**2. Quorum sensing in** *Staphylococcus aureus*

Quorum sensing is a well-known phenomenon used mainly by prokaryotes for communication among themselves [14]. Particularly in bacteria quorum sensing is monitored by a set of signaling molecules called autoinducers as density dependent variables. They are released by bacteria around their surrounding environment which up on reaching at particular concentration develop a well-coordinated response. Density of autoinducers is monitored by bacteria for tracking changes in cell number and to alter the gene expression pattern. This is also a factor that is responsible for resistance of bacteria against antibiotics [15, 16]. Quorum sensing in *Staphylococcus aureus* has been coordinated through modified oligopeptide

**Figure 1.** *Mechanistic insight of quorum sensing in* Staphylococcus aureus.

*Mechanistic Insights of Drug Resistance in* Staphylococcus aureus *with Special Reference... DOI: http://dx.doi.org/10.5772/intechopen.100045*

known as autoinducing peptide (AID). In the pathophysiology of *Staphylococcus aureus* regarding quorum sensing, biphasic mechanism exist. At lower cell density, *Staphylococcus aureus* generally express protein factors i.e. Coagulase and fibronectin binding proteins A and B etc. which promote their attachment as well as colonization while at higher cellular density *Staphylococcus aureus* repress these traits and initiate secretion of toxins and proteases that needed for dissemination. The switching of this gene expression is controlled by Agr quorum sensing system that consist of autoinducing peptide (AID) encoded by agrD and two other sensor kinase-response regulators called AgrC and AgrA (**Figure 1**) [17–19].
