram-positive, Gram-negative bacteria, fungi, as well as lipophilic viruses) occurring in planktonic form or forming biofilms. They can also coat the surface of various materials (glass, metal, silicone, polyester) from which medical devices are made, such as: catheters, implants, heart valves, endoprostheses, and this allows inhibiting the adhesion of microorganisms to these surfaces. In their chemical structure, these surfactants contain labile bonds, e.g. ester or amide bonds, which enable the biodegradation of the compounds. Thanks to this, they are classified as “green chemistry”. Their biological activity depends on the length of the hydrophobic chain and the structure of the hydrophilic head of the compound. QAS have an affinity for the cell membrane by interacting with its lipids and proteins, which can lead to its disintegration. They have the ability to inhibit the activity of H+-ATPase of the cell membrane, the enzyme responsible for its electrochemical gradient and the transport of nutrients to the cell, e.g. amino acids. These compounds can influence the lipid composition (quantitative and qualitative) of the cell membrane of microorganisms. They are also inhibitors of respiratory processes and can induce the formation of reactive oxygen species. These surfactants are capable of forming micelles and liposomes in an aqueous environment. They are widely used in medicine (as disinfectants, DNA carriers in gene therapy), in industry and environmental protection (as biocides, preservatives) and in agriculture (as fungicides). The widespread use of QAS in many fields causes the growing resistance of microorganisms to these compounds. A common mechanism that generates reduced susceptibility to QAS is the presence of efflux pumps.