The pathogenicity of Staphylococcus aureus is profoundly affected by the quorum sensing mechanism which is regulated by the accessory gene regulator (agr) system. This system composed of 4 groups of genes which govern more than 70 genes, including 23 that are recognized as virulence factors genes. These genes enhancing the synthesis of extracellular toxins such as (haemolysins, proteases, enterotoxins, etc.) and decrease the production of cell surface-correlated proteins (microbial surface substances realising adhesive matrix molecules related to biofilm formation). So up-regulation of agr genes promotes dispersion while down-regulation results in excessive biofilm thickness and lack of structure. This increases the virulence of bacteria.

The control of virulence factors by agr is crucial for the development of illness. Each section of the genome plays a role in a variety of traits within the population of bacteria, increasing the chances of survival in various settings. Agr serves as a fundamental quorum sensing mechanism, enabling bacteria to modulate gene expression based on the density of the population.