cytolysins

Cytolysins are a broad class of toxins that cause lysis of host cells by damaging the plasma membrane. They are produced by a range of organisms, including bacteria, fungi, plants, and animals, and they often function as virulence factors that promote tissue damage and disseminate infection. Cytolysins can act on many cell types, including red and white blood cells, epithelial and endothelial cells, contributing to inflammation, necrosis, and systemic disease.

Most cytolysins disrupt membranes through two main mechanisms. The first involves pore formation, where toxin molecules bind to the membrane, oligomerize, and insert to create transmembrane pores that collapse ion gradients and drive cell death. The second involves enzymatic degradation of membrane lipids, such as phospholipases that hydrolyze phospholipids to disrupt the bilayer. A common theme is reliance on membrane components such as cholesterol for binding or activity, though different toxins have distinct molecular requirements and pore sizes.

Representative examples include cholesterol-dependent cytolysins, produced by several Gram-positive bacteria. Streptolysin O and streptolysin S from Streptococcus pyogenes are well-known hemolysins; listeriolysin O from Listeria monocytogenes is a pore-forming CDC; perfringolysin O and alpha-toxin from Clostridium perfringens include lecithinase activity that degrades phospholipids. Pneumolysin from Streptococcus pneumoniae is another notable cytolysin.

Clinically, cytolysins contribute to tissue damage during infections and can be detected by characteristic hemolysis patterns, cytotoxicity assays, or neutralization studies. Their study informs understanding of pathogenesis and the development of therapeutic or preventive strategies.