Toxin - Antitoxin Systems and Virulence Genes in Enterococcus Faecium

Enterococcus is Gram-positive cocci, facultative anaerobic and belong to lactic acid bacteria of the phylum Firmicutes.It is now obvious the virulence of bacteria is associated with virulence genes that are located in special rejoin called pathogenicity islands. TA system is a regulatory system where two set genes encode the toxin and the corresponding antitoxin. TA systems were first described in the mid 80's. The TA system could be harbored by chromosome or plasmid. In all TA systems, antitoxin is unstable and toxin is stable. When the TA system contains on plasmid, the results will be survived daughter cells that inherit the plasmid. The daughter cells that cannot inherit the plasmid harboring TA systems are killed. Because of the degradation of antitoxin, the stable toxin kills the cell. This is called post segregation killing.