Listeriolysin O (LLO)

Listeriolysin O (LLO) is a hemolysin produced by the bacterium Listeria monocytogenes, the pathogen responsible for causing listeriosis. The toxin may be considered a virulence factor, since it is crucial for the virulence of L. monocytogenes. Listeriolysin O is encoded by the gene hly, which is part of a pathogenicity island called LIPI-1. Transcription of hly, as well as other virulence factors of L. monocytogenes within LIPI-1, is activated by the protein encoded by prfA gene. prfA is thermoregulated by the PrfA thermoregulator UTR element, such that translation of prfA maximally occurs at 37°C and is nearly silent at 30°C. Since 37°C is within the range of normal body temperature, PrfA protein, as well as listeriolysin O and other virulence factors regulated by PrfA, is only produced when L. monocytogenes is in a host.