Prokaryotes and eukaryotes have coexisted for many years, during which time they have been exposed to the signals produced and released by the other. The organisms of two kingdoms have also learnt to sense their various molecules including QS signals to influence gene expression and behavior in a process called inter- kingdom signaling

For cell- to-cell communication, these bacteria employ the quorum sensing (QS) system to pass on information of the density of the bacterial population and collectively switch on virulence factor production, biofilm formation, and resistance development. Thus, QS allows bacteria to behave as a community to perform tasks which would be impossible for individual cells, e.g., to overcome defense and immune systems and establish infections in higher organisms.

Quorum-sensing (QS) system is a rapidly developing field in which we are gradually expanding our understanding about how bacteria communicate with each other and regulate their activities in bacterial sociality.

researchers focused on eliminating bacteria using conventional antimicrobials. In the 1950s, success in rescuing Clostridium difficile infection using fecal microbiota transplantation (FMT) introduced a new perspective, i.e., introduction of a mixed microbial community, instead of eliminating specific bacteria, may benefit the host in fighting microbial infection. Around the same time, a phenomenon of intercellular communication in specific bacterial communities was discovered