Moreover, there is no evidence as of now that the distribution of AHL synthase and the species are correlated. Contrary to LuxI genes, the receptors of AHLs, LuxR protein and their genes, are highly variable among species. Signalling Mechanism Bacterial quorum signalling begins with the N-AHLs secreted into the environment. In the process of quorum sensing, first the LuxI protein synthesizes an acylated homoserin-lactone molecule which can pass through cell membrane along the gradient through diffusion to the environmental space. When the concentration of these autoinducers in the environment is lower than inside the cell, they will move down the gradient and will leave the cell, therefore, they will not attach to their receptor, LuxR, which is in the cytoplasm. When the population of bacteria reaches a threshold, and the concentration of the autoinducers in the environment is higher than inside the cell, they will move along the gradient into the cell and will attach to the receptor. Thus, the LuxR-AHL complex will be formed. This complex will bind to a 20 base pair (bp) section of DNA, called the lux box. This region is in or near the lux promoter region, which is located ~40 bp upstream of the regulated gene. Because LuxR is bound to the promoter, RNA polymerase is recruited to this promoter region and the gene expression is induced. Moreover, the LuxR-AHL complex will upregulate the transcription of LuxI protein which will increase the production of AHLs (positive feedback loop). The transcription of the target genes will be regulated, and as gene expression of an entire population will be coordinated. Several studies have been investigating on the potential AHLs effective in infection and resistance to antibiotics. The LuxR–LuxI system mediated by AHLs is the best screened QS system in multi-drug resistant bacteria species. Quorum Quenching As opposed to quorum sensing, quorum quenching, prevents bacterial communication and influences their gene expression. Targets of the quorum quenching are the signal molecules, the biosynthetic machinery of signal molecules, and the regulatory proteins that perceive these signal molecules with the AHL degradation via AHL degrading enzymes and limiting signal accumulation being the main mechanism. The AHLs are degraded by enzymes through three mechanisms: lactone hydrolysis, amide bond hydrolysis, and acyl chain modification. Lactone hydrolysis occurs when AHL Lactonase hydrolyzes homoserine lactone rings. This process was first observe din Bacillus species. AHL acylases catalyze the complete and irreversible destruction of AHLs