Nowadays, there are known twenty transcription factors (TF's) involved in QS; all of them having multiple interactions with each other . Las, Rhl, PQS, and IQS are related to the activation of QS and the production of multiple virulence factors (elastase, protease, rhamnolipids, pyocyanin, hydrogen cyanide) ; Las and Rhl are systems of the Lux type, while PQS is a quinolone dependent system.